(Engelmann & J. M. Bigelow) Britton & Rose, Smithsonian Miscellaneous Collections 50: 535, 1908
Lectotype (O. missouriensis trichophora); Lectotype (O. polyacantha trichophora); Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Drawing (The Botany of the Expedition, 1856, plate XV No. 1-4 [O. missouriensis trichophora])
From Powell and Weedin: page 182
Opuntia trichophora is a prickly pear cactus that has been treated as a variety of O. polyacantha. Herein we treat it as a stand-alone species of prickly pear. Cacti are small, 10-25 cm tall and with relatively small pads. The areoles on this prickly pear are closely spaced with about a dozen slender spines (6-17). The longest spines may be hairlike and 4-8 cm long. The other spines are 1-3 cm long and are often appressed. The longer spines are typically pale.
Flowers of this Opuntia are yellow, 4-7 cm long and 4-5 cm wide, but smaller flowers may be produced. The filaments are often pale or barely green-tinted to cream-colored or even pale yellow. They style is cream to pinkish and about 2 cm long and only slightly bulbous at the base. The 8 stigma lobes are 3 mm long and dark green. The slender pericarpel has spiny or hairy areoles. The fruits are dry and smallish, very spiny at maturity. The fruits are obconic or nearly so and 1.9 to 2.5 cm long with many areoles. The umbilicus may be up to 8 mm deep. There are few (8-10) large seeds per fruit, irregularly discoid, 6-6.8 mm in maximum diameter, 1.5-2 mm thick, with a beaked margin 1-2 mm wide.
The pads of this Opuntia are variously shaped: broadly ovate, orbiculate, obovate to narrowly obovate and flat. The pads are often 7-13 cm long and 5.5-11 cm in diameter and about 1 cm thick, but smaller pads occur. The areoles are close together: 0.6-1.3 cm apart. Spines are present in almost all of the areoles.
O. trichophora is similar in overall appearance to O. diploursina. Both may have spines that are very slender and flexible, forming long hairs and areoles that are close together. Some plants may not have long hair-like spines and can have a wooly appearance with many short spines. See the original description. O. trichophora is diploid.
Dave Ferguson writes:
Some individuals may have slender spines longer than 14 cm. Sometimes the hair-like spines are located only on the underside of the plant, are few in number, and are early deciduous. Occasionally plants have no discernible long hairs. The smallish pads are frequently obscured by the presence of many spines. The seeds are irregular in outline and large.
O. trichophora often grows on hot rocky slopes or cliff faces in mountainous or otherwise dissected terrain, but it can grow on gypsum soils or even sandy soils in grasslands or pinon-juniper woodlands. Some populations grow in baking hot conditions (e.g., on south- or southwest-facing sunny basalt cliffs). O. trichophora grows above 3000 ft and often grows at 5000 ft or higher. It has been anecdotally reported at 9000 ft.
This Opuntia occurs throughout much of Colorado Plateau and north into WY along Flaming Gorge. It may be observed east of the central mountains of UT, on the western side of CO, in northern AZ, in most of NM west of the Great Plains, in trans-Pecos TX, and into Mexico.