Typical forms of this species can be identified in the field by the bluish-black prothallus on which grey bounded soralia are formed. They contain perlatolic acid (UV+ white). However, many morphotypes (e.g. on rough bark, such as those found in the Czech Republic) have different morphology, where prothallus is replaced by a grey thallus and soralia gradually merge into a crust. This is reminiscent of the species Loxospora elatina, for example. Apothecia nor pycnidia have not been found in European material.
The species grows most frequently on smooth bark of deciduous trees, such as rowan and birch. However, it also colonises other tree species, including conifers, and sometimes passes onto wood. Its distribution has a strikingly oceanic character, so it is a very rare lichen in Central Europe. In the Czech Republic, the species has been found only in two localities in the Šumava Mts (protected areas Boubínský prales and Bílá strž), on spruce and beech.
This taxon most probably does not belong to the genus Mycoblastus (Malíček, unpubl.). Its phylogenetic affiliation is unclear and most probably it is a separate genus. Moreover, our preliminary data indicates that M. caesius, as it is defined now, covers two separate taxa.
Literature: Tønsberg T. (1992): The sorediate and isidiate, corticolous, crustose lichens in Norway. – Sommerfeltia 14: 1–331. James P. W. & Watson M. F. (2009): Mycoblastus Norman (1853). – In: Smith C. W., Aptroot A., Coppins B. J., Fletcher A., Gilbert O. L., James P. W. & Wolseley P. A. [eds], The Lichens of Great Britain and Ireland, p. 615–618, British Lichen Society, London.taxonomic classification:
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