4. Manihot grahamii Hooker, Icon. Pl. 6: plate 530. 1843. (as grahami).
Hardy tapioca, Graham's manihot or cassava Hardy tapioca, Graham's manihot or cassava
Shrubs or trees, 2–6[–7] m. Roots not thickened. Stems erect, angled when young; nodes not swollen; leaf and stipule scars not elevated. Leaves deciduous; stipules linear, remotely serrate; petiole 5–33 cm; blade basally attached, 5–13-lobed, median and adjacent lobes with pair of weakly defined rounded secondary lobes distal to middle, lateral lobes without secondary lobes, median lobe 5–24 cm, margins neither thickened nor revolute, entire, apex acuminate, surface glabrous, abaxial smooth. Inflorescences axillary, panicles, to 30 cm. Pedicels: staminate 4–10 mm; pistillate 10–40 mm in fruit, straight. Staminate flowers: calyx campanulate, 10–15 mm, lobes erect or spreading; stamens 10. Capsules 1.8 cm, smooth, not winged. Seeds oblong, 10–12 mm.
Flowering Apr–Aug; fruiting Jun–Sep. Disturbed areas, spreading from cultivation; 0–600 m; introduced; Ala., Ark., Fla., Ga., La., Miss., Tex.; South America.
Manihot grahamii is native to northern Argentina, southeastern Brazil, Paraguay, and Uruguay, and is sometimes cultivated for its distinctive, attractive foliage. The flowers are relatively inconspicuous, but are much-visited by bees. This is the most cold-tolerant Manihot species; above-ground stems survive light frosts and if severe cold kills the aerial shoot system outright, new stems can regenerate from underground parts. It survives well and self-sows in garden settings as far north as tidewater Virginia; northern limits for the persistence of plants escaping from cultivation have yet to be established. In addition to characteristics noted in the key, herbarium specimens frequently exhibit contracted petiole bases.