Images of British Lichens
Buellia stellulata (Taylor) Mudd
Thallus crustose, cracked-areolate (frequently described as 'rimose' but see below), pallid whitish, usually bounded by a black prothallus which is also visible between the areoles, thallus testing yellow (not turning red) with potassium hydroxide (K+), non-reactive with bleach, sodium hypochlorite (C-); apothecia black, lecideine, initially set down in and between the areoles (innate) but becoming slightly raised, with margins often greyish from remains of necrotic thalline material (Bungartz et al., 2007), ascospores brown, 1-septate. A colonist on nutrient-poor rocks and shingle, distribution predominantly western and coastal, apparently over-recorded elsewhere for B. aethalea.
Refs: Bungartz et al. (2007), 168; Smith et al. (2009), 237; Purvis et al. (1992), 136; Dobson (2005), 90; Dobson (2011), 98 (photo); Valcárcel et al. (2003), 134-5 (photo); Nordic Lichen Flora (2002) 2: 22, 94 (photo).
The small size of these Buellia species of the 'aethalea-group' is a photographic challenge and the genus tends to be under-represented in lichen books and on websites. While checking details for this webpage I have nevertheless noted some discrepancies. To my mind this species is areolate, but described by some authors as 'rimose'. Further, while the lichen shown here matches British/Irish concepts (and was initially pointed out and determined by David Hawksworth), there are photographs on reputable, mainly continental websites that show a lichen with a relatively smooth, cracking (i.e. rimose!) thallus, with sessile (apparently not immersed), more uniformly rounded apothecia. It may be that the species name is being applied to more than one species.
If so, it should be noted that the species name is defined by the description by Thomas Taylor in his account of Irish lichens in vol. 2 of J.T. Mackay's Flora Hibernica (1836), page 118. It is worth reproducing part of his description (as Lecidea stellulata) here:
"Substratum of the thallus very thin, black, exceeding at the edges; the upper layer of minute, brilliant, smooth, tartareous, roundish, subcrenate scales, aggregated in a subradiated manner"
This would appear to confirm that the current British/Irish concept, also that illustrated in the Nordic Lichen Flora and covered by the detailed description of the species by Bungartz et al., is the correct one.
|On gravestone, Slapton, South Devon, August 2011|
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Uploaded April 2013, updated January 2016