This family is on one side closely allied to the _Urticaceæ_ by its
solitary, _basal_, _vertical_, and _straight_ ovule, and by the conical
ocrea which envelopes the younger leaves in the bud, similar characters
being present in the Urticaceæ. On the other side it is related to
the Curvembryæ. The flowers are small, often _trimerous_, regular and
slightly perigynous (~in _Chloranthaceæ_, if they properly belong to
this family, and _Houttuynia_, more or less epigynous~). Syncarps are
present in some Piperaceæ, but the fruit is generally a single fruit,
one-seeded berry, nut or drupe. The leaves are generally scattered.
Order 1. =Polygonaceæ.= The majority are herbaceous plants with
round, often jointed stems, scattered leaves and _ocrea_, that is a
membranous, tubular, ligular or stipular structure _inside_ the base
of the leaf, which clasps the stem and axillary bud; the edges of the
lamina are rolled backwards in the bud. The flowers are regular, small,
generally ☿, slightly perigynous, with inconspicuous, simple, green or
white perianth of 5–6 free segments; stamens 5–9 (Fig. 354) sometimes
arranged in two series; gynœceum 2–3 carpels, ovary _unilocular_ with
_one basal_, _straight_ (orthotropous) _ovule_, 2–3 _free styles_.
The fruit is a 2–3-angular nut; the embryo, with mealy endosperm,
is straight or curved (Fig. 355 _H_), often unsymmetrical.--~The
inflorescences are compound, and generally branch from the axils of
the bracteoles, so that the last partial-inflorescences become coiled,
uniparous scorpioid cymes; in _Polygonum_ the two bracteoles unite into
a membranous tube; in _Rheum_ and _Rumex_ there is only one bracteole.~
[Illustration: FIG. 354.--_A_ Diagram of _Rheum_; _B_ of _Rumex_;
_C_ of _Polygonum fagopyrum_; _D_ of _P. lapathifolium_. The
ovules are indicated inside the ovaries; bracts and bracteoles
are not shown.]
_Rheum_ (Rhubarb, Fig. 354 _A_) has a 6-leaved, _petaloid_ perianth (Pn
3 + 3) and 9 stamens (A 3^2 + 3). The _3-winged_ nut is _not_ enclosed
by the perianth.
_Rumex_ (Dock, Fig. 354 _B_) has 6 stamens (A 3^2 + 0); the perianth is
6-leaved (Pr 3 + 3), green or red, and the triangular nut is enveloped
by the 3 interior perianth-leaves, which point upwards and continue to
grow after flowering. These perianth-leaves often have warts on their
outer surface. ~The following are monœcious: _R. acetosa_ and _R.
acetosella_.~
_Polygonum_ (Knot-grass, Figs. 354 _C_, _D_; 355). The _petaloid_
perianth is most frequently 5-merous (2/5 spiral); 5–8 stamens. The nut
is triangular (Fig. 354 _C_, 355), or lenticular (Fig. 354 _D_). ~There
are two whorls of stamens, the external with introrse, and the internal
with extrorse anthers. The gynœceum is often bicarpellate (Fig. 354
_D_).~
The flowers may be considered as constructed upon the
monocotyledonous type. _Pterostegia_ has a perfectly
monocotyledonous flower with 5 trimerous whorls. _Rheum_
likewise, but here the external staminal whorl is doubled (Fig.
254 _A_). _Oxyria_ has a dimerous _Rheum_-flower (4-leaved
perianth, 6 stamens, 2 stigmas). _Rumex_ has a _Rheum_-flower
with the suppression of the internal whorl of stamens (Fig.
354 _B_); _Emex_ is a dimerous _Rumex_. _Polygonum_, to which
_Coccoloba_, _Muehlenbeckia_ and others are related, differs
from _Rheum_ chiefly in having one of the leaves, which in the
latter takes part in the formation of the perianth, developed
in this case into a bracteole (so that the perianth is reduced
to five members), and several or all the stamens in the inner
whorl become suppressed.--The perianth in _Coccoloba_ and
_Muehlenbeckia_ is more or less perigynous and becomes fleshy,
enclosing the fruit. _Muehlenbeckia platyclada_ has flat branches
with rudimentary leaves; sometimes branches with normal,
arrow-shaped leaves are found. _Atraphaxis._
[Illustration: FIG. 355.--_Polygonum fagopyrum_: _A_ branch
with flower and fruits (nat. size); _B_ flower; _C_ the same
in longitudinal section; _D_ anterior and posterior view of
stamen; _E_ gynœceum; _F_ fruit (mag.); _G_ fruit in longitudinal
section; _H_ transverse section, showing the curved cotyledons
embedded in the endosperm; _I_ the embryo.]
POLLINATION. _Rumex_ is wind-pollinated, the stigmas are
therefore large and brush-like (indicated in Fig. 354 _B_).
_Rheum_ and _Polygonum_ are insect-pollinated and have therefore
capitate stigmas, etc.; honey-glands are situated at the base
of the stamens (_d_, in Fig. 354 _C_, and _n_ in Fig. 356); a
few small-flowered _Polygonum_ species are self-pollinated;
Buckwheat (_P. fagopyrum_) is dimorphic and has long-styled and
short-styled flowers (Fig. 356). _Pol. bistorta_ is protandrous
and homostyled.
About 750 species, most of which are found in the temperate
regions of the Northern Hemisphere, some reaching as far as the
snow line or into the Arctic regions (_Oxyria_, _Kœnigia_).
Trees and shrubs are found in the Tropics: _Coccoloba_,
_Triplaris_. _Rheum_ is Central Asiatic.--The thick rhizomes of
_R. officinale_ (_Rhubarb_) are _officinal_. The rhizomes of the
ordinarily cultivated species, _R. undulatum_ and _rhaponticum_,
are used in veterinary medicine. The following are cultivated as
culinary plants for the sake of their leaves:--_Rumex acetosa_
(Sorrel), _R. patientia_, _R. scutatus_, and _Rheum undulatum_
(petioles). Several species of _Polygonum_ (_P. hydropiper_ and
others) have a sharp, pungent taste. “Buckwheat” is the mealy
fruit of _Polygonum fagopyrum_ (Central Asia) and is of value as
a farinaceous food. _P. cuspidatum_ (_P. sieboldi_, Japan) is an
ornamental plant.--_Calligonum_ in sandy and stony deserts.
[Illustration: FIG. 356.--Flower of _Polygonum fagopyrum_ in
longitudinal section: 1, long-styled; 2, short-styled; _a_ the
anthers; _st_ the stigmas; _n_ nectary.]
Order 2. =Piperaceæ (Peppers).= Shrubs or herbs, often with nodose,
jointed stem; leaves simple, entire, often with curved veins; stipules
wanting (_Peperomia_) or intrapetiolar and cap-like, often enclosing
the terminal buds (_Piper_). The flowers in the group _Pipereæ_
(_Piper_, Fig. 357, and _Peperomia_) are borne in spikes with fleshy
axes (_club-like_), seldom in racemes, the outer ones are crowded and
are ☿ or unisexual, always small, _naked_ and without bracteoles;
~generally stamens 3 + 3, and gynœceum 3, but the number of the
stamens may be reduced by suppression to 2, and the carpels to 1~. The
flowers are situated in the axils of the small, generally shield-like
floral-leaves. The ovary is always _unilocular_ and has _one upright,
orthotropous_ ovule. Fruit a berry or drupe. Both endosperm and
_perisperm_ are present, the latter being especially well developed
(Fig. 359).
_Piper_; generally shrubs with scattered leaves, and terminal
inflorescences which are crowded to one side by the development of the
highest lateral bud, so that they are situated opposite the leaves
(Fig. 357). Many species have stems with an abnormal anatomical
structure.--_Peperomia_; chiefly succulent herbs, often epiphytes, with
opposite or verticillate leaves having aqueous tissue on the upper side.
[Illustration: FIG. 357.--_Piper nigrum_: branch with fruit (½)]
The group _Saurureæ_ (considered by some as an order, and
perhaps representing a more original type) has 3–4 carpels
with many ovules. _Lactoris_ stands the highest with regular
3-merous perianth, 3 + 3 stamens and 3 carpels, which are
united at the base. Fruit a capsule with several seeds. (It
has one species from the island of Juan Fernandez, and is also
placed in an order of its own, Lactoridaceæ, allied to the
Magnoliaceæ, through _Drimys_).--_Saururus_ has naked flowers;
most frequently 6 stamens, and 4 carpels, free or united at
the base, each with 2-4 orthotropous ovules. Fruit, small
berries.--_Houttuynia_; stamens situated a little upward on the
ovaries; placentation parietal; capsule many-seeded.
About 1,000 species; entirely tropical, especially from
South America and East India. They are found chiefly among
the underwood in damp, shady places; some, which are fleshy
(_Peperomia_), live as epiphytes on trees; a few climb by
roots.--USES. Several Piperaceæ are used medicinally and
for spices on account of their pungent properties and the
essential oils found in nearly all parts of the plant. The
following are _officinal_: “Black-pepper” (the unripe, dried
fruits) and “White-pepper” (the seeds of the ripe fruits) of
_Piper nigrum_ (climbing shrub, East Indian); “Cubeb” berries
of _P. cubeba_ (climbing shrub, Java). “Long-pepper” is the
unripe inflorescence of _P. longum_, East India. The leaves of
_P. angustifolia_ (Matico) are officinal. The leaves of the
Betelpepper (East India) are used together with the nuts of
the Areca-palm to form the well-known East Indian intoxicating
compound “Betel.” A good many others are also used.
[Illustration: FIG. 358.--_Piper nigrum_ (Diagram). In addition
to the bract there are two structures resembling bracteoles.]
[Illustration: FIG. 359.--_Piper nigrum_: Fruit in longitudinal
section, showing the endosperm, perisperm, and pericarp.]
Order 3. =Chloranthaceæ.= (_Chloranthus_, _Hedyosmum_) have
opposite leaves, with stipules more or less united at the base,
and inferior “drupes.” Ovules pendulous. Only endosperm. About
33 species, Tropical.