Manihot walkerae
Manihot angustiloba
Texas tapioca, Walker's manihot
desert-mountain manihot, narrow-leaf cassava, pata de gallo
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 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.
stipules lanceolate, entire;
petiole 3–12 cm;
blade basally attached, 5–7-lobed, lobes with acute secondary lobes proximally, median lobe 5–15 cm, margins neither thickened nor revolute, remotely serrate, apex acute, surfaces glabrous, abaxial smooth.
axillary, subspicate racemes, 5–10 cm.
axillary, racemes, to 12 cm.
staminate 1–3 mm;
pistillate 15 mm in fruit, downcurved.
staminate 3–8 mm;
pistillate 10–25 mm in fruit, downcurved.
calyx tubular, base gibbous, midsection constricted, 10–20 mm, lobes erect or spreading;
stamens 6–8.
calyx campanulate, 10–18 mm, lobes erect or spreading;
stamens 10.
1 cm, verrucose-rugose, not winged.
1.5 cm, finely tuberculate, not winged.
globose, 8–9 mm.
globose, 12 mm.
Manihot walkerae
Manihot angustiloba
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.)
D. J. Rogers and S. G. Appan (1973) noted the overall similarity and nearly identical geographic ranges of Manihot angustiloba and M. davisiae, yet they maintained these taxa as separate species, presumably because of their (nearly) constant and consistent differences in leaf lobe outline. Manihot angustiloba has generally narrow, nearly linear, primary lobes with a pair of serrate secondary lobes forming the widest portion of the lobe proximal to the middle; M. davisiae has generally broader leaf lobes with one pair of rounded secondary lobes that form the widest portion of the lobe distal to the middle, or two pairs of nearly equal, rounded, secondary lobes proximal and distal to the middle. Some specimens exhibit an intermediate condition: primary lobes that are narrow distally but also bear a pair of rounded secondary lobes proximal to the middle.
In the flora area, Manihot angustiloba is restricted to Cochise, Pima, and Santa Cruz counties.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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