Autor: Britton & Rose

“Breast-hedgehog (or urchin)” by analogy, because the species of the genus are globose and covered with spines.
A genus of solitary plants, globose to shortly cylindrical, radial spines usually covering the epidermis, aciculate, central spine sometimes absent. Spiralled low ribs, tubercles having a groove on the top, the areoles often with nectariferous glands.
Flowers diurnal, self sterile, appearing at the apex of stem, at the top of tubercles, with floral tube short or absent, white, yellow, brown, pink, magenta or purple, pollinated by bees (Megachile palmensis, Diadasia rinconis…) and diptera. Fruits scaly, elongated, basally dehiscent. Seeds ovate to kidney-shaped, finely papillose, black. Dispersion of seeds through myrmecochory and hydrochory.
The genus Echinomastus grows in reduced and localized colonies, in deserts or grasslands, hilly slopes facing south or east, on quite different soils, very often on limestone, also decomposed granite (£. erectocentrus), lavas rich in silicate or metamorphic rocks, in alluvial fans, from 200 m up to 2400 m in altitude, together with a few other cacti.
Mexico (Chihuahua, Coahuila, Durango, San Luis Potosi, Zacatecas), USA (Arizona, California, Nevada, New Mexico, Texas, Utah).

Currently 8 recognised species (among which three and maybe more are conflicting) +
two subspecies and one variety:
– Echinomastus durangensis (Runge) Britton & Rose 1922
– Echinomastus erectocentrus* (J.M.Coult.) Britton & Rose 1922 = Sclerocactus?
– Echinomastus gautii (L.D.Benson) Mosco & Zanovello 1997 = incertae sedis
– Echinomastus hispidus Davide & Zanovello 2004
– Echinomastus intertextus* (Engelm.) Britton & Rose 1922
– Echinomastus johnsonii* (Engelm.) E M.Baxter 1935 = Sclerocactus?
– Echinomastus johnsonii var. lutescens (Parish) Wiggins in Shreve & Wiggins 1964 = Sclerocactus?
– Echinomastus mariposensis* Hester 1945
– Echinomastus unguispinus* (Engelm.) Britton & Rose 1922
– Echinomastus unguispinus subsp. laui (G.Frank & Zecher) Glass 1998
– Echinomastus warnockii* (L.D.Benson) Glass & R.Foster 1975

References: "TAXONOMY of the CACTACEAE" -  ISBN 978-84-617-3723-9 (Vol. 1)