The overall form of Opuntia engelmannii is generally shrubby, with dense clumps up to 3.5 metres (11 ft) high, usually with no apparent trunk. The pads are green (rarely blue-green), obovate to round, about 15–30 cm long and 12–20 cm wide.
The glochids are yellow initially, then brown with age. Spines are extremely variable, with anywhere from 1-8 per areole, and often absent from lower areoles; they are yellow to white, slightly flattened, and 1–6 cm long.
The flowers are yellow, occasionally reddish, 5–8 cm in diameter and about as long. Flowering is in April and May, with each bloom lasting only one day, opening at about 8AM and closing 8 hours later. Pollinators include solitary bees, such as the Antophoridae, and sap beetles.
Scientific Name: Opuntia engelmannii
Common Name: Cactus Apple
Also Called: Cow's Tongue Prickly Pear, Engelmann Prickly Pear, Engelmann Pricklypear, Tuna; (Spanish: Nopal, Abrojo, Joconostle, Vela de Coyote)
Family: Cactaceae, Cactus Family
Synonyms: (Opuntia phaeacantha var. discata)
Size: Up to 4 or 5 or rarely 8 feet tall.
Growth Form: Shrub, Tree with short trunk; spreading to sometimes decumbent; stem segments yellow-green to blue-green, flattened (pads), glabrous, circular to obovate to rhombic.
Leaves: Spines evenly distributed on pad or absent, white to yellow, aging gray to blackish, spines straight to curbed; glochids widely spaced, yellow to red-brown aging gray or blackish.
Flower Color: Yellow throughout, or sometimes orange to pink to red and rarely whitish; flowers diurnal; filaments, anthers and style whitish to cream, stigma lobes yellow-green to green; fruit (called tunas) dark red to purple throughout, ovate-elongate to barrel-shaped, juicy, bleeding and staining, glabrous and spine-less, seeds tan to grayish.
Flowering Season: April to July.