Bull. Torrey Bot. Club 49: 251. 1922.
Plants erect, branched or unbranched, not deep-seated in substrate. Roots diffuse. Stems unsegmented, gray-green to yellowish or bronze-tinted green, spheric to short cylindric, 5–10(–24) × (1.8–)2.5–6.5(–8) cm, usually white woolly at apex; tubercles prominent, not confluent into ribs, tightly packed in vertical, sprialing rows as if tuberculate ribs, compressed conic, 7–12 × 4–7 mm, 8–18 mm diam. at base; areoles adaxially elongated into long, narrow, conspicuous grooves extending into axils of tubercles, usually short woolly; areolar glands absent; cortex and pith not mucilaginous; specialized, yellow, sticky layer beneath old bark. Spines 9–17[–26] per areole, white, gray, brown, or black, acicular, straight; radial spines 9–15[–25] per areole, with bulbous bases, 6–17 mm; central spines [0–]6(–8) per areole, terete with bulbous bases. Flowers diurnal, at stem apex, at axillary end of areolar groove, showy, short funnelform, 2.5–3.2 × 3–5.5 cm; outer tepals whitish or magenta to purplish, to 25 × 10 mm, margins entire (sometimes irregularly, minutely denticulate); inner tepals bright rose-pink or magenta, 15–32 × 5–11 mm, margins entire; ovary smooth, spineless; stigma lobes 4–7, white to cream, 2–4 mm. Fruits dehiscent along vertical slits or indehiscent, green to white (slightly pinkish near base), becoming tan or greenish brown, spheric, 4–10 × 4–8 mm, dry and papery, smooth, spineless; pulp absent; floral remnant deciduous. Seeds black to gray, obovoid or pyriform, 1.1–1.6 × 0.8–1.2 mm, papillate; testa cells strongly convex. x = 11.
Arid regions, sw United States, Mexico.
Species 2 (1 in the flora).
Neolloydia is conspicuous, variable, and often confused with unrelated species, especially in Coryphantha. The papillate seeds are immediately diagnostic for distinguishing Neolloydia species from Coryphantha (seeds pitted, smooth, or ± reticulate), but they are seldom seen.
Several other genera, especially Thelocactus and the Mexican Turbinicarpus, have been variously associated with Neolloydia. Alone among authors, L. D. Benson (1969, 1982) inexplicably submerged Echinomastus into Neolloydia. A long list of differences distinguish Neolloydia from Echinomastus (E. F. Anderson 1986). Chloroplast DNA evidence (C. A. Butterworth et al. 2002) indicated no close relationship between Neolloydia and the surveyed species of Turbinicarpus and Thelocactus; Echinomastus was not represented in the study.