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Images of British Lichens

Cladonia arbuscula (Wallr.) Flot.
subsp. squarrosa (Wallr.) Ruoss

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 when fresh.

[Subspecies arbuscula has shorter, more crowded branches, Pd yellow, rare. The separation of subspp. squarrosa and arbuscula seems to work with British material, with correlation of Pd test, morphology and ecology, but is probably untenable on a wider scale and the separation is not accepted by Ahti & Stenroos in Nordic Lichen Flora (2013). C. mitis has shorter, often less curved branches, which are often less unidirectional, brown only at the very tips, Pd negative (uncertainly always so), rare. C. ciliata has 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); Nordic Lichen Flora (2013) 5: 18, 94 (as species, subspp. not given separate recognition, 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, 2013), 124-125 (as Cladina arbuscula, photo [James in Smith et al. considers this C. mitis, but it does look more like weak arbuscula]); Aptroot et al. (2011), 46-7 (photos, apparently this subspecies); Wirth (1995), 1: 294 (photo, apparently this subspecies), 296; Wirth et al. (2004), 71 (photo, apparently this subspecies); Wirth, Hauck & Schulz (2013), 1: 10 & 390 (photos, apparently this subspecies), 374; Holien & Tønsberg (2008), 81 (as species, photo); Stenroos et al. (2011), 116-7 (photo, as this subspecies); 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).


Cladonia arbuscula subsp. squarrosa
In montane heath, the Lecht, Aberdeenshire, August 2009
Cladonia arbuscula subsp. squarrosa
In upland heath, Grantown-on-Spey, Morayshire, July 2008
Cladonia arbuscula subsp. squarrosa
Cladonia arbuscula subsp. squarrosa
In dune heath, Cuthill Links, East Sutherland, July 2008
Cladonia arbuscula subsp. squarrosa
In dune heath, Cuthill Links, East Sutherland, April 2009

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© A.J. Silverside
Uploaded August 2010, last updated January 2016