Field of Science


Psora decipiens, copyright Troy McMullin.

Just a very quick one today. The photo above is of a member of the Psoraceae, a group of lichens sometimes referred to as 'fishscale lichens'. As their vernacular name indicates, Psoraceae are characterised by a scaly appearance, together with a preference for growing on soil or rock crevices (Ekman & Blaalid 2011). The scaly appearance also gives the family its botanical name: Psora comes from the Greek for 'itch'.

Psora vallesiaca, copyright Leif Stridvall.

Molecular phylogenetic analyses have supported the inclusion of three genera in the Psoraceae, Psora, Protoblastenia and Brianaria (Ekman & Svensson 2014). The last genus was only described recently to include a group of species previously included in a different genus Micarea belonging to an entirely different lichen family, the Pilocarpaceae. Micarea lichens closely resemble Brianaria species in overall appearance but differ in some features including the nature of their algal symbiont. Past authors often assumed that symbiont associations provided little guidance to lichen relationships; it was thought that a germinating lichen fungus would pretty much form a connection with whatever algal species was available. However, more recent investigations have found that the tastes of lichen fungi are more discriminating. Micarea species form associations with small algal cells, four to seven microns in diameter, with thin cell walls that are often found in pairs within the lichen thallus. Brianaria species, in contrast, have larger algal symbionts that are always isolated in the thallus (Andersen & Ekman 2005).


Andersen, H. L., & S. Ekman. 2005. Disintegration of the Micareaceae (lichenized Ascomycota): a molecular phylogeny based on mitochondrial rDNA sequences. Mycological Research 109 (1): 21–30.

Ekman, S., & R. Blaalid. 2011. The devil in the details: interactions between the branch-length prior and likelihood model affect node support and branch lengths in the phylogeny of the Psoraceae. Systematic Biology 60 (4): 541–561.

Ekman, S., & M. Svensson. 2014. Brianaria (Psoraceae), a new genus to accomodate the Micarea sylvicola group. Lichenologist 46 (3): 285–294.

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