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Parmelia saxatilis (L.) Ach.


Thallus foliose, pale green to grey, sometimes browning at drying lobe tips, with conspicuous, white pseudocyphellae on the lobe surfaces and becoming densely isidiate on older parts of the thallus, the isidia shining, or often pruinose, arising initially from the pseudocyphellae and arranged in a net-like pattern; apothecia frequent, with orange-brown discs and isidiate margins. Widespread and locally common on base-poor rocks and frequent on acid-barked trees and on trees where the bark has been acidified by atmospheric pollution.

Refs: Smith et al. (2009), 653; Purvis et al. (1992), 425; Dobson (2005), 302-303 (photo); Dobson (2011), 305 (photo); Jahns (1983), 198-9 (photo); Allen (2007), 24 & 38 (photos); Whelan (2011), 121 (photo); van Haluwyn et al. (2009), 56-7 (photos); van Herk & Aptroot (2004, 2013), 276-277 (photo); Hansen & Anderson (1995), 46 (photo); Wirth (1995), 2: 646, 663 (photo); Wirth et al. (2004), 96 (photo); Wirth, Hauck & Schulz (2013), 2: 803 (photo), 807; Frahm et al. (2010), 120 (photo); Moberg & Holmåson (1984), 94 (photo); Holien & Tønsberg (2008), 56 (photo); Nordic Lichen Flora (2011) 4: 87, 162 (photo); Stenroos et al. (2011), 304-5 (photo); Valcárcel et al. (2003), 278-9 (photo); Puntillo (1996), plate 29 (photo); Pope (2005), 34 (photo); Brodo et al. (2001), 483 (photo); Hinds & Hinds (2007), 338-9 (photo); McCune & Geiser (2009), 223 (photo); Lichen Atlas of the British Isles 1: 1015 (1995).

The recently recognised P. ernstiae (page pending) occurs on nutrient-rich bark of trees such as Ash and differs principally in its at least partly pruinose upper surface, along with abundant production of small lobules (most noticeable in Spring) and isidia more randomly arranged on the younger thallus lobes.

Lichenicolous fungi on P. saxatilis include Homostegia piggotii, Marchandiomyces corallinus and Nesolechia oxyspora.

 
Parmelia saxatilis
Parmelia saxatilis
On sandstone wall, Stanhope, Co. Durham, June 2009
 
Parmelia saxatilis
Parmelia saxatilis, apothecia
On siliceous rocks, Mar Estate, Aberdeenshire, April 2008
 
Parmelia saxatilis
Parmelia saxatilis, close view showing isidia
On drystone wall, Kilmacolm, Renfrewshire, March 2010
 
Parmelia saxatilis, with apothecia
On siliceous rocks, Braemar, Aberdeenshire, April 2002
 
Parmelia saxatilis, isidia
Isidia on older part of lobe surface, material from drystone wall, Moulin, Perthshire, April 2008
 
Parmelia saxatilis, showing oribatid mite damage
Parmelia saxatilis, showing oribatid mite damage
Material showing extensive oribatid mite grazing damage and discolouration, on drystone wall, Glennifer Braes, Renfrewshire, October 2011


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© A.J. Silverside
Uploaded April 2008, last updated February 2014 (first hosted at www-biol.paisley.ac.uk, January 2003)