Sixty stands of Scirpus acutus Muhl. and S. validus Vahl from five areas in southern Manitoba were examined to determine (i) whether the two were morphologically distinguishable within the region studied and, if so, (ii) which morphological characters were the most useful to separate them. Thirteen characters were measured on pressed and living specimens. From these, six bimodally distributed characters were objectively selected to calculate a biometric index for each specimen. Mean indices for 56 stands were separable into two groups, indicating that they contained pure populations of one taxon. Three stands had mixed populations, and one contained morphologically intermediate individuals. The two taxa can be consistently identified using a combination of six characters. Scirpus acutus has an inflorescence < 47 mm long, less than seven primary rays, no secondary rays, clusters of more than five spikelets, aerenchymal lacunae < 0.9 mm in diameter, and dark green culms in fresh specimens. In contrast, S. validus has inflorescences > 80 mm long, more than 13 primary rays, secondary, tertiary, and occasionally quaternary rays present, spikelets generally in clusters of one to three, aerenchymal lacunae > 1.5 mm in diameter, and light green culms in fresh specimens. Data from Manitoba populations support their status as separate species.
Taxonomic Identity of Carpinus dayongina Franchet (Betulaceae)