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Buellia aethalea (Ach.) Th.Fr.


Thallus crustose, areolate, variable, light to dark grey to grey-brown, bounded by a black prothallus, which is often also visible between the areoles, and which on open surfaces is often conspicuously fimbriate at the margins, thallus normally testing yellow, slowly turning red, with potassium hydroxide, non-reactive with bleach, sodium hypochlorite; apothecia black, lecideine, variable in shape, set down in the areoles (innate), with margins thin and usually inconspicuous but sometimes with a "collar" of thallus material, ascospores brown, 1-septate. Widespread and common, but often as small thalli within lichen mosaics and easily overlooked, on nutrient-poor rocks including quartzite, also an early colonist of made-made substrates such as glass and paintwork.

Refs: Bungartz et al. (2007), 127, (also photo in photographic section); Smith et al. (2009), 231; Purvis et al. (1992), 131; Dobson (2005), 87 (photo); Dobson (2011), 95 (photo); Whelan (2011), 55 (photo); van Herk & Aptroot (2004, 2013), 82-3 (photo); Nordic Lichen Flora (2002) 2: 13, 90 (photo); Valcárcel et al. (2003), 130-1 (photo).

A small and not always easily recognised species, most readily confused with other Buellia species but also with the equally common Rhizocarpon reductum (page pending), which has somewhat larger thalli, apothecia with thicker proper margins, is generally K+ yellow (but may be K+ red), and which can also have a markedly fimbriate prothallus when an early colonist. Examination of the ascospores may be necessary (1-septate in B. aethalea, multiply septate in two directions, i.e. muriform, in R. reductum). It may take a while to understand B. aethalea and a higher than usual proportion of internet photographs strike me as doubtful.

FGBI: http://fungi.myspecies.info/all-fungi/buellia-aethalea

Buellia aethalea on gravestone
Buellia aethalea on gravestone
Buellia aethalea on gravestone
On quartzite gravestone, Kirkton of Collace, Perthshire, September 2012
 
Buellia aethalea on gas tank
Buellia aethalea on gas tank
Pioneer stages (largely prothallus but some mature spores found), on painted surface of old propane gas tank, Orielton, Pembrokeshire, May 2009


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© A.J. Silverside
Uploaded April 2013, updated January 2016