Or is it Peltigera aphthosa? Only by peeking underneath can you be sure! This post was published as a lichen profile in the Winter 2013 issue of Aquilegia, newsletter of the Colorado Native Plant Society (Vol 37, No. 6). Back issues are available online at the CoNPS website..

Peltigera leucophlebia, Peltigera aphthosa

Broad, ruffled lobes would place the abundant “pelt” lichens among the most noticeable of our montane lichens, were it not for their usual cryptic brown and gray coloring. Fortunately three of our 15 species stand out, at least when wet, thanks to the chlorophytes that are their primary photobionts. Peltigera aphthosa and Peltigera leucophlebia (clear veins) are large lichens with bright green coloring that helps us spot them when the forest floor is moist. The 2-4 cm wide lobes radiate to form a thallus 30 cm or more across.

To distinguish these two species, you’ll probably have to take a peek at the underside. P. leucophlebia, as its name implies, has distinct veins that change from light colored near the margin to black toward the center. Carefully loosen the lichen from the soil or mosses to check for this. In P. aphthosa, the veins tend to be broad and undefined. The uplifted lobes bearing brownish apothecia have, in P. aphthosa, green cortex on the underside of these reproductive structures, but in P. leucophlebia, the cortex is absent or present only as green specks on the white background.

Fun fact: Round dark structures on the upper surface, called cephalodia, contain cyanobacteria, giving these lichens claim to a three-kingdom symbiosis.

Don’t be fooled: Species of Sticta look like Peltigera and are in the same family, but the underside is black with white spots instead of the characteristic veins. Our third green Peltigera, P. venosa, is smaller (less than 2 cm diameter) and each fan-shaped thallus consists of a single lobe, usually with black marginal apothecia.