Images of British Lichens
Porpidia speirea (Ach.) Kremp.
A crustose, 'lecideine' lichen with a white to grey, often chalky thallus, lacking soredia; apothecia black, pruinose when young, initially sunk in thallus surface, thallus cracking around the apothecia but leaving a narrow rim to each apothecium. Upland areas of the north and west, on limestones, schists and other base-rich rocks.
Refs: Smith et al. (2009), 747; Purvis et al. (1992), 499; Dobson (2005), 362 (photo); Dobson (2011), 365-6 (photo); Wirth (1995), 2: 766; Wirth, Hauck & Schulz (2013), 1: 635 (photo, as Lecidea speirea), 642, 2: 921; Thomson (1997), 496, 497 (photo).
Porpidia is part of the very large 'Lecidea group' of lichens – crustose species with dark or black apothecia which 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. 236-237, gives an invaluable analysis of the component genera.
|On limestone outcrop, Braemar, Aberdeenshire, April 2003|
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Uploaded July 2008, last updated September 2013