Thelocactus setispinus

This plant could be forgiven for being a little confused as to its identity. In the 19th century it started out, as did many other unrelated species, as an Echinocactus (Engelman 1845). Britton and Rose placed it in the genus Hamatocactus, by which name it is still often known. It has briefly been a member of Ferocactus before arriving in Thelocactus where it resides today.

Hamatocactus is actually an excellent name for the plant, ‘hamatus’ meaning hooked, is derived from the Latin word for fish-hook. The long (up to 27mm) central spines hook easily onto material, fingers etc. Setispinus is derived from ‘seta’ also Latin and meaning a bristle or hair.

0312 T setispinus1

Thelocactus setispinus does not look like a typical Thelocactus. It is the only member of Thelocactus the genus to have hooked central spines, and the only one without tubercles. Instead it has thin, somewhat wavy and slightly spiralling ribs. Whereas other Thelocacti have greenish or brownish fruit which dries out and splits open at the base, T. setispinus produces bright red, fleshy, berry-like fruit.

T. setispinus has extra-floral nectaries i.e. glands at the top of the areole which produce nectar. These are also present in T. bicolor, sometimes T. hastifer (but not always) and T. leucacanthus, which is considered to have the most primitive characteristics of the genus.

All these features place T. setispinus near Ferocactus, and the New Cactus Lexicon notes that it might represent an ‘ancient intergeneric hybrid’. The remaining member of the defunct genus Hamatocactus (Hamatocactus hamatacanthus) is now a Ferocactus.

In the wild T. setispinus is usually solitary although old specimens will clump in cultivation. It is found in southern Texas and north-eastern Mexico growing in lowland Mesquite scrubland areas.

Like all Thelocacti T setispinus has sumptuous flowers, shining yellow with a red throat, which can be up to 7cm (over 2 inches) across. It will flower easily in cultivation, the plant pictured has a succession of flowers throughout the summer and into the autumn. It requires the usual treatment for cacti, but might appreciate a little light shade in the hottest summer months, should we ever have them.

Copyright 2012 No part of this article or the accompanying pictures may be reproduced without permission

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