It is a question whether this variety does not merely represent an older and better developed plant than those upon which the species is based. Mr. Harry I. Budd, who has made extensive collections of Texan and Mexican Cacti for the market, reports that it is impossible to separate sharply the variety from the species in the field, and regards the difference merely as one of age. Unfortunately, only living material of the species could be examined, but its characters seem well sustained even in the most vigorous plants, some of which reach the size of the variety. Through this variety the species is brought very near the following:
14. Cactus bispinus.
Mamillaria microthele Muhlenpf. Allg. Gart. Zeit. p. 11
(1848),
not Lem. (1838).
Differs from the last form (var. greggii) chiefly in its cespitose habit, much larger tubercles, and two unusually stout and short central spines (fide Engelmann, who examined specimens in Coll. Salm-Dyck).
Credited to Mexico in general, but said by Budd to occur within the southern border of Pecos County, Tex.
** Central spines present and one or more hooked.
+ Mostly globose and simple plants (occasionally somewhat
cylindrical).
15. Cactus wrightii (Engelm.) Kuntze. Rev. Gen. Pl. 261 (1891).
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).