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Porpidia crustulata (Ach.) Hertel & Knoph


A crustose, 'lecideine' lichen with a thin or very thin, effuse, white or cream to grey thallus, occasionally tinged orange, lacking soredia; apothecia black, sometimes thinly pruinose when young but usually rather shiny, frequently clustered or in concentric rings. Widespread and often common on base-poor rocks. Although only rarely tinged with orange, this species will not key out in 'Purvis' without such colouration!

Refs: Smith et al. (2009), 743; Purvis et al. (1992), 496 only, not key; Dobson (2005), 360 (photo); Dobson (2011), 363 (photo); Whelan (2011), 133 (photo); Wirth (1995), 2: 768 (photo); Wirth et al. (2004), 199 (photo); Wirth, Hauck & Schulz (2013), 2: 923 (photo); Valcárcel et al. (2003), 322-3 (photo); Brodo et al. (2001), 584-5 (photo); Walewski (2007), 65 (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.

 
Porpidia crustulata
Porpidia crustulata, closer view
Braemar, Aberdeenshire, March 2008


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Uploaded February 2009, last updated September 2013