POLYGONALES

the buckwheat order of dicotyledonous flowering plants comprising the family Polygonaceae, with about 40 genera of herbs, shrubs, and trees. The plants are characterized by the presence in most species of leaves that have an appendage (ochrea) that clasps the stem just above the base of the leafstalk. The flowers are radially symmetrical and bisexual and have a single-chambered ovary with one basally positioned ovule. The flowers are variable in the structure and number of their petallike parts and stamens (the male pollen-producing structures). The perianth (petallike parts) consists of three, four, five, or six members that are not differentiated into sepals and petals. The fruits are nearly always small, triangular, one-seeded, nutlike structures with membranous wings formed from the persistent perianth. The seeds are distributed by wind. The largest genera include Polygonum (300 species), Eriogonum and Rumex (200 species each), Coccoloba (150 species), Calligonum (80 species), Chorizanthe (50 species), Rheum (25 species), and Oxygonum (30 species). Some botanists classify the Polygonaceae as a family of the order Caryophyllales. The order is not of great economic importance, though there are some notable species. Buckwheat (Fagopyrum esculentum) is cultivated for its edible seeds and as an animal-feed plant. The leafstalks of rhubarb (Rheum rhaponticum) are edible, but the leaf blades are poisonous. The sea grape (Coccoloba uvifera), growing on beaches, produces edible fruit. Ornamental plants include the sea grape; the sacaline (Polygonum sachalinense); the silver-lace vine (P. aubertii); the fleeceflower (P. reynoutria, or P. cuspidatum compactum), an aggressive ground cover; the ribbonbush, or tapeworm plant (Homocladium platycadum); and the coral vine (Antigonon leptopus). A number of common weeds and pasture plants belong to this order-e.g., the common sorrel, or dock (Rumex acetosa), and sheep's sorrel (R. acetosella).