Flora of North America species comparison

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Echinocactus horizonthalonius

biznaga-tonelmancamula, blue barrel cactus, devilshead, silverbell cactus, Turk's head cactus, visnaga meloncillo
Habit Plants normally unbranched.
Stems

pale gray-green to bright gray-blue, flat-topped or hemispheric and deep-seated in sub-strate, spheric with age or stoutly short cylindric (remaining hemispheric at high elevations), 4–25(–45) × 8–15(–20) cm;

ribs (7–)8(–9), vertical to helically curving around stem, rib crests broadly rounded, uninterrupted or slightly constricted between areoles.
Spines

(5–)8(–10) per areole, loosely projecting or strongly decurved, pink, gray, tan, or brown, strongly annulate-ridged, subulate, ± flattened, glabrous, generally not hiding stem surface;

radial spines 5(–8) per areole, similar to central spines;

central spines 1(–3) per areole, 18–43 × 1–2.5(–3) mm, longest spine usually descending, straight or decurved throughout its length.
Flowers

5–7 × 5–6.5(–9.5) cm;

inner tepals bright rose-pink or magenta, color ± uniform from base to apex, 3 × 1.5 cm, margins entire to serrate;

stigma lobes pinkish to olive.
Fruits

indehiscent or weakly dehiscent through basal abscission pore, pink or red, spheric to ovoid-cylindric, surfaces partly or entirely hidden by hairs from axils of scales and long areolar hairs of stem apex, usually quickly drying to tan shell before seed dispersal, 10–30 mm;

scales several, tips dark, spinelike, glabrous.
Seeds

black or gray, angular or slightly wrinkled, spheric to obovoid, 2–3 mm;

testa cell surfaces slightly convex, with weak network pattern of slightly protruding anticlinal cell walls.
2n

= 22.

Echinocactus horizonthalonius
Phenology Flowering Apr–Sep.
Habitat Arid rocky slopes, primarily limestone
Elevation 600-1700(-2500) m (2000-5600(-8200) ft)
Distribution
from FNA
AZ; NM; TX; Mexico
[WildflowerSearch map]
[BONAP county map]
Discussion

The Sonoran Desert populations of Echinocactus horizonthalonius have been segregated as var. nicholii, but are relatively similar to plants in New Mexico and extreme western Texas. Much greater morphologic diversity exists farther east and in Mexico, where shorter-spined, nearly flat-topped plants, which are more distinctive than the Sonoran Desert populations, have escaped taxonomic distinction.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 4, p. 189.
Parent taxa Cactaceae > subfam. Cactoideae > Echinocactus
Sibling taxa
E. polycephalus, E. texensis
Synonyms E. horizonthalonius var. nicholii
Name authority Lemaire: Cact. Gen. Sp. Nov., 19. (1839)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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