ASCOMYCOTA | LECANOROMYCETES > LECANORALES > Lecanoracea

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

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

Synonym:                    -          

Primary habitat:            Woodland, wayside trees, fences and posts

Usual substrata:            Bark, or worked wood

Growth form:                Corticolous, lignicolous

Thallus:                  Crustose

Apothecia:                    Lecanorine

BLS identity rating:        Graded 2/5 (visual identification possible with care)

Thallus variable, but roughly circular, usually forming neat delimited patches from 3-12cm across; relatively thick, smooth to roughened or slightly warty, sometimes areolate; typically, pale grey, although sometimes creamy to yellow-grey, turning green when wet; prothallus white, but not always conspicuous with some authors describing as absent.

Apothecia numerous, often tightly packed, at least in part; up to about 1mm dia., occasionally a little larger; disc colour variable, effectively two morphs; the lighter of which ranges from dull brown to rose-brown or orange brown; the darker, red- brown or chestnut-brown; only rarely slightly pruinose; persistent and well-developed, smooth or slightly crenulate, occasionally distorted when grouped; thalline margin near enough concolourous with the thallus; clusters of angular crystals, not dissolving in K, are present around the margin, and on top of the epithecium there's a dense layer of fine granules, which will dissolve in K.

It has been observed that the form with paler coloured discs generally has an off-white thallus, whereas the one with darker, typically chestnut-coloured discs, tend to have a purer white thallus.

Lecanora chlarotera is a widespread species occurring on trees, as well as fences and other worked timber, mostly in non- polluted areas. It was once regarded as very common, but it is now considered to have been much confused in the past with Lecanora hybocarpa, particularly in the south, also in mature woodlands with Lecanora argentata. All three species are part of the Lecanora subfusca group, together with Lecanora pulicaris and Lecanora sinuosa. There are others, but these are the five corticolous Lecanora species that generally need to be considered and distinguished.

Lecanora chlarotera will most likely be found on deciduous trees either in woodland or alongside paths and tracks in more exposed locations. Both colour morphs can occur on trunks but, on branches and twigs, it is more likely to be the darker form.

Although chemical reactions and close examination of apothecial crystals are necessary to be sure, there are some good visual indicators which, together with information regarding habitat, tree type and likely location on the tree, provide sufficient detail to determine the most likely species. In that respect, I'm saying that whilst the descriptions here are accurate, the associated photos are only representative - hopefully.