Today we have a photograph of Peltigera gowardii. Richard Droker (aka wanderflechten@Flickr) took this photo looking down into a stream, and later uploaded it to the Botany Photo of the Day Flickr Pool. Thanks, Richard!
A member of the Peltigeraceae, Peltigera gowardii is a lichenized ascomycete. The cyanobacterium Nostoc forms an indistinct algal layer throughout the medullary tissues. This species is sub-erect, with a foliose thallus. The thallus is black when wet, and slate grey to black and papery when dry.
Peltigera gowardii is widely distributed throughout the mountain ranges of northwestern North America. The range extends from central/northern California northward to Oregon, Washington, and British Columbia with disjunct populations in Idaho and southern Alaska. This species is associated with older forests and watersheds on shaded rocks, often 0-2cm above water level.
It was only recently that Peltigera gowardii was described as a species. Previously, it was considered to be Peltigera hydrothyria—the morphologically similar eastern North American counterpart of Peltigera gowardii. In a taxonomic revision published in 2011, researchers reviewed Peltigera hydrothyria across North America. In addition to a molecular phylogenetic analysis, they evaluated the biogeography, ecology, morphology and chemical composition of lichens from both sides of the continent. This was to determine if they were or were not conspecific (the same species). They found that the eastern and western populations differed allopatrically (occurring in separate non-overlapping locations), chemically (the eastern group contains the secondary compound methyl gyrophorate and the western group does not), and molecularly. They also found that within the western population there were two distinct sequence types. This left them with a case where morphological characters supported a single widely-separated species, chemical analysis supported two species, and molecular data supported three species (where two have identical chemistry and overlapping ranges).
After consideration, it was determined that chemistry, biogeography, and molecular data are all in agreement in rejecting the circumscription of Peltigera hydrothyria based on morphology. It was then decided that at least one new species should be described to accommodate the western populations, and Peltigera gowardii is now recognized as a distinct species circumscribing two phylogenetic entities. More research is needed to determine if Peltigera gowardii can be further divided taxonomically (see: Lendemer, J. O’Brien, H. (2011). How do you reconcile molecular and non-molecular datasets? A case study where new molecular data prompts a revision of Peltigera hydrothyria s.l. in North America and the recognition of two species. Opuscula Philolichenum. 9:99-110).