Tunas vendor in Pachuca (near Mexico City) |
Opuntia species are the most cold-tolerant of the lowland cacti, extending into western and southern Canada; one subspecies, Opuntia fragilis var. fragilis, has been found growing along the Beatton River in central British Columbia, southwest of Cecil Lake.
Prickly pears also produce a fruit that is commonly eaten in Mexico, known as tuna; it also is used to make aguas frescas. The fruit can be red, wine-red, green or yellow-orange.
Charles Darwin was the first to note that these cacti have thigmotactic anthers: when the anthers are touched, they curl over, depositing their pollen. This movement can be seen by gently poking the anthers of an open Opuntia flower. The same trait has evolved convergently in other cacti (e.g. Lophophora). [Wiki]