| | The genera of Cactaceae |
~ Thelocactus, cf. Hunt (1967)
The plants condensed-cactoid; low and very compacted in their entirety. The plants’ appearance dominated by crowded interlacing areolar structures obscuring any tubercles, ribs or furrows. The stems very spiny; globose, or shortly cylindric; not apically depressed. The plants usually unbranched; erect; mostly solitary; to 0.05–0.37 m high. The stems not segmented; ribbed and grooved, or not ribbed and grooved. The ribs when present, borne spirally; low. The grooves deep and narrow. The plants conspicuously tuberculate. The tubercles longitudinally grooved adaxially from the areole towards their ‘axils’. The tubercular groove short, extending less than halfway to the ‘axil’. The tubercles spirally disposed. The areoles associated with tubercles. The components of adjacent areoles so extensively covering the mature plant body as to obscure any ribs or furrows. The areoles spirally disposed; with the abaxial spine cluster at the tubercle tip connected to the adaxial floriferous meristem nearer its axil by a recessed linear isthmus or a ridge; often associated with extra-floral nectaries; without glochids; with spines. The spines clustered; 12–40; 0.4–4 cm long; with radials and centrals differentiated (or centrals sometimes lacking). Central spines (0–)1–9. Radial spines 9–32. The spines stiff; straight; terete (acicular, often interlacing). The mature stems leafless.
Flowering during the day. The flowers solitary, or aggregated; terminal; one per areole (borne at the tips of the tubercles); funnelform; sessile; medium-sized; 2–6 cm long; regular. The receptacle scarcely produced beyond the ovary to not produced beyond the ovary; not naked; with scales; spineless. The pericarpel with scales. The hypanthial tube if present, not naked; with scales; spineless. The perianth white, or pink, or purple. The perianth segments relatively short, broad; blunt, or pointed, or apiculate. Stamens numerous; not exserted.
The mature fruit to 1 cm long (in the one species recorded ...); ellipsoidal (elongate); before drying, green; not naked (scaly); without spines; non-fleshy when mature; dehiscent; dehiscing vertically by one slit, or dehiscing vertically by more than one slit, or dehiscing via basal pores (? - "via a basal pore, vertically, or by slits"). The seeds black; ovoid, or reniform; not encased in bony arils. The testa tuberculate. Cotyledons reduced or vestigial.
Natural Distribution. Southwestern United States and northern Mexico.
Classification. 7 species. Subfamily Cactoideae. Tribe Cacteae.
Images. • Echinomastus erectocentrus and E. unguispinus: Britton & Rose (1922). • Echinomastus intertextus: Britton & Rose (1922). • Echinomastus intertextus (as dasyacanthus), with Thelocactus macdowellii (as Echinomastus): Britton & Rose (1922).
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2018 onwards. The genera of Cactaceae: descriptions, illustrations, identification, and information retrieval. Version: 14th November 2021. delta-intkey.com’.
