Images of British Lichens
Lecidea grisella Flörke
Thallus continuous, smooth, becoming rimose or cracked-areolate, whitish-grey to pale grey-brown crust, cortical surface testing strongly red with bleach (sodium hypochlorite); apothecia immersed, flat to slightly convex, grey-pruinose to black. Widespread and common on siliceous but nutrient-enriched rocks and stonework (as when mortar has been used with base-poor rocks or birds perch on them).
Refs: Smith et al. (2009), 511; Dobson (2005), 235-6 (photo, as L. fuscoatra); Dobson (2011), 239-40 (photo); Wirth, Hauck & Schulz (2013), 1: 643, 653 (photo); Valcárcel et al. (2003), 224-5 (photo, as L. fuscoatra var. ).
An old 'split' of Lecidea fuscoatra, revived at species level by Aptroot et al. in Smith et al. (2009). True L. fuscoatra (page pending) is areolate from the start, sometimes with more convex areoles and is more often brownish. Wirth (1995), 1: 513, gives a good photograph. L. grisella is the more common and widespread of the two.
Lecanora rupicola, when its apothecia are parasitised by Arthonia varians, can resemble this species closely but lacks the red reaction with bleach.
Lecidea is, obviously, part of the very large 'Lecidea group' of lichens – crustose species with dark or black apothecia that lack distinct 'thalline' margins, though they will usually have differentiated 'proper' margins the same colour as the disk. Microscopic examination of mature apothecia (and sadly they are often not mature) is usually necessary even to be sure of the genus, and field identification of all but a few distinctive species is risky. Dobson (2011), pp. 236-7, gives an invaluable analysis of the component genera.
|On siliceous, montane rocks, Beinn Airein, Isle of Muck, July 2012 (BLS meeting), showing C+ red reaction|
|Material with apothecia, on urban, sandstone stonework, Paisley, Renfrewshire, June 2011|
|On old stone wall-top, Kindrogan, Perthshire, March 2008|
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© A.J. Silverside
Uploaded October 2008 (as Lecidea fuscoatra), updated and renamed June 2009, last updated September 2013