25. Rheum Linnaeus, Sp. Pl. 1: 371. 1753. Gen. Pl. ed. 5, 174. 1754.
Rhubarb [Greek rheon, a name used by Dioscorides, probably for a plant in this genus]
Craig C. Freeman
Herbs, perennial; roots fleshy. Stems erect, glabrous or pubescent. Leaves deciduous, mostly basal, alternate, petiolate; ocrea persistent or deciduous, chartaceous; blade cordate-ovate to orbiculate or reniform, margins entire, undulate. Inflorescences terminal, paniclelike, pedunculate. Pedicels present. Flowers bisexual, 1-10 per ocreate fascicle, base stipelike; perianth nonaccrescent in fruit, whitish green or pinkish green, campanulate, glabrous; tepals 6, distinct, sepaloid, dimorphic, outer 3 narrower than inner 3; stamens (6-)9; filaments distinct, free, glabrous; anthers yellow or pinkish, elliptic; styles 3, erect or deflexed, distinct; stigmas capitate. Achenes exserted, dark brown, winged, 3-gonous, glabrous. Seeds: embryo straight or curved. x = 11.
Species ca. 60 (1 in the flora): introduced; temperate regions, Eurasia.
SELECTED REFERENCE
Chin, T. C. and H. W. Youngken. 1947. The cytotaxonomy of Rheum. Amer. J. Bot. 34: 401-407.
