COMMELINALES

the spiderwort order of monocotyledonous flowering plants, comprising four families of mostly tropical and subtropical weak-stemmed herbs. The spiderwort family (Commelinaceae) is the largest and most important of the order. It includes, among its 38 genera and approximately 700 species, the following genera, which provide species grown as garden and indoor ornamentals: the spiderwort (q.v.) genus (Tradescantia, 20 species), including the common spiderwort (T. virginiana) and one of the wandering Jew plants (T. fluminensis); the dayflowers (Commelina, 100 species), of which only 3 are grown ornamentally (C. coelestis, C. diffusa, and C. erecta) for their blue flowers; Dichorisandra (30 species), especially D. mosaica and D. thyrsiflora, both grown as blue-flowered foliage plants; Rectanthera (2 species, formerly Spironema), especially R. fragrans, a fragrant, waxy-white-flowered hanging-basket plant; Moses-in-the-cradle, oyster plant, or boat lily (Rhoeo spathecea, or R. discolor), grown as a potted plant for its purple-coloured leaves and unusual flowers; and Zebrina (q.v.; 2 species), especially the other plant known as the wandering Jew (Z. pendula). The second largest family of the order is the yellow-eyed grass family (Xyridaceae), which has 2 genera (Xyris, 250 species, and Achlyphila, one species). It consists of small, tufted, rushlike marsh plants that mostly grow in the tropics and subtropics of the Americas. Species of Xyris are grown in wild gardens, but otherwise the family is of little economic importance. The family Rapateaceae contains 16 genera and about 80 species of perennial (long-lived) herbs that grow from fleshy rootstocks. These plants, which have leaves with a characteristic 90 lengthwise twist, grow in the dense forests of tropical South America and extreme western tropical Africa. The largest genera are Stegolepis (23 species), Rapatea (20 species), and Saxofriderica (9 species). The smallest of the order is the bogmoss family (Mayacaceae); it has only one genus (Mayaca) with 10 species of freshwater aquatic mosslike herbs. They grow in springs, ponds, and streams in the southeastern United States, Central America, and northern South America. One species of Mayaca is found in tropical Africa.