A distinctive new species of Thelocactus (Cactaceae) from Oaxaca, Mexico

Thelocactus tepelmemensis , a distinctive new species of Cactaceae from northern Oaxaca, Mexico, is described and illustrated. The new species is closest to T. leucacanthus but differs significantly from this and other species in the genus by a combination of morphological characters: smaller, red-purple flowers; stems with ribs consistently vertical; lower number of spines per areole, these being usually shorter; ovoid fruit; and seeds with conjunct micropyle. The new species is found in a narrow canyon growing on steep limestone rock faces protected from direct afternoon sun. The only known population appears to be locally common but geographically restricted.