Plants erect, commonly unbranched, becoming many branched and moundlike in old age, deep-seated in substrate. Roots taproots. Stems unsegmented, usually gray-green or blue-green to dark green [yellow-green in L. diffusa of Mexico], usually flat-topped and cryptic in soil surface, sometimes protruding above it with recessed apex, ribbed or weakly tuberculate, 2–7.5 × (4–)5–12 cm, softly fleshy, soft skinned, dull, glabrous; ribs 5, 8, or 13 (rarely 21), low, broadly rounded, straight, vertical or less often helically curved around stem; areoles 3–15+ mm apart along ribs or at apices of low, humplike tubercles, circular, copiously hairy, hairs usually in compact, erect tufts to 7–10 mm; areolar glands absent; cortex and pith not mucilaginous. Spines absent. Flowers diurnal, deeply nestled in copious areolar hairs at stem apex, arising from adaxial edges of areoles, campanulate, 1–3 × (1–)1.5–2.5 cm; outer tepals whitish to greenish pink, midrib greenish, margins entire or minutely fringed or ciliate distally; inner tepals usually white to pink [rarely yellowish white or magenta to reddish violet, at least in Coahuila, Mexico], 8–14(–22) × (1–)2.5–5 mm, margins ciliate or entire; ovary smooth, scales, hairs, and spines absent; stigma lobes (3–)4–8, white or pinkish, 1–3 mm. Fruits indehiscent, white to pinkish [to purple], clavate to nearly cylindric, 11–25 × (2–)4–5 mm, weakly succulent, quickly drying and contracting after ripening, upon drying becoming translucent and brownish white or whitish, spines and scales absent; pulp colorless; floral remnant weakly persistent or tardily deciduous. Seeds black, somewhat pyriform, cylindric, or obovoid, 1–1.5 × 1–1.2 mm, not glossy, with large, flat hilum; testa cells strongly convex. x = 11.

Distribution

Arid regions, sw United States, Mexico.

Discussion

Species 2 (1 in the flora).

Selected References

None.

Lower Taxa

Lophophora williamsii