Thallus with _Scytonema_ gonidia.
Spores elongate, 3-septate 1. Petractis Fr.
Thallus with _Trentepholia_ gonidia.
Asci 6-8-spored.
Spores simple 2. Jonaspis Th. Fr.
Spores 1-septate 3. *Microphiale A. Zahlbr.
Spores septate or muriform 4. Gyalecta Ach.
Asci 12-many-spored.
Spores 1-septate 5. *Ramonia Stizenb.
Spores fusiform or acicular,
many-septate 6. Pachyphiale Lönnr.
Apothecia carbonaceous.
Spores elongate, 2-3-septate 7. *Sagiolechia Massal.
XXX. _COENOGONIACEAE_
There are only two genera in this small family, _Coenogonium_ with
_Trentepohlia_ gonidia, and _Racodium_ with _Cladophora_. Both genera
follow the algal form and are filamentous. In _Coenogonium_ the filaments
are sometimes matted into a loose felted expansion. The genus is mainly
tropical or subtropical and mostly rather light-coloured. There is only
one British species, _C. ebeneum_[1050], a sterile form, in which the
hyphae are very dark-brown; it often covers large areas of stone or rock
with its sooty-like creeping filaments.
_Racodium_ includes 2 (?) species. One of these, _R. rupestre_, is
sterile and resembles _C. ebeneum_ in form and colour.
The apothecia of _Coenogonium_ are waxy and light-coloured; they are
borne laterally on the filaments; the spores are simple or 1-septate.
Thallus with _Trentepohlia_ gonidia 1. Coenogonium Ehrenb.
Thallus with _Cladophora_ gonidia 2. Racodium Fr.
XXXI. _LECIDEACEAE_
One of the largest lichen families as regards both genera and species,
and of world-wide distribution. The algal cells are Protococcaceae. The
thallus is mostly crustaceous but it becomes squamulose in _Psora_, a
section of _Lecidea_; and in _Sphaerophoropsis_, a Brazilian genus, there
are small upright fronds or stalks with lateral apothecia. The prevailing
colour of the thallus is some shade of grey, but it ranges from white or
yellow to dark-brown or almost black. Cephalodia appear in some of the
species.
The apothecia have a proper margin only, no gonidia taking part in the
fruit-formation. They may be soft and waxy (biatorine) or hard and
carbonaceous (lecideine). The genera are mainly based on spore characters
which are very varied.
The arrangement of genera given below follows that of Zahlbruckner;
in several instances, both as to the limitations of genera and to the
nomenclature, it differs from that of British text-books, though the
general principle of classification is the same.
Thallus crustaceous non-corticate.
Spores simple.
Spores small, thin-walled.
Spores colourless 1. Lecidea Ach.
Spores brown 2. *Orphniospora Koerb.
Spores large, thick-walled 3. Mycoblastus Norm.
Spores 1-septate.
Spores small, thin-walled 4. Catillaria Th. Fr.
Spores large, thick-walled 5. Megalospora Mey. and Flot.
Spores elongate, 3-multi-septate.
Spores elongate, narrow, thin-walled 6. Bacidia A. Zahlbr.
Spores elongate, large and
thick-walled 7. Bombyliospora De Not.
Spores muriform.
Spores colourless; on trees 8. Lopadium Koerb.
Spores colourless to brown; on rocks 9. Rhizocarpon Th. Kr.
Thallus warted or squamulose, corticate.
Spores elongate, 1-7-septate,
thin-walled 10. Toninia Th. Fr.
Thallus of upright podetia-like small fronds.
Spores ellipsoid, becoming 1-septate 11. *Sphaerophoropsis Wain.
XXXII. _PHYLLOPSORACEAE_
A small family of exotic lichens with a somewhat more developed thallus
than that of the Lecideaceae, being in both of the genera squamulose or
almost foliose.
The apothecia are without a thalline margin; they are biatorine or
lecideine; the hypothecium is formed of plectenchyma and is purple-red
in one species, _Phyllopsora furfuracca_. The two genera differ only
in spore characters. There are fifteen species, mostly corticolous,
belonging to _Phyllopsora_; only one, from New Zealand, is recorded for
_Psorella_.
Spores simple 1. *Phyllopsora Müll.-Arg.
Spores elongate, septate 2. *Psorella Müll.-Arg.
XXXIII. _CLADONIACEAE_
Associated with Lecideaceae in the type of apothecium, but differing
widely in thallus formation. The latter is of a twofold type: the
primary thallus is crustaceous, squamulose, or very rarely foliose; the
secondary thallus or podetium, upright, simple or branched, is terminated
by the apothecia, or broadens upwards to cup-like scyphi. Algal cells,
Protococcaceae, according to Chodat, _Cystococcus_.
Much attention has been given to the origin and development of the
podetia in this family. They are superficial on granule or squamule
except in the monotypic Himalayan genus _Gymnoderma_ where they are
marginal on the large leaf-like lobes. Though in origin the podetia are
doubtless fruit stalks, they have become in most cases vegetative in
function.
The fruits are coloured yellowish, brown or red (or dark and carbonaceous
in _Pilophorus_), and are borne on the tips of the branches or on the
margins of the scyphi. In _Glossodium_ and _Thysanothecium_—the former
from New Granada, the latter from Australia—the apothecia occupy one side
of the widened surface at the tips.
Cephalodia are developed on the primary thallus of _Pilophorus_, and on
the podetia of _Stereocaulon_ and _Argopsis_.
Podetia simple, short, not widening upwards.
Podetial stalks naked.
Primary thallus thin, continuous 1. Gomphillus Nyl.
Primary thallus granular or
squamulose 2. Baeomyces Pers.
Primary thallus foliose.
Podetia superficial 3. *Heteromyces Müll.-Arg.
Podetia marginal 4. *Gymnoderma[1051] Nyl.
Podetial stalks granular, squamulose 5. Pilophorus Th. Fr.
Podetia short, widening upwards.
Podetia simple above, rarely
divided 6. *Glossodium Nyl.
Podetia lobed, leaf-like 7. *Thysanothecium Berk. &
Mont.
Podetia elongate, variously branched, or
scyphous and hollow 8. Cladonia Hill.
Podetia elongate, not scyphous, the stalks solid.
Spores elongate, septate 9. Stereocaulon Schreb.
Spores muriform 10. *Argopsis Th. Fr.
XXXIV. _GYROPHORACEAE_
A small family of foliose lichens allied to Lecideaceae by the character
of the fruit—a superficial apothecium in the formation of which the
gonidia take no share. There are only three genera, distinguished
by differences in spore and other characters. _Dermatiscum_ has
light-coloured thallus and fruits; of the two species, one occurs in
Central Europe, the other in North America. _Umbilicaria_ and _Gyrophora_
are British; they are dark-coloured rock-lichens and are extremely
abundant in Northern regions where they are known as “tripe de roche.”
Algal cells Protococcaceae.
_Umbilicaria_, _Dermatiscum_, and some species of _Gyrophora_ are
attached to the substratum by a central point. Other species of
_Gyrophora_ are rhizinose. In all there is a cortex of plectenchyma
above and below. In _Gyrophora_ the thallus may be monophyllous as in
_Umbilicaria_, or polyphyllous and with or without rhizinae. New lobes
frequently arise from protuberances or warts on the older parts of the
thallus. At the periphery, in most species, growth is equal along the
margins, in _G. erosa_[1052] the edge is formed of numerous anastomosing
lobes with lateral branching, the whole forming a broadly meshed open
network. Further back the tissues become continuous owing to the active
growth of the lower tissue or hypothallus, which grows out from all
sides and meets across the opening. The overlying layers, with gonidia,
follow more slowly, but they also in time become continuous, so that the
“erose” character persists only near the periphery. This forward growth
of the lower thallus occurs in other species, though to a much less
marked degree.
There is abundant detritus formation in this family; the outer layers of
the cortex are continually being sloughed, the dead tissues lying on the
upper surface as a dark gelatinous layer, continuous or in small patches.
On the under surface the cast-off cortex gathers into a loose confused
mass of dead tissues.
Asci 8-spored.
Spores mostly simple (disc gyrose) 1. Gyrophora Ach.
Spores 1-septate 2. *Dermatiscum Nyl.
Asci 1-2-spored.
Spores muriform 3. Umbilicaria Hoffm.
XXXV. _ACAROSPORACEAE_
Thallus foliose, squamulose or crustaceous, sometimes scarcely developed.
Algal cells Protococcaceae.
Into this family Zahlbruckner has gathered the genera in which the asci
are many-spored, as he considers that a character of great importance in
determining relationship, but he has in doing so overlooked other very
great differences. The fruit-bodies are round and completely enclosed
in a thalline wall in _Thelocarpon_, which has however no perithecial
wall. They have a proper margin only (lecideine) in _Biatorella_, and a
thalline margin (lecanorine) in the remaining genera. In _Acarospora_ the
apothecia are sunk in the thallus. Stirton’s genus _Cryptothecia_[1053]
is allied to _Thelocarpon_ in the fruit-formation, but the basal thallus
is well developed and the spores are few in number and variously divided.
Thallus none.
Apothecia (or perithecia) in thalline
warts 1. Thelocarpon Nyl.
Thallus crustaceous.
Apothecia lecideine; spores simple 2. Biatorella Th. Fr.
Apothecia lecanorine; spores septate 3. *Maronea Massal.
Thallus of small squamules 4. Acarospora Massal.
Thallus almost foliose, attached
centrally 5. *Glypholecia Nyl.
XXXVI. _EPHEBACEAE_
A family of very simple structure either filamentous, foliose or
crustaceous. The algal cells which give a dark colour to the thallus
are _Stigonema_ or _Scytonema_, members of the blue-green Myxophyceae,
and consist of minute simple or branched filaments—single cell-rows in
_Scytonema_, compound in _Stigonema_.
In some of the genera the lichen hyphae travel within the gelatinous
sheath of the filaments, both algae and hyphae increasing by apical
growth so that filaments many times the length of the alga are formed as
in _Ephebe_. In others the filaments scarcely increase beyond the normal
size of the alga as in _Thermutis (Gonionema)_; or the gelatinous algal
cells may be distributed in a stratum of hyphae.
The apothecia are minute and almost closed; they may be embedded in
swellings of the thallus, or are more or less superficial. The spores are
rather small, colourless and simple or 1-septate.
The lichens of this family are rock-dwellers and are mostly to be found
in hilly or Alpine regions. A tropical species, _Leptogidium dendriscum_,
occurs in sterile condition in south-west Ireland. There are few species
in any of the genera.
Algal cells _Scytonema_.
Thallus minutely fruticose,
non-corticate 1. Thermutis Fr.
Thallus minute, of felted filaments,
cortex one cell thick 2. *Leptodendriscum Wain.
Thallus of elongate filaments, cortex
of several cells 3. Leptogidium Nyl.
Thallus foliose or fruticose, cellular
throughout 4. Polychidium Ach.
Thallus crustaceous, non-corticate 5. Porocyphus Koerb.
Algal cells _Stigonema_.
Thallus minutely fruticose,
non-corticate 6. Spilonema Born.
Thallus of long branching filaments.
Spores septate; paraphyses wanting 7. Ephebe Fr.
Spores simple; paraphyses present 8. Ephebeia Nyl.
Thallus crustaceous; upper surface
non-corticate, lower surface
corticate 9. *Pterygiopsis Wain.
XXXVII. _PYRENOPSIDACEAE_
In this family are included gelatinous lichens of which the gonidium
is a blue-green alga with a thick gelatinous coat, either _Gloeocapsa_
(including _Xanthocapsa_) or _Chroococcus_. In _Gloeocapsa_ and
_Chroococcus_ the gelatinous envelope is often red, in _Xanthocapsa_
it is yellow, and these colours persist more or less in the lichens,
especially in the outer layers.
The thallus is in many cases a formless gelatinous crust of hyphal
filaments mingling with colonies of algal cells as in _Pyrenopsis_;
but small fruticose tufts are characteristic of _Synalissa_, and
larger foliose and fruticose thalli appear in some exotic genera. A
plectenchymatous cortex is formed on the thallus of _Forssellia_, a
crustaceous genus from Central Europe, with two species only; the whole
thallus is built up of a kind of plectenchyma in some others, but in most
of the genera there is no tissue formed.
The apothecia, as in Ephebaceae, are generally half-closed.
Thallus with _Gloeocapsa_ gonidia.
Thallus crustaceous.
Spores simple 1. Pyrenopsis Nyl.
Spores 1-septate 2. *Cryptothele Forss.
Thallus shortly fruticose 3. Synalissa Fr.
Thallus lobate, centrally attached 4. *Phylliscidium Forss.
Thallus with _Chroococcus_ gonidia.
Thallus crustaceous 5. Pyrenopsidium Forss.
Thallus lobate, centrally attached 6. *Phylliscum Nyl.
Thallus with _Xanthocapsa_ gonidia.
Thallus crustaceous.
Thallus non-corticate.
Spores simple.
Apothecia open, asci 8-spored 7. Psorotichia Forss.
Apothecia covered, asci
many-spored 8. *Gonohymenia Stein.
Spores 1-septate.
Apothecia closed 9. *Collemopsidium Nyl.
Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr.
Thallus lobate, centrally attached.
Spores simple.
Thallus plectenchymatous
throughout 11. *Anema Nyl.
Thalline tissue of loose hyphae 12. *Thyrea Massal.
Cortex of upright parallel hyphae 13. *Jenmania Wächt.
Spores 1-septate.
Thalline tissue of loose hyphae 14. *Paulia Fée.
Thallus fruticose.
Thallus without a cortex 15. *Peccania Forss.
Thallus with cortex of parallel
hyphae 16. *Phloeopeccania Stein.
XXXVIII. _LICHINACEAE_
The only family of lichens associated with _Rivularia_ gonidia, the
trichomes of which retain their filamentous form to some extent in the
more highly developed genera; they lie parallel to the long axis of the
squamule or of the frond except in _Lichinella_ in which genus they are
vertical to the surface. The thallus may be crustaceous, or minutely
foliose, or fruticose; in all cases it is dark-brown in colour, and the
gelatinous character is evident in the moist condition. The best known
British genus is _Lichina_ which grows on rocks by the sea.
The apothecia are more or less immersed in the tissue; in _Pterygium_
and _Steinera_ they are open and superficial (the latter monotypic
genus confined to Kerguelen). They are also open in _Lichinella_ and
_Homopsella_, both very rare genera. The spores are colourless and
simple except in _Pterygium_ and _Steinera_ where they are elongate, and
1-3-septate.
Thallus crustaceous squamulose.
Apothecia immersed in thalline warts 1. *Calothricopsis Wain.
Apothecia superficial, with thalline
margin 2. *Steinera A. Zahlbr.
Apothecia superficial, without a
thalline margin 3. Pterygium Nyl.
Thallus of small fruticose fronds.
Gonidia occupying the central strand 4. *Lichinodium Nyl.
Gonidia not in the centre.
Apothecia immersed 5. Lichina Ag.
Apothecia superficial.
Paraphyses present 6. *Lichinella Nyl.
Paraphyses absent 7. *Homopsella Nyl.
XXXIX. _COLLEMACEAE_
The most important family of the gelatinous lichens and the most
numerous. _Collema_ is historically interesting as having first suggested
the composite thallus. Algal cells, _Nostoc_, which retain the chain-like
form except in _Leprocollema_, a doubtful member of the family. The
thallus varies from indeterminate crusts to lobes of considerable size;
occasionally the lobes are narrow and erect, forming minute fruticose
structures. In the more primitive genera the thallus is non-corticate,
but in the more evolved, the apical cells of the hyphae coalesce to form
a continuous cellular cortex, one or more cells thick, well marked in
some species, in others rudimentary; the formation of plectenchyma also
occurs occasionally in the apothecial tissues of some non-corticate
species.
The apothecia are superficial except in _Pyrenocollema_, a monotypic
genus of unknown locality. They are generally lecanorine, with gonidia
entering into the formation of the apothecium: in some genera they are
lecideine or biatorine, being formed of hyphae alone. The spores are
colourless and vary in form, size and septation.
Apothecia immersed; spores fusiform,
1-septate 1. *Pyrenocollema Reinke.
Apothecia superficial.
Thallus without a cortex.
Spores simple, globose or ellipsoid.
Thallus crustaceous 2. *Leprocollema Wain.
Thallus largely squamulose-fruticose.
Apothecia lecideine
(dark-coloured) 3. *Leciophysma Th. Fr.
Apothecia lecanorine 4. Physma Massal.
Spores variously septate or muriform.
Apothecia biatorine
(light-coloured) 5. *Homothecium Mont.
Apothecia lecanorine 6. Collema Wigg.
Thallus with cortex of plectenchyma.
Spores simple.
Spores globose 7. Lemmopsis A. Zahlbr.
Spores ellipsoid, with thick
subverrucose wall 8. *Dichodium Nyl.
Spores vermiform, spirally curved 9. *Koerberia Massal.
Spores variously septate or muriform.
Apothecia biatorine
(light-coloured) 10. *Arctomia Th. Fr.
Apothecia lecanorine 11. Leptogium S. F. Gray.
XL. _HEPPIACEAE_
A family belonging to the “blue-green” series as it is associated with
a gelatinous alga, _Scytonema_, but is of almost entirely cellular
structure and is non-gelatinous. The thallus is squamulose or minutely
foliose, or is formed of narrow almost fruticose lobes; the apothecia are
semi-immersed; the asci are 4-many-spored.
_Heppia_ is a wide-spread genus both in northern and tropical regions
with about forty species that live on soil or rock. So far, no
representative has been recorded in our Islands.
Spores simple, colourless, globose or
ellipsoid 1. *Heppia Naeg.
Spores muriform, colourless, ellipsoid 2. *Amphidium[1054] Nyl.
XLI. _PANNARIACEAE_
The members of this family are also non-gelatinous, though for the
most part associated with blue-green gelatinous algae, _Nostoc_ or
_Scytonema_. The gonidia are bright-green in the genera _Psoroma_ and
_Psoromaria_, the former often included under _Lecanora_, but too closely
resembling _Pannaria_ to be dissociated from that genus.
The thallus varies from being crustaceous to squamulose or foliose, and
has a cortex of plectenchyma on the upper and sometimes also on the lower
surface. The apothecia are superficial or lateral and with or without a
thalline margin (lecanorine or biatorine), the spores are colourless.
Zahlbruckner has included _Hydrothyria_ in this family. It is a
monotypic aquatic genus found in North America and very closely allied
to _Peltigera_. The British species of the genus, familiarly known as
_Coccocarpia_, have been placed under _Parmeliella_, the former name
being restricted to the tropical or subtropical species first assigned
to _Coccocarpia_ and distinguished by the cortex, the hyphae forming it
lying parallel with the surface though forming a regular plectenchyma.
An Antarctic lichen _Thelidea corrugata_ with _Palmella_ gonidia is
doubtfully included: the thallus is foliose, the apothecia biatorine with
colourless 1-septate spores.
Thallus with bright-green gonidia.
With _Palmella_ 1. *Thelidea Hue.
With Protococcaceae.
Apothecia non-marginate (biatorine) 2. *Psoromaria Nyl.
Apothecia marginate 3. Psoroma Nyl.
Thallus with _Scytonema_ gonidia.
Apothecia marginate, spores 1-septate 4. Massalongia Koerb.
Apothecia non-marginate; spores simple.
Upper surface smooth 5. *Coccocarpia Pers.
Upper surface felted 6. *Erioderma Fée.
Thallus with _Nostoc_ gonidia.
Apothecia marginate; spores simple 7. Pannaria Del.
Apothecia non-marginate; spores various.
Thallus crustaceous or minutely
squamulose 8. Placynthium Ach.
Thallus squamulose, cortex
indistinct 9. *Lepidocollema Wain.
Thallus squamulose or foliose,
cortex cellular 10. Parmeliella Müll.-Arg.
Thallus foliose, thin veined
below 11. *Hydrothyria Russ.
XLII. _STICTACEAE_
Thallus foliose, mostly horizontal, with a plectenchymatous cortex
on both surfaces, a tomentum of hair-like hyphae taking the place of
rhizinae on the lower surface. Algal cells Protococcaceae or _Nostoc_.
Cephalodia and cyphellae or pseudocyphellae often present. Apothecia
superficial or lateral; spores colourless or brown, variously septate.
The highly organized cortex and the presence of aeration organs—cyphellae
or pseudocyphellae—which are almost solely confined to the genus _Sticta_
give this family a high position as regards vegetative development. The
two genera are of wide distribution, but _Sticta_ is more abundant in the
Southern Hemisphere. _Lobaria pulmonaria_ is one of our largest lichens.
Under surface dotted with cyphellae
or pseudocyphellae 1. Sticta Schreb.
Under surface without these organs 2. Lobaria Schreb.
XLIII. _PELTIGERACEAE_
A family of heteromerous foliose lichens containing in some instances
blue-green (_Nostoc_), in others bright-green (Protococcaceae) gonidia,
and thus representing a transition between these two series. They have
large or small lobes and grow on the ground or on trees.
Cephalodia, either ectotrophic (Peltidea) or endotrophic (Solorina),
occur in the family and further exemplify the capacity of the fungus
hyphae to combine with different types of algae.
The upper surface is a wide cortex of plectenchyma, which in some forms
(_Nephromium_) is continued below. In the non-corticate under surface
of _Peltigera_, the lower hyphae grow out in hairs or rhizinae, very
frequently brown in colour. Intercalary growth of the upper tissues
stretches the thallus and tears apart the lower under surface so that
the hair-bearing areas become a network of veins, with the white
exposed medulla between. In _Peltigera canina_ there is further growth
and branching of the hyphae in the veins, adding to the bulk of the
interlacing ridges.
From all other foliose lichens Peltigeraceae are distinguished by the
flat wholly appressed or peltate apothecia without a thalline margin
which arise mostly on the upper surface, but in _Nephromium_ on the
extreme margin of the under surface, the tip of the fertile lobe in
that case is turned back as the apothecium matures, so that the fruit
eventually faces the light. In _Nephroma_ has been included _Eunephroma_
with bright-green gonidia and _Nephromium_ with blue-green.
Bitter[1055] has recorded the finding of apothecia on the under surface
of _Peltigera malacea_ and not at the margin, as in _Nephromium_. The
plant was otherwise normal and healthy. _Solorinella_, from Central
Europe and _Asteristion_ from Ceylon are monotypic genera with poorly
developed thalli.
Thallus poorly developed.
Asci 6-8-spored; spores 3-5-septate 1. *Asteristion Leight.
Asci many-spored; spores 1-septate 2. *Solorinella Anzi.
Thallus generally well developed.
Apothecia superficial, sunk in the
thallus 3. Solorina Ach.
Apothecia terminal on upper surface
of lobes 4. Peltigera Willd.
Apothecia terminal on lower surface
of lobes 5. Nephroma Ach.
XLIV. _PERTUSARIACEAE_
Thallus crustaceous, often rather thick and with an amorphous cortex on
the upper surface. Algal cells Protococcaceae. Apothecia solitary or
several immersed in thalline warts, generally with a narrow opening which
barely exposes the disc, and which in one genus, _Perforaria_, is so
small as almost to constitute a perithecium; spores are often very large
and with thick walls; some if not all are multinucleate and germinate at
many points.
In the form of the fruit, this family stands between Pyrenocarpeae and
Gymnocarpeae, though more akin to the latter. _Perforaria_, with two
species, belongs to New Zealand and Japan. _Pertusaria_ has a world-wide
distribution, and _Varicellaria_, a monotypic genus, with a very large
two-celled spore, is an Alpine plant, recorded from Europe and from
Antarctic America.
Spores simple.
Apothecia with pore-like opening 1. *Perforaria Müll.-Arg.
Apothecia with a wider opening 2. Pertusaria DC.
Spores 1-septate 3. Varicellaria Nyl.
XLV. _LECANORACEAE_
Thallus mostly crustaceous, occasionally squamulose or very rarely
minutely fruticulose. The squamulose thallus is corticate above,
the under surface appressed and attached to the substratum by
penetrating hyphae, often effigurate at the circumference. Algal cells
Protococcaceae. Apothecia well distinguished by the thalline margin;
spores colourless, simple or variously septate or muriform.
_Lecanora_, _Ochrolechia_, _Lecania_, _Haematomma_ and _Phlyctis_ are
cosmopolitan genera, some of them with a very large number of species;
the other genera are more restricted in distribution and generally with
few species.
The genus _Candelariella_ is of uncertain position; the spores are 8
or many in the ascus and are simple or 1-septate, and not unfrequently
become polarilocular as in Caloplacaceae, but there is no parietin
present.
Algae distributed through the thallus.
Spores simple 1. *Harpidium Koerb.
Algae restricted to a definite zone.
Spores simple.
Thallus grey, white or yellowish.
Spores rather small 2. Lecanora Ach.
Spores large 3. Ochrolechia Massal.
Thallus bright yellow.
Spores simple or 1-septate 4. Candelariella Müll.-Arg.
Spores 1-septate (rarely pluri-septate).
Paraphyses free.
Thallus squamulose, effigurate 5. Placolecania Zahlbr.
Thallus crustaceous.
Apothecial disc brownish 6. Lecania Zahlbr.
Apothecial disc flesh-coloured 7. Icmadophila Trevis.
Paraphyses branched, intricate 8. *Calenia Müll.-Arg.
Spores elongate, pluri-septate.
Apothecia superficial 9. Haematomma Massal.
Apothecia immersed.
Paraphyses free 10. *Phlyctella Müll.-Arg.
Paraphyses branched, intricate 11. *Phlyctidia Müll.-Arg.
Spores muriform.
Apothecia superficial 12. *Myxodictyon Massal.
Apothecia immersed 13. Phlyctis Wallr.
XLVI. PARMELIACEAE
A very familiar family of foliose lichens. Genera and species are
dorsiventral and stratose in structure, though some _Cetrariae_ are
fruticose in habit. Algal cells are Protococcaceae; in _Physcidia_
they are _Palmellae_. In every case the upper surface of the thallus
is corticate and generally of plectenchyma, the lower being somewhat
similar, but in _Heterodea_ and _Physcidia_, monotypic Australasian
genera, the upper cortex is of branching hyphae parallel with the
surface, the lower surface being non-corticate.
The _Parmeliae_ are mostly provided with abundant rhizinae; in
_Cetrariae_ and _Nephromopsis_ these are very sparingly present, while
in _Anzia_ (including _Pannoparmelia_) the medulla passes into a wide
net-like structure of anastomosing hyphae.
In _Heterodea_, cyphellae occur on the under surface as in Stictaceae;
and in _Cetraria islandica_ bare patches have been described as
pseudocyphellae. The latter lichen is one of the few that are of value as
human food. Special aeration structures are present on the upper cortex
of _Parmelia aspidota_.
Thallus non-corticate below.
Apothecia terminal 1. *Heterodea Nyl.
Apothecia superficial 2. *Physcidia Tuck.
Thallus spongy below 3. *Anzia Stizenb.
Thallus corticate below.
Asci poly-spored 4. Candelaria Massal.
Asci 8-spored.
Spermatia acrogenous 5. Parmeliopsis Nyl.
Spermatia pleurogenous.
Apothecia superficial 6. Parmelia Ach.
Apothecia lateral.
Apothecia on upper surface 7. Cetraria Ach.
Apothecia on lower surface 8. *Nephromopsis Müll.-Arg.
XLVII. _USNEACEAE_
This also is a familiar family of lichens, _Usnea barbata_ the “bearded
moss” being one of the first lichens noted and chronicled. Algal cells
Protococcaceae. Structure radiate, the upright or pendulous habit
characteristic of the family securing all-round illumination. Special
adaptations of the cortex or of the internal tissues have been evolved to
strengthen the thallus against the strains incidental to their habit of
growth as they are attached in nearly all cases by one point only, by a
special sheath, or by penetrating hold-fasts.
Apothecia are superficial or marginal and sometimes shortly stalked;
spores are simple or variously septate.
_Ramalina_ and _Usnea_, the most numerous, are cosmopolitan genera;
_Alectoria_ inhabits northern or hilly regions.
The genus _Evernia_, also cosmopolitan, represents a transition between
foliose and fruticose types; the fronds of the two species, though
strap-shaped and generally upright, are dorsiventral and stratose, the
gonidia for the most part lying beneath one surface; the other (lower)
surface is either white or very dark-coloured. _Everniopsis_, formed of
thin branching strap-shaped fronds, is also dorsiventral.
A number of genera, _Thamnolia_, _Siphula_, etc. are of podetia-like
structure, generally growing in swards. Several of them have been
classified with _Cladoniae_, but they lack the double thallus.
One of these, _Endocena_, a sterile monotypic Patagonian lichen,
with stiff hollow coralloid fronds, was classified by Hue[1056]
along with _Siphula_; recently he has transferred it to his family
Polycaulionaceae[1057] based on _Polycauliona regale_ (_Placodium
frustulosum_ Darbish.), and allied to _Placodium_ Sect. _Thamnoma_[1058].
In recent studies Hue has laid most stress on thalline characters.
He places the new family between “Ramalinaceae” and “Alectoriaceae.”
_Dactylina arctica_ is a common Arctic soil-lichen.
Thallus strap-shaped.
Structure dorsiventral.
Greyish-green above 1. Evernia Ach.
Whitish-yellow above 2. *Everniopsis Nyl.
Structure radiate alike on both surfaces.
Fronds grey; medulla of loose hyphae 3. Ramalina Ach.
Fronds yellow; medulla traversed by
strands 4. *Letharia A. Zahlbr.
Thallus filamentous.
Medulla a strong “chondroid” strand 5. Usnea Dill.
Medulla of loose hyphae.
Spores simple 6. Alectoria Ach.
Spores muriform, brown 7. *Oropogon Fr.
Thallus of upright podetia-like fronds.
Fronds rather long (about two inches),
tapering, white 8. Thamnolia Ach. (Cerania
S. F. Gray).
Fronds shorter, blunt.
Medulla solid 9. *Siphula Fr.
Medulla partly or entirely hollow.
Fronds swollen and tall (about two
inches) 10. *Dactylina Nyl.
Fronds coralloid, entangled 11. *Endocena Cromb.
Fronds short, upright 12. *Dufourea Nyl.
XLVIII. _CALOPLACACEAE_
In this family Zahlbruckner has included the squamulose or crustaceous
lichens with colourless polarilocular spores, relegating those with more
highly developed thallus or with brown spores to other families. He has
also substituted the name _Caloplaca_ for the older _Placodium_, the
latter being, as he considers, less well defined.
Algal cells are Protococcaceae. The thallus is mostly light-coloured,
generally some shade of yellow, and, with few exceptions, contains
parietin, which gives a purple colour on the application of potash. The
squamulose forms are closely appressed to the substratum, and have often
a definite rounded outline (effigurate). The spores have a thick median
septum with a loculus at each end and a connecting canal[1059].
In _Blastenia_ the outer thalline margin is obscure or absent—though
gonidia are frequently present below the hymenium. Caloplacaceae occur
all over the globe; they are among the most brilliantly coloured of all
lichens. _Polycauliona_ Hue[1060] possibly belongs here: though based
on thalline rather than on spore characters, one species at least has
polarilocular spores.
Apothecia with a distinct thalline margin 1. Caloplaca Th. Fr.
Apothecia without a thalline margin 2. Blastenia Th. Fr.
XLIX. _TELOSCHISTACEAE_
Polarilocular colourless spores are the distinguishing feature of this
family as of the Caloplacaceae. Algal cells Protococcaceae. The thallus
of Teloschistaceae is more highly developed, being either foliose or
fruticose, though never attaining to very large dimensions. The cortex
of _Xanthoria_ (foliose) is plectenchymatous, that of _Teloschistes_
(fruticose) is fibrous. The species of both genera are yellow or
greenish-yellow due to the presence of the lichen-acid parietin.
Both genera have a wide distribution over the globe, more especially in
maritime regions.
Thallus foliose 1. Xanthoria Th. Fr.
Thallus fruticose 2. Teloschistes Norm.
L. _BUELLIACEAE_
A family of crustaceous lichens distinguished by the brown two-celled
spores. Algal cells Protococcaceae. Zahlbruckner has included here
_Buellia_ and _Rinodina_; the former with a distinctly lecideine fruit
and with thinly septate spores; the latter lecanorine and with spores
of the polarilocular type, with a very wide central septum pierced in
most of the species by a canal which may or may not traverse the middle
lamella of the wall. _Rinodina_ is closely allied to Physciaceae, while
_Buellia_ has more affinity with Lecideaceae and is near to _Rhizocarpon_.
Both genera are of world-wide distribution.
Apothecia lecideine, without a thalline
margin 1. Buellia De Not.
Apothecia lecanorine, with a thalline
margin 2. Rinodina Massal.
LI. _PHYSCIACEAE_
Thallus foliose or partly fruticose, and generally attached by rhizinae.
Algal cells Protococcaceae. The spores resemble those of _Rinodina_,
dark-coloured with a thick septum and reduced cell-lumina. As in that
species there may be a second septum in each cell, giving a 3-septate
spore; but that is rare.
_Pyxine_, a tropical or subtropical genus, is lecanorine only in the
very early stages; it soon loses the thalline margin. _Anaptychia_ is
differentiated from _Physcia_ by the subfruticose habit, though the
species are nearly all dorsiventral in structure, only a few of them
being truly radiate and corticate on both surfaces. The upper cortex
of _Anaptychia_ is fibrous, but that character appears also in most
species of _Physcia_ either on the upper or the lower side. _Physcia_ and
_Anaptychia_ are widely distributed.
Thalline margin absent in apothecia 1. *Pyxine Nyl.
Thalline margin present in apothecia.
Thallus foliose 2. Physcia Schreb.
Thallus fruticose 3. Anaptychia Koerb.
C. *HYMENOLICHENS
Fungus a Basidiomycete, akin to _Thelephora_. Algal cells _Scytonema_
or _Chroococcus_. Thallus crustaceous, squamulose or foliose. Spores
colourless, produced on basidia, on the under surface of the free thallus.
The Hymenolichens[1061] are few in number and are endemic in tropical or
warm countries. They inhabit soil or trees.
Thallus of extended lobes.
Gonidia near the upper surface 1. *Dictyonema Zahlbr.
Gonidia in centre of tissue 2. *Cora Fr.
Thallus squamulose, irregular 3. *Corella Wain.
II. NUMBER AND DISTRIBUTION OF LICHENS
1. ESTIMATES OF NUMBER
Calculations have been made and published, once and again, as to the
number of lichen species occurring over the globe or in definite areas.
In 1898 Fünfstück stated that about 20,000 different species had been
described, but as many of them had been proved to be synonyms, and since
many must rank as forms or varieties, the number of well-authenticated
species did not then, according to his estimate, exceed 4000. Many
additional genera and species have, however, been discovered since then.
In Engler and Prantl’s _Pflanzenfamilien_, over 50 families and nearly
300 genera find a place, but even in these larger groupings opinions
differ as to the limits both of genera and families, and lichenologists
would not all accept the arrangement given in that volume.
Fünfstück has reckoned that of his estimated 4000, about 1500 are
European and of these at least 1200 occur in Germany. Probably this is
too low an estimate for that large country. Leighton in 1879 listed, in
his _British Lichen Flora_, 1710 in all, and, as the compilation includes
varieties, it cannot be considered as very far astray. On comparing it
with Olivier’s[1062] recent statistics of lichens, we find that of the
larger fruticose and foliose species, 310 are recognized by him for the
whole of Europe, 206 of these occurring in the British Isles. Leighton’s
estimate of similar species is about 145, without including varieties now
reckoned as good species. In a more circumscribed area, Th. Fries[1063]
described for Spitzbergen about 210 different lichens, a number that
closely approximates to the 206 recent records by Darbishire[1064] for
the same area.
A general idea of the comparative numbers of the different types of
lichens may be gathered from Hue’s compilation of exotic lichens[1065],
examined or described by Nylander, and now in the Paris herbarium.
There are 135 genera with 3686 species. Of these, about 829 belong to
the larger foliose and fruticose lichens (including _Cladoniae_); the
remaining 2857 belong to the smaller kinds, most of them crustaceous.
2. GEOGRAPHICAL DISTRIBUTION
A. GENERAL SURVEY
The larger foliose and fruticose lichens are now fairly well known and
described for Europe, and the knowledge of lichens in other continents
is gradually increasing. It is the smaller crustaceous forms that baffle
the investigator. The distribution of all lichens over the surface of the
earth is controlled by two principal factors, climate and substratum; for
although lichens as a rule require only support, they are most of them
restricted to one or another particular substratum, either organic or
inorganic. As organisms which develop slowly, they require an unchanging
substratum, and as sun-plants they avoid deeply shaded woodlands: their
occurrence thus depends to a large extent on the configuration and
general vegetation of the country.
Though so numerous and so widely distributed, lichens have not evolved
that great variety of families and genera characteristic of the allied
fungi and algae. They conform to a few leading types of structure,
and thus the Orders and Families are comparatively few, and more or
less universal. They are most of them undoubtedly very old plants and
were probably wide-spread before continents and climates had attained
their present stability. Arnold[1066] indeed considers that a large
part of the present-day lichens were almost certainly already evolved
at the end of the Tertiary period, and that they originated in a warm
or probably subtropical climate. As proof of this he cites such genera
as _Graphis_, _Thelotrema_ and _Arthonia_[1067] which are numerous in
the tropics though rare in the colder European countries; and he sees
further proof in the fact that many fruticose and gelatinous lichens do
not occur further north than the forest belt, though they are adapted
to cold conditions. Several genera that are abundant in the tropics are
represented outside these regions by only one or few species, as for
instance _Conotrema urceolatum_ and _Bombyliospora incana_.
During the Ice age of the Quaternary period, not many new species can
have arisen, and such forms as were not killed off must have been driven
towards the south. As the ice retreated the valleys were again stocked
with southern forms, and northern species were left behind on mountain
tops all over the globe.
In examining therefore the distribution of lichens, it will be found
that the distinction between different countries is relative, certain
families being more or less abundant in some regions than others, but,
in general, nearly all being represented. Certain species are universal,
where similar conditions prevail. This is especially true of those
species adapted to extreme cold, as that condition, normal in polar
regions, recurs even on the equator if the mountains reach the limit of
perpetual snow; the vertical distribution thus follows on the lines of
the horizontal.
In all the temperate countries we find practically the same families,
with some few exceptions; there is naturally more diversity of genera
and species. Genera that are limited in locality consist, as a rule,
of one or few species. In this category, however, are not included the
tropical families or genera which may be very rich in species: these are
adapted to extreme conditions of heat and often of moisture, and cannot
exist outside tropical or subtropical regions, extreme heat being more
restricted as to geographical position than extreme cold.
In the study of distribution the question which arises as to the place
of origin of such widely distributed plants is one that is difficult to
solve. Wainio[1068] has attempted the task in regard to _Cladonia_, one
of the most unstable genera, the variations of form, which are dependent
on external circumstances, being numerous and often bewildering. In his
fine monograph of the genus, 132 species are described and 25 of these
are cosmopolitan.
The distribution of Phanerogams is connected, as Wainio points out, with
causes anterior to the present geological era, but this cannot be the
case in a genus so labile and probably so recent as _Cladonia_, though
some of the species have existed long enough to spread and establish
themselves from pole to pole. Endemic species, or those that are confined
to a comparatively limited area, are easily traced to their place of
origin, that being generally the locality where they are found in most
abundance, and as a general rule in the centre of that area, though there
may be exceptions: a plant for instance that originated on a mountain
would migrate only in one direction—towards the regions of greater cold.
The difficulty of determining the primitive stations of cosmopolitan,
or of widely spread, species is much greater, but generally they also
may be referred to their area of greatest abundance. Thus a species
may occur frequently in one continent and but rarely in another, even
where the conditions of climate, etc., are largely comparable. It may
therefore be inferred that the plant has not yet reached the full extent
of possible distribution in the less frequented area. As examples of
this, Wainio cites, among other instances, _Cladonia papillaria_, which
has a very wide distribution in Europe, but, as yet, has been found only
in the eastern parts of North America; and _Cl. pycnoclada_, a plant
which braves the climate of Cape Horn and the Falkland Islands, but has
not travelled northward beyond temperate North America: the southern
origin of that species is thus plainly indicated. Wainio also finds that
evidence of the primitive locality of a very widely spread species may be
obtained by observing the locality of species derived from it, which are
as yet of limited distribution; presumably these arose in the ancestral
place of origin, though this indication is not always to be relied on.
If, however, the ancestral plant has given rise to several of these
rarer related species, those of them that are most closely allied to the
primitive plant would be found near to it in the original locality.
A detailed account of species distribution according to these indications
is given by Wainio and is full of interest. No such attempt has been
made to deal with any other group, and the distribution of genera and
species can only be suggested. An exhaustive comparison of the lichens
of different regions is beyond the purpose of our study and is indeed
impossible as, except in some limited areas, or for certain species,
the occurrence and distribution are not fully known. It is in any case
only tentatively that genera or species can be described as local or
rare, until diligent search has been made for them over a wider field.
The study of lichens from a floristic point of view lags behind that of
most other groups of plants. The larger lichen forms have received more
attention, as they are more evident and more easily collected; but the
more minute species are not easily detected, and, as they are largely
inseparable from their substratum of rocks, or trees, etc., on which
they grow, they are often difficult to collect. They are also in many
instances so indefinite, or so alike in outward form, that they are
liable to be overlooked, only a microscopic examination revealing the
differences in fruit and vegetative structure.
Though much remains to be done, still enough is known to make the
geographical distribution of lichens a subject of extreme interest. It
will be found most instructive to follow the usual lines of treatment,
which give the three great divisions: the Polar, the Temperate and the
Tropical regions of the globe.
B. LICHENS OF POLAR REGIONS
Strictly speaking, this section should include only lichens growing
within the Polar Circles; but in practice the lichens of the whole of
Greenland and those of Iceland are included in the Arctic series, as
are those of Alaska: the latitudinal line of demarcation is not closely
adhered to. With the northern lichens may also be considered those of the
Antarctic continent, as well as those of the islands just outside the
Antarctic Circle, the South Shetlands, South Orkneys, Tierra del Fuego,
South Georgia and the Falkland Islands. During the Glacial period, the
polar forms must have spread with the advancing cold; as the snow and ice
retreated, these forms have been left, as already stated, on the higher
colder grounds, and representatives of polar species are thus to be found
very far from their original haunts. There are few exclusively boreal
genera: the same types occur at the Poles as in the higher subtemperate
zones. One of the most definitely polar species, for instance, _Usnea_
(_Neuropogon_) _melaxantha_ grows in the whole Arctic zone, and, in the
Antarctic, is more luxuriant than any other lichen, but it has also been
recorded from the Andes in Chili, Bolivia and Peru, and from New Zealand
(South Island).
Cold winds are a great feature of both poles, and the lichens that by
structure or habit can withstand these are the most numerous; those that
have a stout cortical layer are able to resist the low temperatures, or
those that grow in tufts and thus secure mutual protection. In Arctic
and Subarctic regions, 495 lichens have been recorded, most of them
crustaceous. Among the larger forms the most frequently met are certain
species of _Peltigera_, _Parmelia_, _Gyrophora_, _Cetraria_, _Cladonia_,
_Stereocaulon_ and _Alectoria_. Among smaller species _Lecanora tartarea_
spreads everywhere, especially over other vegetation, _Lecanora varia_
reaches the farthest limits to which wood, on which it grows, has
drifted, and several species of _Placodium_ occur constantly, though not
in such great abundance. Over the rocks spread also many crustaceous
Lecideaceae too numerous to mention, one of the most striking being the
cosmopolitan _Rhizocarpon geographicum_.
Wainio[1069] has described the lichens collected by Almquist at Pitlekai
in N.E. Siberia just on the borders of the Arctic Circle, and he gives a
vivid account of the general topography. The snow lies on the ground till
June and falls again in September, but many lichens succeed in growing
and fruiting. It is a region of tundra and sand, strewn more or less with
stones. Most of the sand is bare of all vegetation; but where mosses,
etc., have gained a footing, there are also a fair number of lichens:
_Lecanora tartarea_, _Psoroma hypnorum_, with _Lecideae_, _Parmeliae_,
_Cladoniae_, _Stereocaulon alpinum_, _Solorina crocea_, _Sphaerophorus
globosus_, _Alectoria nigricans_ and _Gyrophora proboscidea_. Some
granite rocks in that neighbourhood rise to a height of 200 ft., and
though bare of vegetation on the north side, yet, in sheltered nooks,
several species are to be found. Stunted bushes of willow grow here
and there, and on these occur always the same species: _Placodium
ferrugineum_, _Rinodina archaea_, _Buellia myriocarpa_ and _Arthopyrenia
punctiformis_. Some species such as _Sphaerophorus globosus_, _Dactylina
arctica_ (a purely Arctic genus and species) and _Thamnolia vermicularis_
are so abundant that they bulk as largely as other better represented
genera such as _Cladoniae_, _Lecanorae_ or _Lecideae_. On the soil,
_Lecanorae_ cover the largest areas.
Wainio determined a large number of lichens with many new species, but
the region is colder than that of Lappland, and trees with tree-lichens
are absent, with the exception of those given above. In Arctic Siberia,
Elenkin[1070] discovered a new lichen _Placodium subfruticulosum_
which scarcely differs from Darbishire’s[1071] Antarctic species _Pl.
fruticulosum_ (or _P. regale_); both are distinguished by the fruticose
growth of the thallus, for which reason Hue[1072] placed them in a new
genus, _Polycauliona_.
The Antarctic Zone and the neighbouring lands are less hospitable to
plant life than the northern regions, and there is practically no
accumulation of detritus. Collections have been made by explorers, and
several lists have been published which include a marvellous number of
species common to both Poles, if the subantarctic lands are included in
the survey. An analytic study of the various lists has been published
by Darbishire[1073]. He recognizes 106 true Antarctic lichens half of
which are Arctic as well. The greater number are crustaceous and are
plants common also to other lands though a certain number are endemic.
The most abundant genera in species as well as individuals are _Lecidea_
and _Lecanora_. Several bright yellow species of _Placodium_—_Pl.
elegans_, _Pl. murorum_, etc., are there as at the North Pole. Among
the larger forms, _Parmeliae_, _Cetrariae_, and _Cladoniae_ are fairly
numerous; _Usneae_ and _Ramalinae_ rather uncommon, while members of the
Stictaceae are much more abundant than in the North. The common species
of _Peltigera_ also occur in Antarctica, though _P. aphthosa_ and _P.
venosa_ are wanting; both of these latter are boreal species. Darbishire
adds that lichens have so great a capacity to withstand cold, that they
are only checked by the snow covering, and were bare rocks to be found
at the South Pole, he is sure lichens would take possession of them.
The most southerly point at which any plant has been found is 78° South
latitude and 162° East longitude, in which locality the lichen _Lecanora
subfusca_ was collected by members of Scott’s Antarctic expedition
(1901-1904) at a height of 5000 ft.
A somewhat different view of the Antarctic lichen flora is indicated by
Hue[1072] in his account of the plants brought back by the second French
Antarctic Expedition. The collection was an extremely favourable and
important one: great blocks of stone with their communities of lichens
were secured, and these blocks were entirely covered, the crustaceous
species, especially, spreading over every inch of space.
Hue determined 126 species, but as 15 of these came from the Magellan
regions only 111 were truly Antarctic. Of these 90 are new species, 29
of them belonging to the genus _Buellia_. Hue considers, therefore, that
in Antarctica there is a flora that, with the exception of cosmopolitan
species, is different from every other, and is special to these southern
regions. Darbishire himself described 34 new Antarctic species, but only
10 of these are from true Antarctica; the others were collected in South
Georgia, the Falkland Islands or Tierra del Fuego. Even though many
species are endemic in the south, the fact remains that a remarkable
number of lichens which occur intermediately on mountain summits are
common to both Polar areas.
C. LICHENS OF THE TEMPERATE ZONES
Regions outside the Polar Circles which enjoy, on the whole, cool
moist climates, are specially favourable to lichen growth, and the
recorded numbers are very large. The European countries are naturally
those in which the lichen flora is best known. Whereas polar and high
Alpine species are stunted in growth and often sterile, those in milder
localities grow and fruit well, and the more highly developed species are
more frequent. _Parmeliae_, _Nephromae_, _Usneae_ and _Ramalinae_ become
prominent, especially in the more northern districts. Many Arctic plants
are represented on the higher altitudes. A comparison has been made
between the lichens of Greenland and those of Germany: of 286 species
recorded for the former country, 213 have been found in Germany, the
largest number of species common to both countries being crustaceous.
Lindsay[1074] considered that Greenland lichens were even more akin to
those of Scandinavia.
There is an astonishing similarity of lichens in the Temperate Zone
all round the world. Commenting on a list of Chicago lichens by
Calkins[1075], Hue[1076] pointed out that with the exception of a
few endemic species they resemble those of Normandy. The same result
appears in Bruce Fink’s[1077] careful compilation of Minnesota lichens,
which may be accepted as typical of the Eastern and Middle States of
North Temperate America. The genera from that region number nearly 70,
and only two of these, _Omphalaria_ and _Heppia_, are absent from our
British Flora. The species naturally present much greater diversity.
Very few Graphideae are reported. In other States of North America there
occurs the singular aquatic lichen, _Hydrothyria venosa_, nearly akin to
_Peltigera_.
If we contrast American lichens with these collected in South Siberia
near Lake Baikal[1078], we recognize there also the influence of
temperate conditions. Several species of _Usnea_ are listed, _U.
barbata_, _U. florida_, _U. hirta_ and _U. longissima_, all of them
also American forms, _U. longissima_ having been found in Wisconsin.
_Xanthoria parietina_, an almost cosmopolitan lichen, is absent from
this district, and is not recorded from Minnesota. The opinion[1079] in
America is that it is a maritime species: Tuckerman gives its habitat
as “the neighbourhood of a great water,” and reports it from near Lake
Superior. In our country it grows at a good distance from the sea, in
Yorkshire dales, etc., but all our counties would rank as maritime in the
American sense. _Lecanora tartarea_ which is rare in Minnesota is also
absent from the Lake Baikal region. It occurs frequently both in Arctic
and in Antarctic regions, and is probably also somewhat maritime in
habitat. Many of the _Parmeliae_, _Nephromiae_ and _Peltigerae_, common
to all northern temperate climes, are Siberian as are also _Cladoniae_
and many crustaceous species. There is only one _Sticta_, _St. Wrightii_,
a Japanese lichen, recorded by Wainio from this Siberian locality.
A marked difference as regards species is noted between the Flora of
Minnesota and that of California. Herre[1080] has directed attention to
the great similarity between the lichens of the latter state and those
of Europe: many European species occur along the coast and nowhere else
in America so far as is yet known; as examples he cites, among others,
_Calicium hyperellum_, _Lecidea quernea_, _L. aromatica_, _Gyrophora
polyrhiza_, _Pertusaria amara_, _Roccella fuciformis_, _R. fucoides_
and _R. tinctoria_. The Scandinavian lichen, _Letharia vulpina_, grows
abundantly there and fruits freely; it is very rare in other parts of
America. Herre found, however, no specimens of _Cladonia rangiferina_,
_Cl. alpestris_ or _Cl. sylvatica_, nor any species of _Graphis_; he
is unable to explain these anomalies in distribution, but he considers
that the cool equable climate is largely responsible: it is so much more
like that of the milder countries of Europe than of the states east
of the Sierra Nevada. His contention is supported by a consideration
of Japanese lichens. With a somewhat similar climate there is a great
preponderance of European forms. Out of 382 species determined by
Nylander[1081], 209 were European. There were 17 _Graphideae_, 31
_Parmeliae_, and 23 _Cladoniae_, all of the last named being European.
These results of Nylander’s accord well with a short list of 30 species
from Japan compiled by Müller[1082] at an earlier date. They were chiefly
crustaceous tree-lichens; but the _Cladoniae_ recorded are the familiar
British species _Cl. fimbriata_, _Cl. pyxidata_ and _Cl. verticillata_.
With the Japanese Flora may be compared a list[1083] of Maingay’s lichens
from China, 35 in all. _Collema limosum_, the only representative
of Collemaceae in the list, is European, as are the two species of
_Ramalina_, _R. gracilenta_ and _R. pollinaria_; four species of
_Physcia_ are European, the remaining _Ph. picta_ being a common
tropical or subtropical plant. _Lecanora saxicola_, _L. cinerea_,
_Placodium callopismum_ and _Pl. citrinum_ are cosmopolitan, other
_Lecanorae_ and most of the _Lecideae_ are new. _Graphis scripta_,
_Opegrapha subsiderella_ and _Arthonia cinnabarina_—the few Graphideae
collected—are more or less familiar home plants. Among the Pyrenocarpei,
_Verrucaria_ (_Pyrenula_) _nitida_ occurs; it is a widely distributed
tree-lichen.
It is unnecessary to describe in detail the British lichens. Some
districts have been thoroughly worked, others have barely been touched.
The flora as a whole is of a western European type showing the influence
of the Gulf Stream, though there is also a representative boreal growth
on the moorlands and higher hills, especially in Scotland. Such species
as _Parmelia pubescens_, _P. stygia_ and _P. alpicola_ recall the Arctic
Circle while _Alectoriae_, _Cetrariae_ and _Gyrophorae_ represent
affinity with the colder temperate zone.
In the southern counties such species as _Sticta aurata_, _S.
damaecornis_, _Phaeographis Lyellii_ and _Lecanora_ (_Lecania_)
_holophaea_ belong to the flora of the Atlantic seaboard, while in
S.W. Ireland the tropical genera _Leptogidium_ and _Anthracothecium_
are each represented by a single species. The tropical or subtropical
genus _Coenogonium_ occurs in Great Britain and in Germany, with one
sterile species, _C. ebeneum_. _Enterographa crassa_ is another of our
common western lichens which however has travelled eastwards as far as
Wiesbaden. _Roccella_ is essentially a maritime genus of warm climates:
two species, _R. fuciformis_ and _R. fucoides_, grow on our south and
west coasts. The famous _R. tinctoria_ is a Mediterranean plant, though
it is recorded also from a number of localities outside that region and
has been collected in Australia.
In the temperate zones of the southern hemisphere are situated the great
narrowing projections of South Africa and South America with Australia
and New Zealand. As we have seen, the Antarctic flora prevails more or
less in the extreme southern part of America, and the similarity between
the lichens of that country and those of New Zealand is very striking,
especially in the fruticulose forms. There is a very abundant flora in
the New Zealand islands with their cool moist climate and high mountains.
Churchill Babington[1084] described the collections made by Hooker.
Stirton[1085] added many species, among others _Calycidium cuneatum_,
evidently endemic. Later, Nylander[1086] published the species already
known, and Hellbom[1087] followed with an account of New Zealand lichens
based on Berggsen’s collections; many more must be still undiscovered.
Especially noticeable as compared with the north, are the numbers
of Stictaceae which reach their highest development of species and
individuals in Australasia. They are as numerous and as prominent as are
Gyrophoraceae in the north. A genus of Parmeliaceae, _Hetorodea_, which,
like the _Stictae_, bears cyphellae on the lower surface, is peculiar to
Australia.
A warm current from the tropical Pacific Ocean passes southwards along
the East Coast of Australia, and Wilson[1088] has traced its influence on
the lichens of Australia and Tasmania to which countries a few tropical
species of _Graphis_, _Chiodecton_ and _Trypethelium_ have migrated.
Various unusual types are to be found there also: the beautiful _Cladonia
retepora_ (Fig. 71), which spreads over the ground in cushion-like
growths, with the genera _Thysanothecium_ and _Neophyllis_, genera of
Cladoniaceae endemic in these regions.
The continent of Africa on the north and east is in so close connection
with Europe and Asia that little peculiarity in the flora could be
expected. In comparing small representative collections of lichens, 37
species from Egypt and 20 from Palestine, Müller[1089] found that there
was a great affinity between these two countries. Of the Palestine
species, eight were cosmopolitan; among the crustaceous genera,
_Lecanorae_ were the most numerous. There was no record of new genera.
The vast African continent—more especially the central region—has
been but little explored in a lichenological sense; but in 1895
Stizenberger[1090] listed all of the species known, amounting to
1593, and new plants and new records have been added since that day.
The familiar genera are well represented, _Nephromium_, _Xanthoria_,
_Physcia_, _Parmelia_, _Ramalina_ and _Roccella_, some of them by
large and handsome species. In the Sahara Steiner[1091] found that
genera with blue-green algae such as the Gloeolichens were particularly
abundant; _Heppia_ and _Endocarpon_ were also frequent. Algeria has a
Mediterranean Flora rather than tropical or subtropical. Flagey[1092]
records no species of _Graphis_ for the province of Constantine, and only
22 species of other Graphideae. Most of the 519 lichens listed by him
there are crustaceous species. South America stretches from the Tropics
in the north to Antarctica in the south. Tropical conditions prevail
over the central countries and tropical tree-lichens, Graphidaceae,
Thelotremaceae, etc. are frequent; further West, on the Pacific slopes,
_Usneae_ and _Ramalinae_ hang in great festoons from the branches, while
the foliose _Parmeliae_ and _Stictae_ grow to a large size on the trunks
of the trees.
Wainio’s[1093] _Lichens du Brésil_ is one of the classic systematic books
and embodies the writer’s views on lichen classification. There are no
new families recorded though a number of genera and many species are
new, and, so far as is yet known, these are endemic. Many of our common
forms are absent; thus _Peltigera_ is represented by three species only,
_P. leptoderma_, _P. spuriella_ and _P. Americana_, the two latter being
new species. _Sticta_ (including _Stictina_) includes only five species,
and _Coenogonium_ three. There are 39 species of _Parmelia_ with 33 of
_Lecanora_ and 68 of _Lecidea_, many of them new species.
D. LICHENS OF TROPICAL REGIONS
In the tropics lichens come under the influence of many climates: on the
high mountains there is a region of perpetual snow, lower down a gradual
change to temperate and finally to tropical conditions of extreme heat,
and, in some instances, extreme moisture. There is thus a bewildering
variety of forms. By “tropical” however the warmer climate is always
implied. Several families and genera seem to flourish best in these warm
moist conditions and our familiar species grow there to a large size.
Among crustaceous families Thelotremaceae and Graphidaceae are especially
abundant, and probably originated there. In the old comprehensive genus
_Graphis_, 300 species were recorded from the tropics. It should be
borne in mind that _Trentepohlia_, the alga that forms the gonidia of
these lichens, is very abundant in the tropics. _Coenogonium_, a genus
containing about twelve species and also associated with _Trentepohlia_,
is scarcely found in Europe, except one sterile species, _C. ebeneum_.
Other species of the genus have been recorded as far north as Algeria in
the Eastern Hemisphere and Louisiana in the Western, while one species,
_C. implexum_, occurs in the southern temperate zone in Australia and New
Zealand.
Of exclusively tropical lichens, the Hymenolichens are the most
noteworthy. They include three genera, _Cora_, _Corella_ and
_Dictyonema_, the few species of which grow on trees or on the ground
both in eastern and western tropical countries.
Other tropical or subtropical forms are _Oropogon loxensis_, similar to
_Alectoria_ in form and habit, but with one brown muriform spore in the
ascus; it is only found in tropical or subtropical lands. _Physcidia
Wrightii_ (Parmeliaceae) is exclusively a Cuban lichen. Several small
genera of Pyrenopsidaceae such as _Jenmania_ (British Guiana), _Paulia_
(Polynesia) and _Phloeopeccania_ (South Arabia) seem to be confined to
very hot localities. On the other hand Collemaceae are rare: Wainio
records from Brazil only four species of _Collema_, with nine of
_Leptogium_.
Among Pyrenolichens, Paratheliaceae, Mycoporaceae and Astrotheliaceae are
almost exclusively of tropical distribution, and finally the leaf lichens
with very few exceptions. These follow the leaf algae, _Mycoidea_,
_Phycopeltis_, etc., which are so abundant on the coriaceous long-lived
green leaves of a number of tropical Phanerogams. All the Strigulaceae
are epiphytic lichens. _Phyllophthalmaria_ (Thelotremaceae) is also a
leaf genus; one of the species, _Ph. coccinea_, has beautiful carmine-red
apothecia. The genera of the tropical family Ectolechiaceae also inhabit
leaves, but they are associated with Protococcaceae; one of the genera
_Sporopodium_[1094] is remarkable as having hymenial gonidia. Though
tropical in the main, epiphyllous lichens may spread to the regions
beyond: _Sporopodium Caucasium_ and a sterile _Strigula_ were found by
Elenkin and Woronichin[1095] on leaves of _Buxus sempervirens_ in the
Caucasus, well outside the tropics.
_Pilocarpon_, an epiphytic genus, is associated with Protococcaceae; one
of the species, _P. leucoblepharum_, spreads from the bark to the leaves
of pine-trees; it is widely distributed and has also been reported in the
Caucasus[1096]. _Chrysothrix_, in which the gonidia belong to the algal
genus _Palmella_, grows on Cactus spines in Chili, and may also rank as a
subtropical epiphyllous lichen.
A series of lichens from the warm temperate region of Transcaucasia
investigated by Steiner[1097] were found to be very similar to those
of Central Europe. Lecanoraceae were, however, more abundant than
Lecideaceae and Verrucariaceae were comparatively rare.
Much of Asia lies within tropical or subtropical influences. Several
regions have received some amount of attention from collectors. From
Persia there has been published a list of 59 species determined by
Müller[1098]; several of them are Egyptian or Arabian plants, 15 are new
species, but the greater number are European.
A small collection of 53 species from India, near to Calcutta, published
by Nylander[1099], included a new genus of Caliciaceae, _Pyrgidium_
(_P. bengalense_), allied to _Sphinctrina_. He also recorded _Ramalina
angulosa_ in African species, along with _R. calicaris_, _R. farinacea_
and _Parmelia perlata_, f. _isidiophora_, which are British. Other
foliose forms, _Physcia picta_, _Pyxine Cocoës_ and _P. Meissnerii_ are
tropical or subtropical; along with these were collected crustaceous
tropical species belonging to _Lecanorae_, _Lecideae_, Graphideae, etc.
Leighton[1100] published a collection of Ceylon lichens and found that
Graphideae predominated. Nylander[1101] came to the same conclusion
with regard to lichens referred to him: out of 159 species investigated
from Ceylon, there were 36 species of Graphideae. In another list[1102]
of Labuan, Singapore and Malacca lichens, 164 in all, he found that 56
belonged to the Graphidei, 36 to Pyrenocarpei, 14 to Thelotremei and 11
to Parmelei; only 15 species were European.
On the whole it is safe to conclude from the above and other publications
that the exceptional conditions of the tropics have produced many
distinctive lichens, but that a greater abundance both of species and
individuals is now to be found in temperate and cold climates.
III. FOSSIL LICHENS
In pronouncing on the great antiquity of lichens, proof has been adduced
from physiological rather than from phytogeological evidence. It would
have been of surpassing interest to trace back these plants through the
ages, even if it were never possible to assign to any definite period
the first symbiosis of the fungus and alga; but among fossil plants there
are only scanty records of lichens and even these few are of doubtful
determination.
The reason for this is fairly obvious: not only are the primitive
thalline forms too indistinct for recognizable preservation, but all
lichens are characterized by the gelatinous nature of the hyphal or of
the algal membranes which readily imbibe water. They thus become soft and
flaccid and unfit to leave any impress on sedimentary rocks. It has also
been pointed out by Schimper[1103] that while deciduous leaves with fungi
on them are abundant in fossil beds, lichens are entirely wanting. These
latter are so firmly attached to the rocks or trees on which they grow
that they are rarely dislodged, and form no part of wind- or autumn-fall.
Trunks and branches of trees lose their bark by decay long before they
become fossilized and thus all trace of their lichen covering disappears.
The few records that have been made are here tabulated in chronological
order:
1. PALAEOZOIC. Schimper decides that there are no records of lichens in
the earlier epochs. Any allusions[1104] to their occurrence are held to
be extremely vague and speculative.
2. MESOZOIC. Braun[1105] has recorded a _Ramalinites lacerus_ from the
Keuper sandstone at Eckersdorf, though later[1106] he seemed to be
doubtful as to his determination. One other lichen, an _Opegrapha_, has
been described[1107] from the chalk at Aix.
3. CAINOZOIC. In the brown-coal formations of Saxony Engelhardt[1108]
finds two lichens: _Ramalina tertiaria_, a much branched plant, the
fronds being flat and not channelled “and of further interest that it is
attached to a carbonized stem.” The second form, _Lichen dichotomus_,
has a dichotomously branching strap-shaped frond. “There is sufficient
evidence that these fronds were cylindrical and that the width is due to
pressure. In one place a channel is visible, filled with an ochraceous
yellow substance.”
Other records on brown coal or lignite are: _Verrucarites
geanthricis_[1109] Goepp., somewhat similar to _Pyrenula nitida_, found
at Muskau in Silesia; _Opegrapha Thomasiana_[1110] Goepp., near to
_Opegrapha varia_, and _Graphis scripta succinea_ Goepp.[1111] on a piece
of lignite in amber beds, all of them doubtful.
Schimper has questioned, as he well might, Ludwig’s[1112] records from
lignite from the Rhein-Wetterau Tertiary formations; these are: _Cladonia
rosea_, _Lichen albineus_, _L. diffissus_ and _L. orbiculatus_; he thinks
they are probably fungus mycelia. Another lichen, a _Parmelia_ with
apothecia, which recalls somewhat _P. saxatilis_ or _P. conspersa_,
collected by Geyler also in the brown coal of Wetterau is accepted by
Schimper[1113] as more trustworthy.
More authentic also are the lichens from the amber beds of Königsberg
and elsewhere collected by Goeppert and others. These deposits are
Cainozoic and have been described by Goeppert and Menge[1114] as middle
Miocene. Schimper gives the list as: _Parmelia lacunosa_ Meng. and
Goepp., fragments of thallus near to _P. saxatilis_; _Sphaerophorus
coralloides_; _Cladonia divaricata_ Meng. and Goepp.; _Cl. furcata_;
_Ramalina calicaris_ vars. _fraxinea_ and _canaliculata_; _Cornicularia
aculeata_, _C. subpubescens_ Goepp., _C. ochroleuca_, _C. succinea_
Goepp., and _Usnea barbata_ var. _hirta_. Schimper rather deprecates
specific determinations when dealing with such imperfect fragments.
In a later work Goeppert and Menge[1114] state that they have found
twelve different amber lichens and that among these are _Physcia
ciliaris_, _Parmelia physodes_ and _Graphis_ (probably _G. scripta
succinea_) along with _Peziza resinae_ which is more generally classified
among lichens as _Lecidea_ (_Biatorella_) _resinae_.
Another series of lichens found in recent deposits in North Europe
has been described by Sernander[1115] as “subfossil.” While engaged
on the investigations undertaken by the Swedish Turf-Moor Commission,
he noted the alternation of slightly raised _Sphagnum_ beds with
lower-lying stretches of _Calluna_ and lichen moor—in some instances
dense communities of _Cladonia rangiferina_. In time the turf-forming
_Sphagnum_ overtopped and invaded the drier moorland, covering it with a
new formation of turf. Beneath these layers of “regenerated turf” were
found local accumulations of blackened remains of the _Cladonia_ still
recognizable by the form and branching. Some specimens of _Cetraria
islandica_ were also determined.
Of especial lichenological interest in these northern regions was the
Calcareous Tufa or Calc-sinter in which Sernander also found subfossil
lichens—distinct impressions of _Peltigera_ spp. and the foveolae of
endolithic calcicolous species.
In another category he has placed _Ramalina fraxinea_, _Graphis_ sp. and
_Opegrapha_ sp., traces of which were embedded with drift in the Tufa. In
the two Graphideae the walls of apothecia and pycnidia were preserved.
Sernander considers their presence of interest as testifying to warmer
conditions than now prevail in these latitudes.