POLYGALALES

the milkwort order of dicotyledonous flowering plants comprising five families, with 26 genera of herbs, shrubs, small trees, and vines. They are characterized by the presence in most species of simple leaves and bilaterally symmetrical, bisexual flowers of distinctive structure that superficially resemble those of the pea family (Fabaceae). Despite this resemblance, the order is related instead to the geranium order (Geraniales), which is considered to be its evolutionary ancestor. The milkwort family (Polygalaceae), with 12 genera and about 1,000 species, is the largest, most typical, and most important of the order; its members are found throughout the world except in New Zealand, Polynesia, and the far northern parts of North America and Asia. The chief genera are Polygala (500 to 600 species, mostly herbs, with the distribution of the family), Monnina (150 species, Mexico to Chile), Muraltia (115 species, South Africa), Securidaca (80 species, vines and climbers of the tropics excepting Australia), and Xanthophyllum (60 species, trees of the Indo-Malayan region that accumulate aluminum in their leaves). The genus Salomonia (8 species, Indo-Malayan region and Australia) contains saprophytic (deriving nutrients from decaying matter) plants with scalelike leaves. The seeds of many milkworts (Polygala species) have a fleshy appendage (aril) that attracts ants, which carry the seeds about for food and thus distribute them. The milkwort family is important for the Seneca snakeroot (the root of Polygala senega), which is used medicinally. The only genus with any horticultural importance is Polygala, with about two dozen species grown as ornamentals-e.g., the bastard box (P. chamaebuxus), used in rock gardens; the orange milkwort (P. lutea), with showy yellow flowers and used in bog gardens; and the flowering wintergreen or fringed milkwort (P. paucifolia), which has purple flowers and is grown in wildflower gardens. All are small herbs less than 30 centimetres (one foot) tall. The common milkwort (P. vulgaris) produces showy white, pink, or bluish flowers, usually on separate plants but sometimes on the same plant. The family Vochysiaceae, mostly consisting of trees and shrubs of Central America and tropical South America, contains six genera and 200 species, of which the most important are Vochysia (105 species), Qualea (60 species), Erisma (20 species), and Callisthene (10 species). The family Trigoniaceae, with four genera and 35 species, consists mostly of shrubs and climbers of Central America and tropical South America. The genera are Trigonia (30 species), and Lightia, Trigoniastrum, and Humbertiodendron, which have only one or two species each. The family Tremandraceae is a group of small herbs and heather-like shrubs of Australia that have small leaves. Unlike the other families of the order, which have irregular (bilaterally symmetrical) flowers, those of this family are regular (radially symmetrical). The genera are Tetratheca (20 species), Tremandra (2 species), and Platytheca (one species). The family Krameriaceae (of doubtful inclusion) comprises the genus Krameria, 15 species of shrubs that occur in warm regions from the southern United States to Chile. They are little-known parasites on the roots of other plants.