(Photograph = Opuntia engelmannii, Stan Shebs)
Introduction
Opuntia engelmannii is a common and large Opuntia, found from western TX to far southeastern CA. It has been confused with other large opuntias.
The Details
O. engelmannii can be 3 to 6(8)-ft wide and up to 6-ft tall. Plants in northerly locations or at high altitudes are smaller. The pads are often 7(8)-inches across and may be up to 12-inches long. They are typically egg-shaped, oval, or circular. Cladodes are green or or sometimes barely blue-green, but are seldom dark green. Pads may even be yellow-green when stressed.
Areoles generally have (1)3 to 5 spines that are often white, tan, brown, or even pale yellow. The spines darken towards the base to brown (rarely red-brown) or even black, and they often fade to gray with age. Spines are variable, but generally less than 2 inches long and chalky appearing. The species ranges wide and far and there are types that might be considered varieties but which have not been validly described.
Related Reading: Opuntia Web