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![Ascospore dimensions (in µm) and septation in yellow species of Rhizocarpon in Snowdonia, not including R. geographicum s. lat. Notes: [a] Error estimates for R. viridiatrum and R. intermediellum are standard deviations of the means for single specimens. [b] Spores of R. alpicola and R. eupetraeoides are infrequently 3-or 4-celled, those of R. intermediellum infrequently 2-or 3-celled. [c] Values are number of cells visible in optical section per spore.](profile/Stephen-Clayden-2/publication/370761476/figure/tbl1/AS:11431281158246522@1684087927475/Ascospore-dimensions-in-m-and-septation-in-yellow-species-of-Rhizocarpon-in-Snowdonia.png)
Ascospore dimensions (in µm) and septation in yellow species of Rhizocarpon in Snowdonia, not including R. geographicum s. lat. Notes: [a] Error estimates for R. viridiatrum and R. intermediellum are standard deviations of the means for single specimens. [b] Spores of R. alpicola and R. eupetraeoides are infrequently 3-or 4-celled, those of R. intermediellum infrequently 2-or 3-celled. [c] Values are number of cells visible in optical section per spore.
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Citations
... The interspecific and infraspecific variation in the R. geographicum group has not been clearly resolved by morphological studies. Clayden (2004) concluded, after studying the yellow species of Rhizocarpon in North Wales, that molecular techniques were necessary to clarify the systematics of the complex. Timdal & Holtan-Hartwig (1988) proposed the synonymy of various R. geographicum group species, based mainly on chemical characters, 1-septate spores (yellow and non-yellow species) and dark and muriform spores (nonyellow species). ...
... The yellow-green pigmented group in Rhizocarpon is currently recognized as containing 26 species, defined by the I+ bluebright violet reacting medulla, an epithecium without blackish granules, and muriform ascospores. The taxonomy of the group has only undergone minor changes during almost 60 years but has remained controversial (Poelt 1988), with specialists frequently recognizing that the group needed a thorough revision (Thomson 1967;Feuerer 1978;Poelt 1988;Clayden 2004;Roca-Valiente 2013). One of the most problematic aspects is that descriptions and taxonomic concepts differ between authors, making confident identification often either very difficult or impossible with existing keys. ...
As part of a comprehensive revision of the
Rhizocarpon geographicum
species group using molecular and morphological approaches, we examined the name-bearing types of 15 species. We report ambiguities and inconsistencies with the reported features of some type specimens, original descriptions, and circumscriptions employed in keys for the identification of taxa within the complex. The reporting of chemical reactions and some morphological characters was found to be inconsistent and likely to lead to errors of identification. This is unfortunate in view of the widespread use of the complex in glaciology for lichenometry. Issues surrounding the typification of the basionym
Lichen geographicus
are clarified, and the epitype is illustrated. The complex nomenclatural situation regarding the name
Rhizocarpon lecanorinum
and its typification is also made clear. The examination of the anatomical and morphological characters presented here needs to be considered together with molecular phylogenetic information to provide a more informed new taxonomy of the group.
