Cladonia pyxidata and C. pocillum; genetic evidence to regard them as conspecific.

Species delimitation in lichen-forming fungi has been based largely on morphological differences of fungal structures and the lichen thallus with an assumption that morphology reflects hereditary changes. One of the distinguishing features between Cladonia pyxidata and C. pocillum (Cladoniaceae, Ascomycotina) is the shape of the primary squamules. Because these species may inhabit different types of soil the phylogeny of these species was examined in light of potential environmental influences from soil pH and photobiont. Samples were collected across North America, and soil pH was measured for a subset of samples. The nuclear ribosomal internal transcribed spacer of 49 fungal and 14 algal partners and a portion of the polyketide synthase gene of 18 fungi was sequenced and analyzed by phylogenetic methods. Restriction fragment length polymorphism (RFLP) profiles for 129 algae were examined for geographic variation and fungal specificity. Cladonia pyxidata and C. pocillum are not monophyletic but results show seven highly supported lineages. The photobiont and geographic distribution do not play a role in species delimitation. Soil pH shows a statistically significant difference between the extreme morphologies of the two species suggesting a possible link between morphology and environmental conditions.