Grant, V. and K.A. Grant. 1971. Dynamics of clonal microspecies in cholla cactus. Evolution 25:1 p. 144-155.
Original description (to be added)
Cylindropuntia ×kelvinensis is found in various Sonoran desert habitats of Arizona from approximately 500 m to 1000 m. They are open-crowned trees with whorled branches growing to 2 m tall. The terminal stems are generally easy to remove and are 5 to 13 cm long by 1.8 to 3 cm wide with prominent tubercles. The areoles have 0 to 8 spines which generally slightly overlap with those of adjacent areoles. The spines range in color from yellow to brown or sometimes pinkish to red-brown, and they age to brown-grey. The spine sheaths are whitish, sometimes with yellow tips. The flowers are rose to magenta with deep pink filaments, white styles sometimes with reddish-purple tips, and greenish-white stigmas. The fruits are yellow to purplish and form short chains. The fruits are usually sterile, as C. ×kelvinensis is mostly triploid (2n = 33). However, some diploid individuals (2n = 22) have also been found.
C. ×kelvinensis is a naturally occurring hybrid between C. fulgida and C. spinosior. More information on this species can be found in Baker and Pinkava’s 1987 paper, A cytological and morphometric analysis of a triploid apomict, Opuntia ×kelvinensis.