Smithsonian Contr. Knowl. 5(6): 29, plate 12, fig. B. 1853.
Shrubs, forming relatively tall mounds or upright, 25–300 cm. Stems: branchlets ascending to divaricate, green to grayish green or yellowish green during at least 1st year, soon or tardily turning yellowish brown to orangish brown, slender to relatively stout, 0.5–2 mm diam.; bark of older branches dark gray; tips mostly strongly spinescent (except on new growth); usually glabrous, sometimes puberulent (especially near nodes). Leaves: stipules absent (var. spinescens) or triangular to subulate, fused basal portion usually thickened, darkened, glandular, free tips 0.2–1 mm; blade usually narrowly to broadly oblanceolate, sometimes narrowly elliptic, 3–17 × 1.2–6 mm, margins usually not, sometimes slightly and evenly, thickened, apex acute, sometimes minutely mucronate, mucro 0.1–0.4 mm, usually glabrous, sometimes sparsely to moderately puberulent. Inflorescences axillary, usually flowers solitary, rarely 2–3-flowered. Flowers: sepals 4–5(–6), narrowly ovate to ovate, 1–3 mm, equal or slightly unequal, tips not spinescent; petals 4–5(–6), narrowly elliptic-oblanceolate to oblanceolate, 4–9 × 0.4–1.5 mm; stamens 5–10, in 1 equal or 2 unequal series, longer opposite sepals. Follicles 1 or 2, ovoid to broadly ovoid or broadly ellipsoid, 3–5 mm, moderately to strongly striate, glabrous.
Ariz., Calif., Colo., Idaho, Mont., N.Mex., Nev., Okla., Oreg., Tex., Utah, Wash., Wyo., Mexico.
Varieties 6 (5 in the flora).
Glossopetalon spinescens is here treated as a widespread complex of intergrading varieties showing some geographic localization. This follows N. H. Holmgren (1988, 1997) and differs from M. R. Ensign (1942) and H. St. John (1942), who had fewer specimens available for study. The sixth infraspecific taxon, var. mexicanum (Ensign) H. St. John, is known only from limestone and gypsum outcrops in the mountains of Coahuila and Nuevo León, Mexico. Variety mexicanum is a small-leaved variant similar to var. microphyllum; it differs from that taxon in lacking stipules. Isolated disjunct occurrences of the species in more southern portions of Mexico (Guanajuato, Oaxaca, Tlaxcala, Veracruz) have not been studied.
|1||Stipules absent.||Glossopetalon spinescens var. spinescens|
|1||Stipules present (sometimes not observable when leaves are fasciculate on short shoots)||> 2|
|2||Largest leaf blades 3–7(–8) mm; branchlets usually turning from grayish green to dull orangish brown toward end of 1st year, sometimes later.||Glossopetalon spinescens var. microphyllum|
|2||Largest leaf blades 6–17 mm; branchlets usually turning from grayish green to yellowish brown toward end of 2d or 3d year (sometimes earlier in var. meionandrum)||> 3|
|3||Stipule free portion relatively well developed, mostly narrowly triangular to subulate, 0.5–1.7 mm; leaves often still developing at flowering and early deciduous, branches often appearing nearly leafless during much of growing season.||Glossopetalon spinescens var. aridum|
|3||Stipule free portion relatively poorly developed, usually triangular to narrowly triangular, sometimes subulate, 0.2–0.5(–0.8) mm; leaves mostly well developed at flowering and tardily deciduous, branches appearing leafy during most of growing season||> 4|
|4||Stipule adnate portion yellowish or brownish tinged, often poorly developed, slightly thickened; petals mostly widest near apex, apices rounded or abruptly acute to short-acuminate; stamens 5–7, equal or subequal.||Glossopetalon spinescens var. meionandrum|
|4||Stipule adnate portion dark reddish purple to nearly black, usually well developed, noticeably thickened; petals mostly widest proximal to apex (sometimes nearly oblong), apices rounded to gradually angled or acuminate; stamens usually 8, in 2 unequal series.||Glossopetalon spinescens var. planitierum|