Phenotypic Plasticity and the Selection of Taxonomic Characters in Puccinellia (Poaceae)

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Abstract
Phenotypic plasticity diminishes a character''s taxonomic utility because the environmental contribution to phenotypic variation obscures genetically based relationships. To evaluate potential taxonomic characters of Puccinellia, divided clones representing several putative taxa were grown under a series of salt- and drought-stress treatments representing naturally encountered environmental conditions. The resulting variation in 41 characters was partitioned by analysis of variance (ANOVA) into genetic and environmental components. Logarithmic transformation facilitates comparisons of variance levels among characters. Analogous nonparametric tests were used to analyze 40 characters not amenable to ANOVA. Levels of variance among genotypes and among treatments (phenotypic plasticity) are continuous in distribution and highly variable in magnitude. Attributes of the spikelet dominate the list of characters best meeting the criteria of high genotypic variability and low plasticity. Ratios representing shapes and relative sizes tend to be more reliable than their component simple measurements. This analysis empirically confirms the importance of many characters emphasized in grass systematics and suggests characters for Puccinellia that previously have not been recognized as significant.