Rhinoceros Cactus

Mature plants of Coryphantha echinus are dimorphic with respect to presence/absence of porrect (inner or abaxial) central spines. Immature plants of most populations lack central spines, except in the southern and western populations where some individuals produce central spines even before sexual maturation. The name C. pectinata (Engelmann) Britton & Rose was used for plants lacking central spines. Coryphantha echinus was recombined as variety of central Mexican C. cornifera (L. D. Benson 1969c); however, they belong to different species groups.

The showy flowers of Coryphantha echinus are among the most ephemeral in the Cactaceae. They are fully expanded at high noon (if in brilliant sunlight) and wilt after only an hour or two. By mid afternoon, when most Chihuahuan Desert cacti are at the peak of anthesis, the flowers of C. echinus are tightly closed.

Plants usually unbranched (branched with age, forming large clumps to 80 cm diam. at low elevation in Brewster County, Texas), usually relatively smooth except for protruding abaxial central spine, stem largely obscured by spines. Roots diffuse or short taproots. Stems spheric (ovoid or conic with age) to cylindric, 3-15(-20) × 3-7.6 cm; tubercles 8-12 × 6-11 mm, firm; areolar glands seasonally conspicuous; parenchyma not mucilaginous; pith ¹/4-¹/3 of lesser stem diam.; medullary vascular system absent. Spines 16-34 per areole, drab whitish, pale yellowish tan, or pale purplish gray, overlying relatively bright yellow to dark yellow-brown inner layers, later gray with dark tips; radial spines 15-25(-29) per areole, 16-24 × 0.2-0.6 mm; subcentral spines (0-)2-3(-4) per areole, erect; central spines (0-)1-4(-11) per areole, larger spines and abaxial central spine porrect, straight or slightly curved downward (rarely strongly recurved), others appressed, abaxial (or only) central spine 11.5-25 × 0.3-0.9 mm, rigid, others slightly longer and thinner. Flowers nearly apical, 25-65 × 25-65 mm; outer tepals entire; inner tepals 20-37 per flower, bright yellow, sometimes proximally reddish, 22-34 × 4.5-12 mm; outer filaments reddish, reddish orange, or yellow; anthers bright yellow-orange; stigma lobes 10-13, whitish or greenish yellow, 3-4 mm. Fruits green, ovoid, 12-28 × 10-19 mm, slimy; floral remnant strongly persistent . Seeds reddish brown, somewhat comma-shaped, 1.7-1.9 mm, smooth, shiny. 2n = 22 (as C. cornifera var. echinus).

Tex.; Mexico (Chihuahua, Coahuila).

Flowering late spring-summer (Apr-Jul); fruiting 2-4 months after flowering.

Degraded grasslands, desert scrub, on and near limestone or igneous hills and benches, with Larrea; 300-1500m.

Mammillaria echinus Engelmann, Proc. Amer. Acad. Arts 3: 267. 1856 (as Mamillaria); Coryphantha cornifera (de Candolle) Lemaire var. echinus (Engelmann) L. D. Benson; C. pectinata (Engelmann) Britton & Rose; M. pectinata Engelmann

Coryphantha echinus is a species of cactus known by the common names of sea urchin cactus, hedgehog Cory cactus or rhinoceros cactus. C. echinus is found in the south and east portion of the Trans-Pecos to Del Rio, Chihuahua, Coahuila and sporadically in the northeast Trans-Pecos. The plant normally occurs in solitary groupings, but sometimes grows as a clump. It produces short-lived yellow flowers that last for a couple of hours between April and July. After flowering, it produces green fruits.

Coryphantha echinus was first collected by Charles Wright in 1849 and was later described as Mammillaria echinus by George Engelmann.