Previous phylogenetic analyses of Lepidium included only a few accessions of L. montanum, L. flavum, and L. fremontii to represent western North American species. Two additional species endemic to southwest Idaho have posed both taxonomic and conservation questions regarding their species status. Lepidium papilliferum was originally described as a variety of L. montanum, is morphologically similar to L. montanum, and is found in small scattered populations in southwest Idaho. The plant is restricted to specific edaphic conditions known as slick spots where high clay content creates conditions amenable to L. papilliferum, but to few other species. Resolving whether the populations of L. papilliferum merit species status distinct from L. montanum is a vexing question and phylogenetic analyses can assist in resolving this issue. Like L. papilliferum, L. davisii has specific edaphic requirements and is found in playas, areas similar to slick spots, but larger and with deeper soils. Unlike L. papilliferum, L. davisii is morphologically distinct from L. montanum and has posed less of a taxonomic quandary. Previous phylogenetic studies have shown that American species of Lepidium are derived from an ancestral allopolyploid species. In this study we have expanded previous analyses to include L. papilliferum, L. davisii, and several accessions of L. montanum along with published sequences of ITS, cpDNA, and PISTILLATA first intron. The western North American species form a monophyletic group with L. davisii sister to the remainder of the clade. Within this clade, L. papilliferum and L. fremontii are each monophyletic and sister to each other, but are imbedded within a paraphyletic L. montanum.
Available at: http://works.bepress.com/ian_robertson/7/