A lichenicolous species, Calicium ramboldiicola, growing on Ramboldia elabens is described. In phylogenetic analyses with 22 Calicium taxa, based on 121 sequences from five DNA regions (mtSSU, Mcm7, nuITS, nuLSU, β-tubulin), the new species formed a strongly supported clade with C. abietinum and C. verrucosum. Although the ascomata of the new species resemble miniatures of those of C. abietinum, no morphological synapomorphies for this clade were found. Calicium ramboldiicola is known from boreal and hemiboreal areas of northern Europe and north-eastern North America. It is the second known lichenicolous species of Calicium and the first found on a lichen in the Lecanorales.

The genus Rinodina (Physciaceae), with approximately 300 species, has been subject to few phylogenetic studies. Consequently taxonomic hypotheses in Rinodina are largely reliant on phenotypic data, while hypotheses incorporating DNA dependent methods remain to be tested. Here we investigate Rinodina degeliana/R. subparieta and the Rinodina mniaraea group, which previously have not been subjected to comprehensive molecular and phenotypic studies. We conducted detailed morphological, anatomical, chemical, molecular phylogenetic and species delimitation studies including 24 newly sequenced specimens. We propose that Rinodina degeliana and R. subparieta are conspecific and that chemical morphs within the R. mniaraea group should be recognized as distinct species. We also propose the placement of the recently described genus Oxnerella in Physciaceae.

Ascospore germination, thallus initiation, and areole and prothallus development in the lichen Rhizocarpon lecanorinum Anders were examined using light, fluorescence and scanning electron microscopy. The ascospore germ hyphae remain very short and do not form a prothallus-like mycelium. Instead, a compact soredium-like granule develops directly from sporeling contact with a compatible species of Trebouxia. Diffuse initial stages involving non-trebouxioid algae are lacking. The onset of thallus differentiation is marked by the deposition of rhizocarpic acid in an incipient cortical layer within the apical part of the granule. As pigmentation and cortex-formation transform this structure into a typical areole, radiating prothallus hyphae are simultaneously initiated from its basal margin. Most areoles formed subsequently in the marginal prothallus lack subtending melanized hyphae and apparently stem from overgrowth by the prothallus of photobiont cells on, or in, the substratum. Apothecia reach maturity in thalli as small as 2 mm in diameter. It is proposed that the lack of diffuse hyphal growth in sporelings and telescoped morphogenesis of R. lecanorinum are part of a life history strategy geared to precocious, heavy investment in ascospore production. The R. lecanorinum–Trebouxia symbiosis has a number of features which make it well-suited for further studies of the life history and development of prothallus-forming crustose lichens with sexually reproducing mycobionts.

Intraspecific thallus interactions in mixed populations of Rhizocarpon lecanorinum and R. geographicum in North Wales are described. In contrast to the most commonly occurring morphotype of R. geographicum, which forms mosaics comprised of sharply delimited individual thalli, R. lecanorinum thalli consistently merge with one another at intraspecific contacts, leaving no visible trace of their initial boundaries. On the analogy of mycelial interactions in populations of wood-rotting and other non-lichen-forming fungi, it is postulated that these differences are the outcome, in R. geographicum, of somatic incompatibility between distinct genotypes, and in R. lecanorinum of somatic compatibility among genetically identical or very closely related thalli. Possible mechanisms for the evolution of clonal population structure in R. lecanorinum and links between somatic interactions and reproductive output in these species are discussed. Facultative parasitism of R. lecanorinum by Schaereria fuscocinerea, and resistance to such parasitism by cooccurring R. geographicum, are also documented.