Manihot walkerae
Manihot grahamii
Texas tapioca, Walker's manihot
Graham's manihot, Graham's manihot or cassava, hardy tapioca
decumbent to ascending (often growing through associated vegetation), terete when young;
nodes not swollen;
leaf and stipule scars not elevated.
erect, angled when young;
nodes not swollen;
leaf and stipule scars not elevated.
stipules lanceolate, entire;
petiole 1–7 cm;
blade peltate, 3–5-lobed, lobes with rounded secondary lobes distal to middle or with 2 pairs of rounded secondary lobes of nearly equal width proximal and distal to middle, median lobe 2–7 cm, margins neither thickened nor revolute, entire, apex cuspidate, surfaces glabrous, abaxial smooth.
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.
axillary, subspicate racemes, 5–10 cm.
axillary, panicles, to 30 cm.
staminate 1–3 mm;
pistillate 15 mm in fruit, downcurved.
staminate 4–10 mm;
pistillate 10–40 mm in fruit, straight.
calyx tubular, base gibbous, midsection constricted, 10–20 mm, lobes erect or spreading;
stamens 6–8.
calyx campanulate, 10–15 mm, lobes erect or spreading;
stamens 10.
1 cm, verrucose-rugose, not winged.
1.8 cm, smooth, not winged.
globose, 8–9 mm.
oblong, 10–12 mm.
Manihot walkerae
Manihot grahamii
Manihot walkerae is a globally endangered species known from Duval, Hidalgo, and Starr counties and nearby Tamaulipas, Mexico. It is restricted to areas of sandy or gravelly calcareous soils overlying caliche or limestone bedrock. An estimated 95 percent of its habitat in the United States portion of the lower Rio Grande Valley has been converted to largely agricultural uses (www.natureserve.org).
The stamen number (6–8) of Manihot walkerae is notable relative to that of other species in the genus, which typically have 10 stamens per staminate flower.
Manihot walkerae is in the Center for Plant Conservation's National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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