Cladonia arbuscula subsp. squarrosa (images of British lichens)

One of the 'reindeer lichens' (subgenus Cladina), podetia sprawling to erect, in tufted mats, cream to pale greyish green when fresh, with patches of algal cells set in the cortex, greyish white when dry, ultimate branches brown, branches ± straight to recurved, all in one direction, ultimate branches generally in fours (tetrachotomous); pycnidia small, brown, containing colourless jelly, located on the branch tips, apothecia small, brown, rare. Generally in exposed heathland, on bog surfaces and on base-poor dunes, very often mixed with other members of subgenus Cladina, widespread in suitable habitats but generally more common in the north and west. Generally recognisable in the field but needs laboratory confirmation; Pd (para-phenylenediamine) test rapidly orange-red, UV-. (All photographs shown here are of Pd-tested material.)
On wet bog surfaces the podetia can become black below; such examples must not be confused with the rare C. stygia, noted for this character but also with more "woolly" (densely tomentose-downy) podetia and red pycnidial jelly.

[Subspecies arbuscula has shorter, more crowded branches, Pd yellow, rare; C. mitis with shorter, often less curved branches, often less unidirectional, brown only at the very tips, Pd negative (uncertainly always so), rare; C. ciliata with finer branches, branching dichotomous but often with successive dichotomies seeming tetrachotomous, Pd rapidly deep orange-red. All testing must beware of mixed species within single clumps.]

Refs: Smith et al. (2009), 317; Purvis et al. (1992), 195 (as species); Ahti (1961), 101-108 (as subsp. arbuscula, "chemical strain I"), plate 38 (photo); Dobson (2005), 132 (photo); Dobson (2011), 140, 141 (photo); Britton (2008) 23 (photos); Jahns (1983), 212-213 (as species, photo); van Herk & Aptroot (2004), 124-125 (as species, photo [James in Smith et al. considers this C. mitis, but it does look like weak arbuscula]); Wirth (1995), 1: 294 (photo, apparently this subspecies), 296; Wirth et al. (2004), 71 (photo, apparently this subspecies); Holien & Tønsberg (2008), 81 (as species, photo); Hansen & Andersen (1995), 23 (as Cladina arbuscula, photo); Thomson (1967), 150, plate 25 (as C. sylvatica, photo); Hinds & Hinds (2007), 163 (photo), 164; Lichen Atlas of the British Isles 2: 360 (1996).

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Images of British Lichens