Griffiths, Bulletin of the Torrey Botanical Club 43(2): 90, 1916
Opuntia pyrocarpa is a commonly encountered plant in central and north-central Texas where it grows in deep limestone-derived soils. It may occur well into Mexico. Though we have not observed it in Oklahoma, it seems possible that the species is there. It is an ascending spreading plant to 24-inches tall. Often the main branches are prostrate but ascend at the ends. The cladodes are large, approximately 10(11) by 7(8) inches or they may be smaller in some plants. The cladodes are constricted at the base to form a short neck. The spines are porrect in new cladodes, but often slope down with age. Spines are present on the upper 50% to 60% of the areoles and are yellow darkening to a brown base. Spines are 1- to 1 1/2-inches long. The flowers are yellow with light-red centers or pure yellow. They have a white style tipped with a light-green stigma. The fruit is long, pyriform, and various shades of carmine, often with a purplish tinge outside and inside. The type location is Marble Falls, TX. See the original description.
O. pyrocarpa may create large plants that resemble piles of cladodes spread over 6-8 feet, making up for lack of height by achieving breadth. Several large plants growing together can create a formidable thicket. The species occurs with other species of Opuntia found in central Texas such as O. lindheimeri, O. macrorhiza, and O. orbiculata, etc.