Reassessment of subspecific taxa within Pediocactus peeblesianus (Cactaceae) by multivariate analysis of morphological characters

Abstract

A study was undertaken to determine whether there are groups of populations within Pediocactus peeblesianus that when considered collectively possess combinations of morphological character values that are significantly different between or among other groups and whether any such groupings correlate with geography. A total of 323 individuals were measured for 17 stem characters in 11 populations, including three populations of the outgroup, Pediocactus sileri. The morphological data suggested no practical geographic manner in which to segregate taxonomic groups of populations within P. peeblesianus. A weak morphological cline occurred from west to east, in which central spines increased in number and length, and radial spines decreased in thickness. Values for four characters correlated significantly with stem diameter, indicating that a significant amount of the morphological variation within P. peeblesianus can be explained by plant size. Historically, the taxon P. peeblesianus var. peeblesianus was evidently based on neotenous individuals occurring on very shallow soils, while P. peeblesianus var. fickeiseniorum was based on individuals occurring on deeper soils farther west along the cline. In light of our findings, we see no reason to recognize infraspecific taxa within P. peeblesianus.