Variability within and among Populations of Four Grass Species

Abstract

The importance of morphological variation for evolutionary and phylogenetic stud- ies is well recognized. This paper concentrates on morphological differences within and among population samples of several species of grasses to interpret potential for further differentiation. Analysis of gross morphology, a traditional tool of systematics, is coupled with numerical taxonomy to identify kinds of morphological differentiation among populations of species of four steppe grasses: Bromus japonicus, B. tectorum, Poa secunda, Pseudoregneria spicata. Floral and vegetative vari- ation in Poa secunda is consistent with apomictic differentiation. Floral characteristics in this species were responsible for more phenotypic divergence between populations (71%) than within popu- lations (35%), while vegetative traits were responsible for 29% of total variance between populations and 65% within populations. Inbreeding in the two Bromus species is not associated with any notable morphological differentiation between populations. Bromus tectorum appears to retain mor- phological uniformity throughout the area sampled. Character states for Pseudoregneria spicata ex- hibit varying degrees of plasticity depending on the population. This comparative study, concerned with differences and similarities in amounts and kinds of variation of morphological traits, repre- sents a first attempt to assess how morphological variation can be examined to detect the potential for some kinds of speciational events.