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_).~