Manihot walkerae
Manihot esculenta
Texas tapioca, Walker's manihot
bitter cassava, cassava, manioc, tapioca
decumbent to ascending (often growing through associated vegetation), terete when young;
nodes not swollen;
leaf and stipule scars not elevated.
erect, terete when young;
nodes conspicuously swollen;
leaf and stipule scars elevated, especially on older stems.
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.
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.
axillary, subspicate racemes, 5–10 cm.
axillary, panicles, 2–10 cm.
staminate 1–3 mm;
pistillate 15 mm in fruit, downcurved.
staminate 2–4 mm;
pistillate 20 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.
1.5 cm, usually winged.
globose, 8–9 mm.
subglobose to oblong, 12 mm.
= 36.
Manihot walkerae
Manihot esculenta
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.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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