Trichome morphology relates to taxonomic diversity in Monardella (Lamiaceae) in the lower Snake River Watershed of Idaho and Oregon, USA: Taxonomic studies in Monardella (Lamiaceae) VI

Monardella is a western North America genus ranging from the Rocky Mountains to the Pacific Ocean and from southern Canada to the southern tip of Baja California Sur. The levels of unrecognized and cryptic taxa within Monardella are similar to other taxonomically complicated western North American genera, such as Eriogonum (Polygonaceae), Penstemon (Plantaginaceae), and Oreocarya (Boraginaceae). We present variation in trichome morphology as a taxonomic tool within Monardella, being comparable in importance to trichome variation in other plant families and genera (e.g., Brassicaceae, Draba; Loasaceae, Mentzelia; Solanaceae, Solanum). Trichome morphology within Monardella is a useful character to differentiate taxa and resolve taxonomic ambiguities. We present nomenclatural novelties and revisions for Monardella occurring in the Hells Canyon region along the lower Snake River of west-central Idaho and northeastern Oregon. We introduce the following taxonomic and nomenclatural changes. Monardella odoratissima Benth. var. neglecta Cronquist is recognized as a later homonym; a new name and rank are presented for it: M. perplexans Elvin, R. B. Kelley, & B. T. Drew. Two new species are described: M. kruckebergii Elvin, R. B. Kelley, & B. T. Drew and M. walwaamaxsia Elvin, R. B. Kelley, & B. T. Drew.