PHENOTYPIC VARIATION IN STEPHANOMERIA EXIGUA SSP. CORONARIA (COMPOSITAE) AND ITS RECENT DERIVATIVE SPECIES “MALHEURENSIS”

Phenotypic variation in 33 quantitative characters was analyzed in Stephanomeria exigua ssp. coronaria (Greene) Gottlieb and its recent derivative species, presently called “Malheurensis,” grown in a series of experimental environments. The study was made to determine whether their high genetic identity, previously revealed by electrophoresis of a sample of their enzymes, was correlated with a high similarity in quantitative traits of morphology, size, growth rates, and fecundity. The electrophoretic evidence provided correct information about the relative variability, similarity, and phylogenetic relationship of the two taxa. Thus, 90% of the between-plant variance components from the analysis of variance were higher in ssp. coronaria and, therefore, concordant with its higher genetic variability. The between-environment variance components in the two species were similar in magnitude and when ordered, from smallest to largest, were nearly identical in ranking. The quantitative study provided important additional evidence. Ssp. coronaria grew more rapidly and produced more florets than Malheurensis in all of the growth conditions and also was found to grow larger than Malheurensis in their native habitat in eastern Oregon where they grow sympatrically. These and other results indicate that the persistence of Malheurensis in nature cannot depend on advantages of size, growth rates, or number of flowers produced per individual. The large differences between the taxa in the size of their seeds was used as the basis for a model to account for the continued persistence of Malheurensis.