THE ORDER COMPOSITÆ: ILLUSTRATED BY THE SUCCORY, THE SOWTHISTLE,
THE DANDELION, THE BURDOCK, THE DAISY, THE CHRYSANTHEMUM, FEVERFEW,
PELLITORY OF SPAIN, WILD CHAMOMILE, TRUE CHAMOMILE, YARROW, THE
BUR-MARIGOLD, GROUNDSEL, RAGWORT, BIRD’s TONGUE, PURPLE JACOBÆA,
CINERARIA, SUNFLOWER, MUTISIA, AND TRIPTILION.
The plants composing the order Compositæ have all compound flowers,
which differ from other flowers as much as a compound leaf does from a
simple one. As the compound leaf is composed of a number of leaflets or
pinnæ united by a common petiole; so a compound flower is composed of a
number of florets, united by a common receptacle, which is surrounded
by a calyx-like involucre, so as to give the whole mass the appearance
of a simple flower. Each floret has a calyx, the tubular part of which
is rarely sufficiently distinct to be perceptible, but the limb is
generally cut into long feathery segments called pappus. The ovary of
each floret contains only one seed; and the fruit, which is called an
achenium, retains the pappus when ripe, and falls without opening.
There are five stamens, the filaments of which are distinct, but the
anthers grow together so as to form a kind of cylinder, through
which passes the style, ending in a two-lobed stigma (see _a_ in
_fig._ 41). Most of the corollas are of two kinds: viz. the ligulate,
as exemplified in the floret of the wild Lettuce (_Lactuca virosa_)
shown in _fig._ 41; and the tubular, as shown in a floret of the
Cotton-thistle (_Onopordium Acanthium_) see _fig._ 42. All the British
species of Compositæ have their florets either entirely of one of these
kinds, or of the two mixed together; but some foreign genera have
florets with two equal lips, cut into three or four lobes, as shown in
a floret of _Mutisia latifolia_, at (_e_), _fig._ 46, p. 108. These
florets are called bilabiate. It will be observed that in all these
examples, as indeed, in all the flowers belonging to the order, that
the pappus (_b_, in _figs._ 41 and 42), is always on the outside of the
corolla, thus plainly indicating its connexion with the calyx.
[Illustration: FIG. 41.—LIGULATE FLORET OF WILD LETTUCE.]
[Illustration: FIG. 42.—TUBULAR FLORET OF THE COTTON-THISTLE.]
The order Compositæ is a very large one, above seven thousand species
having been named and described; and to assist the memory in retaining
the names of this great number of plants, various means have been
devised for dividing the order into sections and tribes. The principal
botanists who have proposed means of arranging this order, are Cassini,
Lessing, and lastly the late Professor De Candolle, in three volumes
of his _Prodromus_ published in 1840. But as the distinctions between
the divisions proposed, lie in the difference found in the stigmas and
pappus of the different genera, I have judged them too troublesome for
my readers, as I am sure they are for myself, and I have preferred
following the plan adopted by Dr. Lindley in his _Elements of Botany_,
published in 1841, and dividing the Compositæ into four tribes; viz.,
the three originally proposed by Jussieu, and a fourth added by
Professor De Candolle, containing the plants with bilabiate florets,
which were either not known, or overlooked, by Jussieu. It may perhaps
be necessary to add, that this arrangement forms the basis of the new
one proposed by De Candolle, and that the principal difference consists
in the subdivisions.
TRIBE I.—CICHORACEÆ.
_Florets ligulate. Juice milky, narcotic._
The plants contained in this tribe bear more or less resemblance to the
common Succory (_Cichorium Intybus_). This beautiful plant, which is
found in great abundance wild in many of the sandy and chalky districts
of England, has large bright blue flowers, which when examined will
be found to consist of a number of florets, all of the kind called
ligulate, that is somewhat like a cornet of paper; the upper part being
broad and flat, and serrated at the edge. The pappus in this genus
is very short, and it is scaly rather than feathery. The leaves are
bitter, and when broken give out a milky juice; and the fleshy roots
when roasted are used to adulterate coffee. The Endive is a variety
of this species, or another species of the same genus. The Sowthistle
(_Sonchus oleraceus_) abounds in the same milky juice as the succory,
and has the same kind of fleshy root. The flower is composed of a
scaly involucre (shown at _a_ in _fig._ 43) and a number of ligulate
florets (see _b_), which when they fall show the pappus (_c_), forming
a feathery ball. The manner in which the pappus is attached to the
seed-vessel is shown at (_d_); and the receptacle after the florets
have been pulled out, but with the involucre still attached to it, at
(_e_). A detached floret is shown at (_f_). The Dandelion (_Leontodon
Taraxacum_) differs from the Sowthistle: in its florets, which are
flatter and looser; in its receptacle, which is globular; and above
all, in its pappus, which is what is called stipitate or stalked, that
is, the tubular part of its calyx rises to a considerable height above
the capsule, before it becomes divided into its feathery segments,
as shown in _fig._ 44. The leaves of this plant are what is called
runcinate, that is, the lobes into which they are cut point downwards
towards the root instead of upwards from it, and the root is also
fleshy. The Lettuce, Salsafy or Goat’s-beard, Ox-tongue, Hawkweed,
Cat’s-ear, Nipplewort or Swine’s Succory, and many other well-known
plants, belong to this tribe.
[Illustration: FIG. 43.—SOWTHISTLE. (_Sonchus oleraceus._)]
[Illustration: FIG. 44.—SEED OF THE DANDELION.]
TRIBE II.—CYNAROCEPHALÆ.
_Florets tubular. Juice watery, tonic._
[Illustration: FIG. 45.—PART OF THE FLOWER-HEAD OF THE BURDOCK.]
The plants in this division all bear more or less relation to the
common Artichoke (_Cynara Scolymus_). The scales of the involucre
are generally fleshy at the base, but terminate outwardly in a sharp
hard point. The florets are tubular, and intermixed with them in the
receptacle are frequently found the hardened bracts, which in this
state are called paleæ, and which appear to be of a chaffy substance,
as exemplified in the choke of the Artichoke, the fleshy receptacle
being in this plant what we call the Artichoke bottom. This peculiar
formation is shown more in detail in _fig._ 45, which represents part
of the flower of the common Bur or Burdock (_Arctium Lappa_), so
annoying from the strong hold it takes of any part of the dress which
it may chance to touch. In _fig._ 45 _a_ is the involucre, every scale
in which is hooked and turned inwards, so as to hold firmly whatever
it may catch; _b_ is a floret showing its tubular shape, and its style
proceeding through the united anthers; _c_ shows the hardened bracts
or paleæ, the other florets having been removed; and _d_ shows a fruit
with a palea attached, magnified. All the different kinds of thistle
belong to this division; and though many of the kinds have not the
hardened bracts, they have all a spiny involucre. The pappus of the
thistle is generally attached to a kind of disk, from which it becomes
loosened soon after the seed falls, and this thistle, down, as it is
called, being extremely light, is blown about by the winds. All the
thistles have fleshy roots, and take firm hold of the soil. The Corn
Blue-bottles (_Centaurea_), the Wild Saffron (_Carthamus tinctoria_),
and many other well-known plants, belong to this division.
TRIBE III.—CORYMBIFERÆ.
_Florets partly tubular and partly ligulate; juice watery; sometimes
bitter and tonic, and sometimes acrid. The seeds of some of the
species yield oil._
The plants included in this tribe all bear more or less resemblance to
the common Daisy. In this well-known flower, the white florets are all
ligulate, and compose what is called the ray, and the yellow flowers,
which are tubular, are called the disk. The involucre is simple and
leafy, and the receptacle is conical. The seeds are without pappus. The
Chrysanthemum is nearly allied to the Daisy, and its seeds also are
destitute of pappus; but it is easily distinguished by its involucre,
which is scaly, and by the flower forming a kind of depressed globe in
the bud. The scales of the involucre are strongly marked, from being
edged with a thin membrane, and the florets of the ray are much longer
in proportion to those of the disk than in the Daisy. The great Ox-eye
Daisy, which was formerly called _Chrysanthemum leucanthemum_, is now
placed in a new genus, and called _Leucanthemum vulgare_; and the
Chinese Chrysanthemums have been removed to the genus _Pyrethrum_. Both
plants, however, will no doubt long continue to be called by their old
names. The beautiful yellow-flowered plant often found growing among
corn (_Chrysanthemum segetum_), the three-coloured Chrysanthemum (_C.
tricolor_ or _carinatum_), and the yellow annual Chrysanthemum (_C.
coronarium_), with some others, have been left by Professor De Candolle
in their old genus. In the Feverfew (_Pyrethrum_), the receptacle
is elevated, and the fruit is crowned with a narrow membrane. The
Pellitory of Spain was formerly considered to belong to this genus,
and afterwards to the Chamomile, but it is now called _Anacyclus
Pyrethrum_. _Matricaria Chamomilla_, the wild Chamomile, has also no
pappus; and in this plant the receptacle is almost cylindrical. The
true Chamomile (_Anthemis nobilis_) greatly resembles the Chrysanthemum
in its flowers; but they are distinguished by having a chaffy
receptacle, and the fruit having a membranous margin. The smell of
the Chamomile is aromatic, and its qualities highly tonic. The Yarrow
(_Achillea millefolium_) is another plant destitute of pappus, but with
a chaffy receptacle; it is also remarkable for its leaves, which are
doubly pinnatifid.
It will be seen by the above enumeration, that in many plants belonging
to this division, the pappus is entirely wanting, and in others it
will be found to assume a different form to that which it bears in
the other tribes. Thus, in the Bur-Marigold (_Bidens_), the pappus
consists of from two to five erect awns, which are covered with very
small, bent bristles. The genus Senecio has soft, hairy pappus, as may
be seen in the common Groundsel (_S. vulgaris_); the leaves of this
weed are pinnatifid, and somewhat stem-clasping, and the flowers have
no ray florets. In other species of this division, however, the ray
florets are very conspicuous: as, for example, in the common yellow
Ragwort (_S. Jacobæa_), in the great fen Ragwort, or Bird’s tongue (_S.
paludosa_), and in the purple Jacobæa (_S. elegans_). Nearly allied
to Senecio, is the genus Cineraria, so much, indeed, that Professor
De Candolle, in his late arrangement of the Compositæ, has included
the greater part of the species in Senecio. The greenhouse species,
with purple flowers, are among those which have been changed; but
they will probably always retain the appellation of Cineraria, as an
arbitrary English name. The Asters, or Michaelmas Daisies, Golden
Rod, Elecampane, Leopard’s Bane, the Cape Marigold, (now called
Dimorphortheca, instead of being included in the genus Calendula),
Coltsfoot, Wormwood, Southern-wood, Tansy, and many other well-known
plants, belong to this division.
The Sunflower (_Helianthemum annuus_) is an example of one of the
plants belonging to this division which has seeds yielding oil. In this
plant the pappus is awl-shaped, and deciduous; and the receptacle,
which is broad and somewhat convex, is paleaceous. The seeds are large
and oblong, and when pressed, yield a considerable quantity of oil. The
Madia is another oil plant; and indeed the seeds of several in this
division yield oil.
TRIBE IV.—LABIATÆFLORÆ.
_Florets bilabiate._
The plants belonging to this division are rarely seen in British
gardens; but when they do occur, they are well worth examining, from
the singularity of their formation. _Mutisialatifolia_ (see fig. 46)
has a large, woolly involucre, the scales of which are of two kinds,
the outer ones, (_a_), being pointed and leaf-like, and the inner ones,
(_b_), having the appearance of scaly bracts. The florets of the ray,
(_c_), are narrow, and spreading in the fully expanded flower; and
those of the disk, (_d_), are shorter, erect, divided into two lips,
which curl back, and the lower one of which is again divided into two
segments (as shown at _e_ in the detached floret). The leaves of this
plant are very curious; the midrib is lengthened and drawn out into a
tendril, as shown at _f_, and the petiole (_g_) is decurrent. There
are several other genera belonging to this tribe, but none of them are
particularly ornamental except _Triptilion spinosum_, which has flowers
of the most brilliant blue, that do not lose the intensity of their
colour in drying.
[Illustration: FIG. 46.—FLOWER AND LEAF OF MUTISIA LATIFOLIA.]