Opuntia aurantiaca Lindl.
A low-growing succulent usually less than 30 cm tall; narrow stems grayish or dark green to purple, with brownish spines to 3 cm long; flowers yellow, fruits red with purple mottling.
native to Argentina, Paraguay, and Uruguay
naturalized in Australia and South Africa
warm-temperate and subtropical, sub-humid to semi-arid; along streams, grazing lands
Opuntia aurantiaca, a sterile hybrid, does not produce viable seed. Segments of the cactus break off, and reproduction is by dispersal of these spiny segments. The segments are dispersed by wind, attachment to animal hides and tires, or are carried by water. Another major means of dispersal is by humans, who use the plant as an ornamental and discard it in garbage. Segments that come to rest on soil form new roots from areoles on the segment's lower surface, and new stem segments from areoles on its upper surface. Dense stands of entangled spiny stems form an impenetrable barrier and harbor pests such as rabbits. Opuntia aurantiaca has become a serious pest in Australia and is one of the worst weeds in South Africa.