Walker's manihot, Texas tapioca Walker's manihot, Texas tapioca

Herbs or subshrubs, to 1.5 m. Roots thickened. Stems decumbent to ascending (often growing through associated vegetation), terete when young; nodes not swollen; leaf and stipule scars not elevated. Leaves: 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. Inflorescences axillary, subspicate racemes, 5–10 cm. Pedicels: staminate 1–3 mm; pistillate 15 mm in fruit, downcurved. Staminate flowers: calyx tubular, base gibbous, midsection constricted, 10–20 mm, lobes erect or spreading; stamens 6–8. Capsules 1 cm, verrucose-rugose, not winged. Seeds globose, 8–9 mm.

Flowering Apr–Sep, following rains. Shrublands and grasslands; of conservation concern; 20–200 m; Tex.; Mexico (Tamaulipas).

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.