ASCOMYCOTA | LECANOROMYCETES > LECANORALES > Lecanoracea

Genus Lecanora, meaning 'beautiful small bowl' - from the shape of the apothecia

Common name:            Members of the genus collectively known as 'rim lichens'

Synonym:                    Lecanora subfuscata

Primary habitat:            Mature woodland  

Usual substrata:            Bark  

Growth forms:              Corticolous  

Thallus:                  Crustose

Apothecia:                    Lecanorine

BLS identity rating:        Graded 2/5 (relatively straightforward, but microscopic examination needed to be sure)

Thallus typically with a 3-10cm spread; generally uneven and warted centrally, but with smoother margins; usually, at least in part, surrounded by a relatively well-defined black prothallus; creamy or greyish-yellow to greenish white.

Apothecia scattered or aggregated, not particularly numerous; up to about 1mm dia; discs typically reddish-brown, sometimes piebald, flat or slightly convex; thalline margin persistent, smooth to strongly crenulate, near enough concolourous with the thallus; contains large crystals not soluble in K; epithecium without granules; hymenium sometimes lacking, leaving an empty, somewhat glossy, bowl; pruinose absent.

Confirmed distribution records of Lecanora argentata are rather sparse due to some confusion with L.chlarotera and the need for microscopic examination, coupled with using polarised light microscopy, in order to ensure identification is correct. It is now suspected that many old records of L.chlarotera in mature woodland locations were probably L.argentata. Those records that have been verified are rather well scattered across the UK with no clear pattern other than the species is clearly more frequent in certain western areas.

The main visual differences between the two species are that L.chlarotera has a continuously smooth thallus without a dark surround, and very variably coloured apothecia. L.argentata has a centrally rough thallus that becomes smooth around the margins where it is normally limited by a dark prothallus, and has far more consistently coloured apothecia.

Lecanora argentata is usually found on the trunk, rather than branches or twigs, of older, smooth-barked, deciduous trees, notably Ash, in mature woodland areas.