April 2011 Plant Highlight: Theocactus tulensis

by Brian Kemble

Thelocactus is a genus of about 12 to 15 species of globular cacti native to northeasteren Mexico, with one species extending across the border into Texas.  They are generally of modest size, though the largest species may be up to 10” across (25 cm).  Most are single-headed, but some are clump-forming.

One kind of Thelocactus which does well at the Ruth Bancroft Garden is Thelocactus tulensis, native to the Mexican states of San Luis Potosi and Tamaulipas.  These chubby cacti have spine clusters atop rounded or conical tubercles.  The spine length and density varies, but the spines are never so thick as to obscure the plant body, which is green to gray-green, sometimes with a reddish tinge.  Plants may be single or clumping, with heads from 4 to 7 inches across (10 – 18 cm)

The flowers of Thelocactus tulensis emerge in spring at the top of the plant, with the flower color varying from white to pink to pale yellow.  After the initial flush of flowering in early spring, plants often produce subsequent flushes at intervals through the spring months.  The flowers are 1¼ to 2 inches or more in diameter (3 to 6 cm).