Chromosome numbers in Chihuahuan Desert Cactaceae. III. Trans-Pecos Texas.

Chromosome numbers are reported for 112 collections of Cactaceae, including 102 collections of Opuntia. Reports are presented for 33 species in five genera and a total of 36 taxa. Two specimens were sterile. Emphasis was given to the documentation of intraspecific ploidy-level consistencies and differences, because of the current poor state of knowledge about the populational integrity of chromosome numbers in Trans-Pecos cacti and because information about ploidy levels is taxonomically significant particularly in certain genera of Cactaceae. First reports are presented for six taxa, including Opuntia aureispina (2n = 11 II), O. tortispina (2n = 33 II), and Ancistrocactus tobuschii (2n = 11 II). Chromosome numbers are now known for all but one or two of the ∼104 currently recognized cactus taxa in Trans-Pecos Texas.