Numerical Systematics of Comarostaphylis (Ericaceae: Arbuteae)

Abstract

Comarostaphylis is a genus of shrubs and small trees distributed from southern Cali- fornia to western Panama. Because taxa within the genus are often separated by quantitative rather than qualitative characters, populations were sampled in an attempt to provide an adequate rep- resentation of the pattern of variation. The resultant data, mostly on vegetative characters, were analyzed by a multivariate technique (canonical analysis or multiple discriminant analysis) and by a clustering technique (UPGMA) to provide evidence concerning infrageneric, specific, and sub- specific circumscriptions. A key is provided to the 10 species and the total of 16 taxa that are recognized as a result of the quantitative analyses as well as an interpretation of qualitative data. Comarostaphylis Zucc. (Ericaceae, Vaccinioi- deae, Arbuteae) is a genus of shrubs and small trees extending from southern California to western Panama, with its center of diversity in the Mexican highlands. The genus consists of 10 species; when subspecies are considered, a total of 16 taxa are recognized (Diggs 1981, 1986). It is a homogeneous group easily placed in the Arbuteae on the basis of a number of characters including anther morphology, fruit structure, and phytochemistry (Stevens 1971). Past treat- ments have often submerged the genus into Arctostaphylos, but the papillate fruit surface of Comarostaphylis unambiguously distinguishes it from the smooth-fruited Arctostaphylos. A num- ber of other characters, while not all absolute, also separate the two genera. Characteristic of Comarostaphylis (vs. Arctostaphylos) are the usu- ally dark purple or black, juicy fruit (vs. brown to red; mealy, granular or leathery), consis- tently fused nutlets (vs. fused or separate), lon- ger leaf length/width ratio, longer leaf blade/ petiole length ratio, usually cuneate leaf base (vs. obtuse to cordate or auriculate, quite vari- able), horizontal leaf orientation (vs. vertical) (Diggs 1981), and a distinctive flavonoid profile (Harborne and Williams 1973), as well as a usu- ally more mesic habitat and a southern distri- bution (primarily Mexico to Panama vs. mainly California). Generic relationships in the Ar- buteae have been studied by Diggs and Breckon (in Diggs 1981) who conclude that Comaro- staphylis is a distinct genus. The populations within Comarostaphylis show few qualitative differences in their flowers and fruits that can be used to recognize species; such reproductive characters are of secondary im- portance even in infrageneric classification. One is forced to use quantitative characters, both reproductive and vegetative, and to use statis- tical techniques to see the pattern of variation and to recognize taxonomic groups despite the blurring that results from this variation. There- fore, particular attention was given to sampling local populations so that the pattern of variation might be adequately represented. The resultant data were analyzed by a multivariate technique (canonical or multiple discriminant analysis) and by a clustering technique (UPGMA) to help in- terpret the pattern of variation. This paper re- views the evidence that these quantitative stud- ies provide concerning infrageneric, specific, and subspecific circumscriptions and concludes with a key to the taxa recognized as a result of the quantitative analyses as well as an inter- pretation of qualitative data.