Order XXXVIII. Polygonaceae, Lindl.—Buckwheats.
Characters.—Calyx free, often coloured, imbricated in aestivation. Stamens very rarely perigynous, usually definite and inserted in the bottom of the calyx, anthers dehiscing lengthwise. Ovary free, usually formed by the adhesion of 3 carpels, 1-celled, with a single erect ovule, whose foramen points upwards; styles and stigmas as many as the carpels. Ovules othotropal. Nut usually triangular, naked, or protected by the calyx. Seed with farinaceous albumen, rarely with scarcely any; embryo inverted, generally on one side, sometimes in the axisradicle superior, long.—Herbaceous plants, rarely shrubs. Leaves alternate, their stipules cohering round the stem in the form of an ochrea (or boot); when young rolled backwards, occasionally wanting. Flowers occasionally unisexual, often in racemes (Lindley).
Properties.—The herbaceous plants are distinguished by their acidulous character. They owe this to the presence of vegetable acids, chiefly oxalic acid. This is found in the form of a superoxalate of potash (or soda), which communicates to the leaves and petioles refreshing and refrigerant qualities. The roots contain colouring and astringent matter, and often oxalate of lime. Some of them are purgative. The seeds of some species serve as a kind of corn for cattle, and, in times of scarcity, for man.