Engelmann's Pricklypear

O. engelmannii is generally shrubby, with dense clumps up to 3.5 metres (11 ft) high, usually with no apparent trunk. The pads, or cladodes, are green (rarely blue-green), obovate to round, about 15–30 cm long and 12–20 cm wide. In the Sonoran Desert, terminal pads face predominantly east-west, so as to maximize the absorption of solar radiation during summer rains. The cladodes make up the stem and are the primary photosynthetic structure. O. engelmannii typically grows in high altitude desert, where lower atmospheric pressure increases water stress and may make gas exchange difficult , leading to a reliance on CAM photosynthesis for more efficient gas exchange and less water lost in the process . The glochids are initially yellow and brown with age. Cactus spines are nonvascularized, modified leaves that arise from areoles and are usually in clumps. Spines are extremely variable, with anywhere from 1-8 per areole, and are often absent from lower areoles; they are yellow to white, slightly flattened, and 1–6 cm long. Spines harden from the top down and develop a waxy cuticle. The spines do not photosynthesize. The spines primarily serve as defense. …

O. engelmannii is native to sub-tropical regions of North America. It prefers hot, dry conditions, but is more frost-tolerant than other species of Opuntia. O. engelmannii range extends from California to Louisiana in the United States, and from Sonora (state) and Chihuahua (state), to the Tamaulipan matorral in north and central Tamaulipas. Although found occasionally in the Mojave Desert, it tends to be replaced by Opuntia basilaris, which does not need the summer rain. Naturalised in southern and eastern Africa, including Loisaba in Kenya, where they are considered invasive. O. engelmannii was also reported in Spain in the early 2000s and remains invasive.

The fruits were a reliable summer food for Native American tribes. The Tohono O'odham of the Sonoran Desert in particular classified the fruits by color, time of ripening, and how well they kept in storage. O. engelmannii is cultivated as an ornamental plant, for use in drought tolerant gardens, container plantings, and natural landscaping projects. O. engelmannii has also been used as a living hedge and cattle fodder. These functions, paired with a capacity to survive drought, led to its import to various locations in Africa.