Eutrema penlandii Rollins (Brassicaceae) was originally described in 1950 from material collected in 1935 at Hoosier Pass in Park County, Colorado. Penlandís alpine fen mustard is a globally rare species restricted to continuously wet, alpine areas along a 25 mile stretch of the Continental Divide in the Mosquito Range. The closest relative to E. penlandii is the circumboreal E. edwardsii R. Brown, with the two species being disjunct by over 2000 km. In 1987, W.A. Weber subsumed E. penlandii into its North American congener, publishing the name E. edwardsii ssp. penlandii (Rollins) W.A. Weber. Since then, there has been considerable interest and debate among taxonomists and conservation biologists regarding the systematic relationship between the two taxa. Population genetic data revealed the two to be distinct (I = 0.914), but provided little further insight into the level at which E. penlandii should be recognized. In order to provide a clearer understanding of the taxonomic relationship of these taxa, morphometric data were collected for 34 continuous, quantitative reproductive and vegetative characters from 136 herbarium accessions of E. penlandii and E. edwardsii. Although the ranges for all 34 characters overlapped, Mann-Whitney tests revealed significant differences among the medians in 24 of the 34 characters, while t-tests revealed significant differences among the means in 19 of 26 normally distributed characters. Multivariate analyses provided further evidence with regard to the distinct nature of these taxa. The first three principal components deriving from a principal components analysis explained 61% of the variation in the data, with PCA scatterplots revealing discrete groupings corresponding to species boundaries. Similarly, discriminant functions analysis correctly classified the taxa 100% of the time. These data reveal the two taxa to be morphologically distinct and, coupled with the population genetic data, further support recognition of E. penlandii at the species level.

Key words: Brassicaceae, Eutrema penlandii