Mamillaria wrightii Engelm. Syn. Cact. 262 (1856).
Globose or depressed globose (top-shaped below), 3 to 7.5 cm. in
diameter, simple: tubercles 10 to 12 mm. long, with naked axils:
radial spines 8 to 12, white (the upper dusky-tipped), pubescent,
8 to 12 mm. long central spines mostly 2 (usually side by side
and divergent), rarely 1 or 3, scarcely longer, hooked and
reddish-black: flowers 2.5 cm. long, bright purple: fruit about
2.5 cm. long, somewhat subglobose, purple: seeds 1.4 mm long,
black and pitted. (Ill. Cact. Mex. Bound. t.8. figs. 1-8) Type,
Wright of 1851 in Herb. Mo. Bot. Gard.
High plains and rocky places, from the Upper Pecos, east of Santa
Fe, N. Mex., southward through extreme southwestern Texas
(between the Pecos and El Paso), and into Chihuahua (near Lake
Santa Maria).
Specimens examined: New Mexico (Wright of 1851; Rusby of 1880):
also growing in Mo. Bot. Gard. 1893.
Dr. Engelmann calls attention to the fact that this species is
closely allied to the Mexican C. zephranthoides (Scheidw.), but
in the absence of material representing the latter species no
comparison can be made. In descriptions of the Mexican species
the differently colored flowers and the much longer spines
suggest differences that an examination of fruit and seed
characters may still further emphasize.