Mamillaria macromeris Engelm. Wisliz. Rep. 13 (1848).
Mamillaria heteromorpha Scheer in Salm. Cact. Hort. Dyck. 128
(1850).
Mamillaria dactylithele Labouret, Monogr. Cact. 146 (1858).
Ovate or cylindrical, 5 to 10 cm. high, simple or branching from
the base and at length cespitose: tubercles large, loose and
spreading, from a dilated base, more or less elongated (12 to 30
mm.) and teretish (often incurved), the groove absent in young
plants and never reaching the axil: radial spines 10 to 17,
slender and terete, or stouter and often angled, spreading, 12 to
40 mm. long, whitish (or more or less rose-colored when young),
straight or a little curved; central spines 4 (or fewer in young
plants or even wanting), spreading, 25 to 55 mm. long, stouter,
bulbous at base, mostly black (the lowest the longest and
stoutest), straight or sometimes curved or twisted: flowers 6 to
7.5 cm. long and of same diameter, deep red to purple: fruit
ovate-subglobose, green, 15 to 25 mm, long: seeds
globose-obovate, yellow, and smooth. 1.2 to 1.6 mm. long. (Ill.
Cact. Mex. Bound. t. 14 and 15) Type, Wislizenus of 1846 in
Herb. Mo. Bot. Gard.
Mostly in loose sand, in the valley of the Rio Grande (on both
sides of the river), from southern New Mexico to Eagle Pass,
Texas, and doubtless further down.
Specimens examined: New Mexico (Wislizenus of 1846; Wright 384,
531, of 1852; G. R. Vasey of 1881): Texas (Wright of 1850, 1851,
1852; Bigelow of 1852): Chihuahua (Evans of 1891; Budd of 1891):
also growing in Mo. Bot. Gard. 1893.
This species shows an interesting transition from Coryphantha to
Echinocactus. The woolly groove of the Coryphantha extends from
the spine-bearing areola to the axil of the tubercle, where it
expands into the flower-bearing areola. In C. macromeris the
groove extends only about half way down the tubercle and gives
origin to the flower-bearing areola on the side of the tubercle;
while in Echinocactus the flower-bearing areola becomes adjacent
to the spine-bearing areola and the flower appears at the summit
of the tubercle.