Perspectives on Chemotaxonomy: Molecular Data Confirm the Existence of Two Morphologically Distinct Species within a Chemically Defined Lepraria caesiella (Stereocaulaceae)

Lepraria caesiella as currently circumscribed includes two sets of populations with different thallus morphologies. The populations are chemically identical but differ ecologically and are rarely sympatric. A phylogeny was inferred from ITS1, 5.8S, and ITS2 sequence data generated from a geographically broad sampling of the populations with each thallus type. Two strongly-supported clades were recovered that correlate to the two different morphotypes present within the species. Thus, L. caesiella is restricted to populations with aggregate thalli. Populations with placodioid thalli are formally described herein as a new species, L. harrisiana. A detailed taxonomic treatment of both taxa is presented.