Shrubs, 1–4 m. Roots thickened. Stems erect, terete when young; nodes conspicuously swollen; leaf and stipule scars elevated, especially on older stems. Leaves persistent; stipules lanceolate, entire; petiole 3–20 cm; blade basally attached, usually 3–10-lobed, sometimes unlobed, lobes without secondary lobes, median lobe 5–18 cm, margins neither thickened nor revolute, entire to ± repand, apex acuminate, surfaces glabrous or hairy, abaxial finely reticulate. Inflorescences axillary, panicles, 2–10 cm. Pedicels: staminate 2–4 mm; pistillate 20 mm in fruit, straight. Staminate flowers: calyx campanulate, 10–15 mm, lobes erect or spreading; stamens 10. Capsules 1.5 cm, usually winged. Seeds subglobose to oblong, 12 mm. 2n = 36.

Flowering year-round, mostly fall and winter. Disturbed areas, spreading from cultivation; 0–200 m; introduced; Ala., Fla., Tex.; South America (Brazil); introduced widely in tropical and subtropical regions worldwide.

The enlarged storage roots of Manihot esculenta yield a starchy staple, now much consumed in tropical regions around the world. Tapioca, a pelletized and partially hydrolyzed form of cassava starch, is the chief form of consumption in temperate regions. Multiple cultivars are known. These are generally characterized as bitter (containing cyanogenic glycosides, which must be removed before consumption) or sweet (cyanogenic glycosides absent or at low levels). A form with variegated leaves is sometimes grown for ornament. Cassava was cultivated throughout the Neotropics in pre-Columbian times. As a root crop with poor storage qualities adapted to humid regions, archeological remains are few, leading to much speculation in the literature about the origin of this important crop. Molecular data reported by K. Olsen and B. A. Schaal (1999, 2001), indicate that cultivated cassava constitutes M. esculenta subsp. esculenta, derived by artificial selection from its sole wild ancestor, M. esculenta subsp. flabellifolia (Pohl) Ciferri from the southern border of the Amazon basin. Under this classification, all North American plants belong to subsp. esculenta.

SELECTED REFERENCES Allem, A. C. 1994. The origin of Manihot esculenta Crantz (Euphorbiaceae). Genet. Resources Crop Evol. 41: 133–150. Olsen, K. and B. A. Schaal. 1999. Evidence on the origin of cassava: Phylogeography of Manihot esculenta. Proc. Natl. Acad. Sci. U.S.A. 96: 5586–5591. Olsen, K. and B. A. Schaal. 2001. Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) and its wild relatives: Further evidence for a southern Amazonian origin of domestication. Amer. J. Bot. 88: 131–142. Rogers, D. J. 1965. Some botanical and ethnological considerations of Manihot esculenta. Econ. Bot. 19: 369–377.