Opuntia robusta in length. Yellow, sessile flowers with a fleshy base are produced on the edges of the upper stem segments. These are followed by barrel-shaped fleshy fruits which are pink or purple and up to long. The species was first formally described in 1837 in "Enumeratio Diagnostica Cactearum hucusque Cognitarum". It has naturalised in the states of South Australia, New South Wales, Queensland and Victoria in Australia. Opuntia robusta Opuntia robusta, the wheel cactus, nopal tapon, or camuesa, is a species of cactus in the Cactaceae family. It is native and endemic to central and northern Mexico to within 100 miles
Opuntia readily between species. This can make classification difficult, yielding a reticulate phylogeny where different species come together in hybridization. Also, not all species listed here may actually belong in this genus, meaning that "Opuntia" is not a monophyletic group. "Opuntia" also has a tendency for polyploidy. The ancestral diploid state was 2n=22, but many species are hexaploid (6n = 66) or octaploid (8n = 88). Chollas, now recognized to belong to the distinct genus "Cylindropuntia", are distinguished by having cylindrical, rather than flattened, stem segments with large barbed spines. The stem joints of several species, notably the jumping cholla ("Cylindropuntia