The threat of increasing hybridization of an endangered plant species, Purshia subintegra, in the Verde Valley, Arizona

Abstract

The existence of the endangered shrub Purshia subintegra may be threatened by hybridization with the more common P. stansburiana. In the Verde Valley, the range of the rare P. subintegra overlaps with the range of P. stansburiana, allowing introgression to occur. Although P. subintegra and P. stansburiana have many distinguishing characteristics, there are plants in the Verde Valley that have a combination of characteristics, making them difficult to identify. Using discriminant function analysis, we found that the parents and introgressed forms had detectable morphological differences that could be used to classify individuals, but only to 87 percent accuracy. Examining phenological and ecological differences increased our ability to detect introgressed forms. Purshia subintegra, P. stansburiana, and the introgressed forms overlap in their time of flowering in the spring, but P. stansburiana and plants showing characteristics of introgression can also bloom again in the summer. Comparing the presence of both parents and the introgressed forms in the Verde Valley in undisturbed limestone soil, roadsides, and washes, we found a significant difference in the habitat distributions of P. subintegra, P. stansburiana, and introgressed forms. Purshia subintegra showed no habitat preference; however introgressed forms occurred more frequently along washes and roadsides than in undisturbed habitat and P. stansburiana occurred in washes and on undisturbed limestone soil, but not along roadsides. Increased road construction and human disturbance in the rare P. subintegra habitat may favor the spread of introgressed forms along roads and increase the likelihood of more introgression. This has grave implications for the conservation of this rare species.

Parent Publication

• Southwestern rare and endangered plants: Proceedings of the Third Conference

Citation

Baggs, Joanne E.; Maschinski, Joyce. 2001. The threat of increasing hybridization of an endangered plant species, Purshia subintegra, in the Verde Valley, Arizona. In: Maschinski, Joyce; Holter, Louella, tech. eds. Southwestern rare and endangered plants: Proceedings of the Third Conference; 2000 September 25-28; Flagstaff, AZ. Proceedings RMRS-P-23. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 213-220.