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Xanthoria polycarpa (Hoffm.) Th.Fr. ex Rieber


Foliose, thallus greenish grey (shade) to orange-yellow, with ascending to adpressed lobes, subdivided into few to many short, irregular, finger-like sub-lobes less than 1mm in width, margins irregularly nodulose but isidia and soredia absent; apothecia usually abundant, held above and often hiding the thallus, margins concolorous with thallus, discs deep yellow to dark orange. Widespread on nutrient-enriched trees, especially on small twigs where it forms clusters of apothecia in axils of branches; becoming common as an indicator of nitrogen deposition.

Refs: Smith et al. (2009), 971; Purvis et al. (1992), 647; Dobson (2005), 464; Dobson (2011), 473 (photo); Whelan (2011), 151 (photo); van Haluwyn et al. (2009), 32-3 (photo); van Herk & Aptroot (2004, 2013), 398-9 (photo); Wirth (1995), 2: 973, 977 (photo); Wirth et al. (2004), 128 (photo); Wirth, Hauck & Schulz (2013), 2: xx (photo); Wirth, Hauck & Schulz (2013), 2: 720 (photo, as Massjukiella polycarpa), 1192; Frahm et al. (2010), 152 (photo); Moberg & Holmåson (1984), 190 (photo); Holien & Tønsberg (2008), 105 (photo); Stenroos et al. (2011), 40 & 507 (photos); Puntillo (1996), plate 42 (photo); Hinds & Hinds (2007), 525 (photo); Brodo et al. (2001), 746-7 (photo); McCune & Geiser (2009), 398 (photo).

An often distinctive species but mimicked on small twigs by young thalli of X. parietina, which cannot be separated by measurements of thallus diameter or lobe width.

 
Xanthoria polycarpa
On Oak (Quercus robur), Wicken Fen, Cambridgeshire, April 2005


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Uploaded August 2008, last updated December 2013