(Haworth) Haworth, Synopsis Plantarum Succulentarum 191, 1812
Opuntia stricta occurs on the shores of FL and other southeastern states. It may occur in the Caribbean, the Atlantic coast of Central America, and on the northern shores of South America, but some of these reports may refer to O. dillenii. Britton and Rose reported that the plant is found along the TX coast, and Weniger (1988) reported that the species may be found in Galveston Bay. The the reports of the plants in TX may have referred to O. anahuacensis because the authors have not observed the plant in TX. It does occur along the coasts of AL, MS, and GA. Often confused with O. dillenii, the two taxa are distinct and different. Read the original description. Various ploidies have been reported for O. stricta, but it is most commonly reported to be hexaploid.
Danny Green reports:
The cladodes on the Opuntia stricta are oval or spatulate, whereas those of Opuntia dillenii are obovate and/or rhomboid.
The areoles on Opuntia stricta tend to be flush with the surface of the cladode, whereas the areoles on Opuntia dillenii are elevated above the surface of the cladode. For this reason, the margins of the cladodes on Opuntia dillenii are scalloped or wavy unlike the to be smooth or straight margin of O. stricta.
The leaves of Opuntia stricta are shorter, thicker, and pointed upward (more parallel to surface of the cladode). In contrast, the leaves on Opuntia dillenii tend to be longer (though not all the time), slimmer, and pointed outwards (more perpendicular to the surface of the cladode).
The spines on Opuntia stricta tend to be straight and perpendicular to the surface of the cladode, and it is common for them to be mottled with brown and yellow. In contrast, the spines on Opuntia dillenii tend to be slightly curved (sometimes very noticeably curved) and usually yellow without mottling. Populations of O. dillenii in the Florida Keys may have mottled spines. John Kunkel Small thought that these Keys plants were a separate and distinct species and referred to it as Opuntia zebrina.
Opuntia stricta tends to be more shrubby in habit or even prostrate-ascending, usually between 2- to 5-ft tall. Exceptional specimens of O. dillenii may be 10-ft tall and have a very discernible trunk. However, it is more common to see shorter O. dillenii plants that are 3- to 6-ft tall. Irrespective of height, O. dillenii is seldom prostrate-ascending.
Finally, cotyledon morphology separates Opuntia dillenii from Opuntia stricta. The cotyledons on Opuntia stricta are heart shaped, half as long as those of O. dillenii, and pointed outward, whereas the cotyledons of Opuntia dillenii are oval, elongate, and pointed upwards.