Variation in stem and calyx trichomes in perennial Monardella (Lamiaceae)

The genus Monardella consists of approximately 30 species of plants in the mint family, occurring throughout the Western U.S., especially in California. The two major perennial species in Northern California are M. odoratissima which occupies the Sierra Nevada mountains above about 2000 feet elevation, and M. villosa which occupies the Coast Range. These two species are known to blend together (intergrade) in the vicinity of Snow Mountain near the Lake/Colusa County border. In an effort to better understand the morphological boundaries of these species, a study of calyx and stem trichomes by scanning electron microscopy (SEM) is being conducted. Trichome types, lengths, widths and densities are being measured on sepal tips, the calyx tube’s veins and intervein regions, and on the stem. Results indicate the presence of large and small glandular hairs, and unicellular and multicellular hairs. Variation in trichomes is not highly correlated with geography. Results bearing on the taxonomic separation of the two species will be presented