Plains greasebush

Forsellesia planitierum Ensign, Amer. Midl. Naturalist 27: 509, fig. 8. 1942; Glossopetalon planitierum (Ensign) H. St. John

Shrubs, 40–120 cm. Branchlets usually ascending, usually turning from grayish green to yellowish brown toward end of 2d or 3d year, glabrous or nearly so. Leaves mostly well developed at flowering and tardily deciduous, branches appearing leafy during most of growing season; stipules present, sometimes difficult to observe, adnate portion dark reddish purple to nearly black, usually well developed, noticeably thickened, free portion relatively poorly developed, triangular to narrowly triangular or subulate, 0.2–0.4 mm; largest blade 6–14 × 2–4 mm, margins ciliolate, moderately puberulent, sometimes glabrescent. Petals 4–6 mm, mostly widest proximal to apex ˂sometimes nearly oblong˃, apex rounded to gradually angled or acuminate, tips blunt or sharply pointed. Stamens usually 8 in 2 unequal series.

Flowering Mar–May. Upland prairie slopes, crevices, ledges, cliff tops, drainages, outcrops, on limestone, gypsum, and sandstone substrates; 800–1600 m; Colo., N.Mex., Okla., Tex.

The range of var. planitierum is centered on the Texas Panhandle; it does not overlap with those of other members of the Glossopetalon spinescens complex. M. R. Ensign (1942) noted an unusual collection from near the Louisiana border in Marion County, Texas (Harris 470, US). This disjunct occurrence, upon which Ensign equivocated, would extend the distribution of the taxon significantly eastward and significantly lower its elevational limit (and that of the entire genus) to about 50 m. Plants have not been rediscovered in eastern Texas since 1930.