Stems 3–38 × (2–)4–10(–18) cm; ribs 8–13 (plant often reaching sexual maturity while still entirely tuberculate); areoles spaced 6–20 mm apart along ribs. Spines (8–)12–30 per areole; radial spines (8–)12–20(–27) per areole, straw colored or white, contrasting with all other spines, 9–35(–45) × 0.3–1 mm, adaxial 1–3+ spines of areole strongly flattened, bladelike or ribbonlike, to 4 times wider than thick, 16–75(–100) mm (usually absent from sexually immature plants); central spines (9–)13–42(–58) × (0.2–)0.4–1.5 mm. Flowers: inner tepals rose-pink to magenta, marked with scarlet or orange proximally, sometimes with white band or margins near bases; stigma lobes reddish to red-orange or pale reddish brown or yellowish. Seeds finely papillate with strongly convex testa cells. 2n = 22.

Distribution

• Generated Map
• Legacy Map

Tex., Mexico.

Discussion

Varieties ca. 4 (2 in the flora).

Thelocactus bicolor varies geographically, and an indefinite number of segregate taxa may deserve recognition in Mexico.

Selected References

None.

Lower Taxa

Thelocactus bicolor var. bicolor, Thelocactus bicolor var. flavidispinus

Key

1	Areoles and spines larger; spines red and white, (older spines weather to ashy white), yellow color-form absent; widespread in s Texas and Big Bend region	Thelocactus bicolor var. bicolor
1	Areoles and spines smaller; spines usually yellow (rarely red, 0-5% in all populations); only in Marathon Basin of n Brewster County, Texas	Thelocactus bicolor var. flavidispinus