has several differences from most other hedgehog species; it is very frost tolerant, grows much further north, into Wyoming and South Dakota, and has smaller flowers which appear along the stem rather than near the tip.
Plants are globular or cylindrical, up to 12 inches tall but usually rather less, and between 1 and 3 inches in diameter. Stems remain single or form small clumps of a dozen or so members. Ribs number between ten and 20. Spines are variable in color, short and quite numerous, straight or slightly curved; there may be up to 45 radials, and from 0 to 17 centrals; maximum length just over an inch. Flowers, up to one inch long, are usually yellow to pale brown, darker brown to red for west Texas populations.
A number of variants of echinocereus viridiflorus have been proposed, differing in spine characteristics and flower color, though they not recognised by all authorities. The most distinctive, usually considered a separate species, is echinocereus chloranthus
; this has the greatest number of central spines (four or more), and the spines generally obscure the green stem. Brown- or red-flowered specimens from Big Bend National Park in Texas have veen classed as echinocereus russanthus
. Other variants include correllii, cylindricus, davisii
and nova; like most species that occur over a wide geographical range there are often differences in specimens from disparate locations.