Broe, Michael [1], Freudenstein, John [1].

Monotropa hypopithys L. (Ericaceae) is a distinct genus with well-defined species segregates at the molecular level.

The Monotropoideae are a herbaceous, achlorophyllous subfamily of the Ericaceae, within which 12 species in 10 genera are currently recognized. Most species are endemic to North America, however two---Monotropa uniflora L. and Monotropa hypopithys L.---have a much wider distribution in the Americas and Eurasia. We performed an extensive sampling of monotropoids across N. America, and here present molecular evidence for a revised treatment of this group based on ITS1, ITS2 and 26S (approx. 1200 bp). While the two Monotropa have long been recognized as a single genus, the phylogeny we present strongly supports the recognition of two distinct genera. Hypopitys (M. hypopithys) forms a monophyletic group with Pityopus, while Monotropa sensu stricto (M. uniflora) forms a monophyletic assemblage with Monotropsis and Monotropastrum (Asia). Hypopitys and Monotropa are further separated by the intervening genera Allotropa and Hemitomes. Within Hypopitys itself species and sub-species have been erected and subsequently synonymized to a remarkable degree. Small recognized five species in N. America, while in the most recent monograph Wallace rejected all such distinctions, choosing to synonymize some 80 putative species, subspecies and varieties in the Americas and Europe, noting 'there are no segregates that yet warrant taxonomic recognition'. Our analysis reveals five geographically circumscribed clades of Hypopitys in N. America alone---although the pattern is only partially congruent with Small's analysis---as well as a distinct Eurasian clade. This contrasts markedly with Monotropa, which exhibits no such structure in N. America at this level of phylogenetic resolution.
1 - The Ohio State University Herbarium, Evolution, Ecology and Organismal Biology, 1315 Kinnear Rd, Columbus, OH, 43212, USA.