The Opuntiae of the Big Bend Region of Texas

Anthony, Margery

The area studied encompasses Jeff Davis, Presidio and Brewster counties, Texas with the latter receiving most detailed consideration. Diversity of topography has produced a corresponding variety of habitats with at least thirty-five plant associations and many distinct populations of Opuntiae. Distinguishing characteristics for species include growth habit, distance between areoles, form and color of spines, presence or absence of bristles, type of fruit, size of seed, and width of aril. Variations of characteristics within species are particularly expressed in number of spiniferous areoles on a joint, number of spines per areole, and length of individual spines. A key to the thirty-one species, varieties and hybrids found in the Big Bend region precedes discussion of these entities. Four new varieties are described: O. imbricata var. argentea, O. lindheimeri var. chisoensis, O. macrocentra var. minor, and O. rufida var. tortiflora. Each of these may be thought of as a potential source of new species. Three new hybrids are presented: O. engelmanni x phaeacantha, O. grahamii x schotti and O. kleiniae x leptocaulis. O. spinosibacca, the only known endemic species of Opuntia of the Big Bend region, is newly described. An example of disjunct distribution is found in O. tunicata which occurs here far from its closest recorded station in Saltillo, Coahuila. Its dwarf and typical forms suggest perpetuation of somatic differentiation in vegetatively reproduced clones.

The Opuntiae of the Big Bend Region of Texas

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