Global Range: New Mexico from Sierra and Hidalgo Cos. to DeBaca and Eddy Cos.; just into Arizona; Texas W. of Pecos R. and near Rio Grande in Val Verde Co.; Mexico south at least to San Luis Potosi.

Echinocactus horizonthalonius Lem.:
Mexico (Mesoamerica)
United States (North America)

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

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.

Plants normally unbranched. Stems pale gray-green to bright gray-blue, flat-topped or hemi-spheric and deep-seated in sub-strate, spheric with age or stoutly short cylindric (remaining hemi-spheric 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 var. nicholii L. D. Benson

Comments: Limestone soils of rocky hills in the desert. Chihuahuan Desert populations are common between 750 and 1675 m elevation of a variety of topographic forms and on both igneous and sedimentary substrates, most commonly on limestone and gypsum soils (Baker 2007). Arizona populations (var. nicholii) occur in Parkinsonia microphylla scrub with Ambrosia deltoidea, Carnegiea gigantea, Cylindropuntia acanthocarpa, Encelia farinosa, Fouquieria splendens, Krameria grayi, and Opuntia phaeacantha; and individuals occur between 750 and 1250 m elevation exclusively on limestone substrates of dissected alluvial fans, inclined terraces and saddles between ridges (Baker 2007).

Flowering Apr-Sep. Arid rocky slopes, primarily limestone; 600-1700(-2500) m; Ariz., N.Mex., Tex.; Mexico.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: Fifty-three estimated EO's (Benson 1982).

A small cactus species, growing only 10-12 inches high and about 6 inches wide, Echinocactus horizonthalonius have seeds that are cylindrical and roll down the side of the parent plant. Self dispersal is therefore evident, and what may look like one plant is actually the parent plant, acting as a nurse plant, with offspring surrounding it (Thornton 2007). Long distance dispersal by birds is not suspected given that fruits are heavily encased in a cage of spines (Thornton 2007). Finally, serotiny, or delayed self-dispersal, is documented in the genus Echinocactus, and is a bet-hedging strategy employed by plants in arid environments, so that seeds are dispersed when environmental conditions are favorable for germination (Peters et al. 2009).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 1
Species With Barcodes: 1

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Known from Arizona, New Mexico, Texas, and Mexico.

United States

Rounded National Status Rank: NNR - Unranked

Comments: Most cacti subject to horticultural collecting.