Variation and integration in the rare grass Achnatherum (Oryzopsis) hendersonii: phenotypic comparison with parapatric common congeners

Abstract

Phenotypic properties indicating levels of variation and integration were compared among three populations of a rare bunch grass, Achnatherum (Oryzopsis) hendersonii (tribe Stipeae), and one parapatric population of each of its common relatives Achnatherum (Stipa) lemmonii and Achnatherum (Stipa) thurberiana, sampled from the Colockum Pass area of central Washington, U.S.A. Twenty-five randomly selected plants from each population were measured for both vegetative and spikelet features. The vegetative features were represented by morphometric measurements taken from one leaf on a tiller and the flag leaf on a flowering culm. The spikelet features were based on two to eight spikelets per plant. The three data sets were analyzed separately to compare population level variation both among individuals and among variables (variable covariation). Phenotypic variation among individuals is lowest for A. hendersonii in estimators of both size and shape; within-individual phenotypic variation, as evaluated through among-variable correlation coefficients, is highest for A. hendersonii and lowest for A. thurberiana. The lower level of among-individual variation for A. hendersonii is consistent with biological beliefs about rare species; its higher among-variable variation may indicate less precise control of integration. Key words: rarity, morphological variation and integration, Poaceae, Achnatherum.