Manihot walkerae
Manihot
Texas tapioca, Walker's manihot
cassava, manioc, yuca
decumbent to ascending (often growing through associated vegetation), 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.
persistent or deciduous, alternate, simple [palmately compound];
stipules present, deciduous;
petiole present [rudimentary], glands absent;
stipels present at apex;
blade usually palmately lobed, rarely unlobed, lobes undivided or secondarily lobed, margins entire, repand, or serrate, laminar glands absent;
venation palmate (pinnate in lobes).
axillary, subspicate racemes, 5–10 cm.
bisexual (pistillate flowers proximal, staminate distal), terminal or axillary, racemes or panicles;
glands subtending each bract 0.
staminate 1–3 mm;
pistillate 15 mm in fruit, downcurved.
present, pistillate often elongating in fruit.
calyx tubular, base gibbous, midsection constricted, 10–20 mm, lobes erect or spreading;
stamens 6–8.
sepals 5, petaloid, 7–20 mm, valvate, connate 1/2 length;
petals 0;
nectary intrastaminal, cushion-shaped, lobed;
stamens (6–8)–10, in 2 whorls, distinct;
pistillode absent.
sepals 5, petaloid, distinct;
petals 0;
nectary annular, lobed or unlobed;
pistil 3-carpellate;
styles 3, connate basally, unbranched, flabellate, prominently papillate.
capsules.
1 cm, verrucose-rugose, not winged.
globose, 8–9 mm.
globose to oblong;
caruncle present.
= 9.
Manihot walkerae
Manihot
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.)
Species ca. 100 (6 in the flora).
Manihot is one of the most economically important members of Euphorbiaceae, primarily because of the starchy food-bearing roots of M. esculenta, now cultivated throughout the tropics. Also, M. glaziovii Müller Arg., from northeastern Brazil, was once an important source of Ceará rubber. Manihot appears to be most closely related to Cnidoscolus, a conclusion supported by morphological (G. L. Webster 1994) and DNA sequence data (K. Wurdack et al. 2005). Four species of sect. Parvibracteatae, as defined by D. J. Rogers and S. G. Appan (1973), barely extend across the borders of Arizona and Texas from Mexico. In addition, two species are naturalized in the southeastern United States.
Leaf blade lobe characters (length, outline) are best developed in the median and immediately adjacent lobes; lateral lobes are progressively smaller and tend to have simpler outlines with distance from the median lobe.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Shrubs or trees; inflorescences panicles; Gulf and Atlantic coastal plains. | → 2 |
2. Leaf blade lobes without secondary lobes; stipules lanceolate, entire; stem nodes conspicuously swollen; leaf and stipule scars elevated, especially on older stems; capsules usually winged. | M. esculenta |
2. Median and adjacent leaf blade lobes with secondary lobes, lateral lobes without secondary lobes; stipules linear, remotely serrate; stem nodes not swollen; leaf and stipule scars not elevated; capsules not winged. | M. grahamii |
1. Herbs or subshrubs; inflorescences racemes; Texas and Arizona. | → 3 |
3. Leaf blade secondary lobes acute, proximal; leaf blade margins remotely serrate. | → 4 |
4. Leaf blade margins neither thickened nor revolute; inflorescences axillary; capsules finely tuberculate; s Arizona and adjacent Mexico. | M. angustiloba |
4. Leaf blade margins thickened and revolute; inflorescences terminal; capsules smooth; s Texas and adjacent Mexico. | M. subspicata |
3. Leaf blade secondary lobes rounded, distal or distal and proximal to middle; leaf blade margins entire. | → 5 |
5. Leaf blades basally attached; staminate calyces campanulate; capsules nearly smooth; s Arizona and adjacent Mexico. | M. davisiae |
5. Leaf blades peltate; staminate calyces tubular, midsection constricted; capsules verrucose-rugose; s Texas. | M. walkerae |
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