2. Dimorphocarpa membranacea (Payson) Rollins, Publ. Bussey Inst. Harvard Univ. 30. 1979; Dithyrea membranacea Payson, Ann. Missouri Bot. Gard. 5: 149. 1918. TYPE: Mexico, Tamaulipas, vicinity of Victoria, 1 Feb–9 Apr 1907, Edward J. Palmer 87 (holotype, MO!; isotypes, GH!, NY!, US!).
Herbs, perennial. Stems to 5 dm, decumbent, branched at base and above. Basal leaves petiolate; leaf blade broadly lanceolate, sinuate-dentate to subentire; upper cualine leaves short-petiolate, ovate to suborbicular, 1–4 x 0.5–3 cm, base abruptly narrowed to petiole, margin dentate. Fruiting pedicels spreading, 1–1.5 cm. Sepals narrowly oblong, 3–4 x 1–1.3 mm, reflexed; petals white, obovate to broadly spatulate, 4–5 mm; claw ca. 1.5 mm, expanded at base. Fruit halves orbicular, 3–4 x 3–4 mm, rounded at apex and base, not margined, pubescent with two sizes of trichomes; style 0.5–1 mm. Seeds broadly oblong, flattened, ca. 2.5 x 2 mm.
Flowering: Aug–Feb.
Habitat: Shrubby areas.
Distribution: Mexico (San Luis Postos Tamaulipas).