Great Basin Naturalist


Populations of Purshia in central Arizona are intermediate in some characters between Purshia subintegra, an endangered species, and Purshia stansburiana, the common cliffrose. These intermediates may represent forms derived from a history of hybridization and introgression between putative parent species. Morphological data were obtained from 216 pressed speciments of P. subintegra, P. stansburiana, and introgressed forms. Over 50 separate discriminant function analyses (DFA) and principal components analyses (PCA) were run on numerous combinations of raw and log-transformed data. The best variable suite, providing the clearest discrimination between groups, used log-transformed data on 15 morphological characters, but DFA post-hoc identifications were 90–100% correct with only 7 characters using raw data. DFA distinguished four separate nodes of variation. Two groups consisting of 122 P. subintegra and 29 P. stansburiana were easily discriminated in DFA and were distinguished in PCA as well. Introgressed forms were consistently identified in two much less well-defined groups of 46 and 19 specimens. Introgressed forms are not intermediate between the two supposed parents in some characters, appearing most similar to P. stansburiana in most measured characteristics. Principal distinguishing characteristics of the four groups are as follows: P. subintegra—usually eglandular, has 0–2 leaf lobes and short hypanthia-pedicels; P. stansburiana—always abundantly glandular, has 4 leaf lobes and short hypanthia-pedicels; the introgressed from "Tonto" is usually eglanduluar, has 4 leaf lobes and long hypanthia-pedicels; the introgressed form "Verde" is usually glandular, has 4 leaf lobes and slightly shorter hypanthia-pedicels.