Echinocactus uncinatus Galeotti, Abbild. Beschr. Cact. 2: plate 18. 1848

Varieties 2 (1 in the flora): sw United States, Mexico.

Without its reddish flowers or fruits, Glandulicactus uncinatus resembles Ancistrocactus brevihamatus and, especially, Ferocactus hamatacanthus. The variable areoles of the three species are similar except for the diagnostic hooks on the abaxial radial spines of Glandulicactus.

Glandulicactus uncinatus differs from Hamatocactus bicolor of the Tamaulipan thorn scrub by its strongly crenate ribs, greatly elongated areoles on sexually mature plants, dome-shaped instead of peg-shaped areolar glands, broadly funnelform-campanulate receptacle, tricolpate pollen, relatively large perisperm, and strongly curved embryos. The peculiar dark red to russet or brownish purple tepals of Glandulicactus contrast with the bright yellow inner tepals of Hamatocactus, but both genera share showy red fruits and hooked central spines. Straight-spined variants are well known in Hamatocactus bicolor, but not reported in Glandulicactus, where even the abaxial radial spines are consistently hooked.