Polygonaceæ

Polygonaceæ, a natural order of plants, mostly herbs, but including a few shrubs. The leaves are alternate, with stipules cohering around the stem, though sometimes reduced to a mere ring. The flowers are not unfrequently unisexual; the fruit generally a nut, often triangular, the seed with farinaceous albumen, which has an economic importance in buckwheat. The genus Polygonum comprises numerous species, of which several are natives of Britain; in North America twenty-five species are found east of the Mississippi. Knot-grass (P. aviculare) is a very common British weed, and is found in cultivated and waste places in all parts of the world from the tropics to the Arctic regions. The stems of P. amphibium, an inhabitant of ponds and watery ditches all over Britain and Europe, central Asia, and North America, have been used as a substitute for sarsaparilla on the continent of Europe. P. hydropiper, often called Water Pepper, a plant common by sides of lakes and ditches in Britain and North America, is acrid enough to be used as a vesicant. Several species are occasionally used for dyeing, as the Spotted Persicaria (P. persicaria), a very common weed on dunghills and in waste places in Britain; but the only species really important on this account is that called Dyer's Buckwheat (P. tinctorium), a native of China, the cultivation of which has been successfully introduced in France and Flanders. It yields a blue dye scarcely inferior to indigo. P. orientale has long been occasionally cultivated in flower-gardens in Britain, and is quite hardy, although a native of the West Indies. The Bistort (q.v.) belongs to the genus. Fagopyrum cymosum, a species of buckwheat abundant on the mountains of the north of India, affords an excellent substitute for spinach. Fagopyrum esculentum, or Polygonum Fagopyrum (Buckwheat), is cultivated for the sake of its fruit, which furnishes a nutritious diet used in the countries of northern Europe. The Garden Sorrel (Rumex acetosa) and some other species of Rumex have a singular combination of properties in their roots and in their leaves. In the former there is greater or less astringency, due to the presence of tannic and gallic acid; the latter are more or less acidulous, owing to their containing oxalic acid. Rhubarb (q.v.) belongs to this natural order; so does the Dock (q.v.). The root of Pterococcus aphylla, a native of the sandy steppes of Siberia, when cut exudes a clear viscid gum similar to Tragacanth (q.v.), which swells in water and forms a mucilage of a brownish-yellow colour; it is eaten by the Kalmucks in times of scarcity. Its fruit, which is acid, is eaten to quench thirst. Triplaris americana and T. Bonplandiana, both natives of South America, are small trees with hollow branches which are the haunts of small venomous ants that shower themselves on the unwary who may attempt to shelter themselves under their shade. Muhlenbeckia adpressa is the Macquarie Harbour Vine of Tasmania, an evergreen climbing or trailing shrub of most rapid growth, sometimes 60 feet in length. It produces racemes of fruit somewhat resembling grapes or currants, the nut being invested with the large and fleshy segments of the calyx. The fruit is sweetish and subacid, and is used for tarts. Coccoloba uvifera is the Seaside Grape (q.v.) of the West Indies. See also CALLIGONUM.