Isozyme variation and species delimitation among diploid populations of the Puccinellia nuttalliana complex (Poaceae): character fixation and the discovery of phylogenetic species

Abstract

SummaryDavis, J. I. & Goldman, D. H.: Isozyme variation and species delimitation among diploid populations of the Puccinellia nuttalliana complex (Poaceae): character fixation and the discovery of phylogenetic species. – Taxon 42: 585–599. 1993. – ISSN 0040‐0262.Phylogenetic species, the minimal elements appropriate as terminals in phylogenetic analysis, are population systems that are differentiated by unique (i.e., diagnostic) character combinations. Within the predominandy polyploid Puccinellia nuttalliana species complex, two diploid taxonomic species are recognized on the basis of morphology. Isozyme variation was analysed in 11 diploid populations identified as P. lemmonii and one identified as the rare P. parishii, and variation profiles were generated for each population, reflecting each allele as either absent, present and fixed, or present and not fixed. Population Aggregation Analysis (PAA) grouped these populations into two distinct isozyme species that correspond precisely in membership to the species recognized previously on the basis of morphology; thus, isozyme patterns are congruent with those of morphology. Mean genetic identities among populations of P. lemmonii are not unusually high for conspecific plant populations, nor are genetic identities between populations of the two species unusually low.