Cladonia arbuscula
Thallus: primary thallus crustose, evanescent. Podetia 40-100 mm tall, yellow-green to yellowish grey, paler at the bases which frequently become necrotic; main axis distinct, often robust, 1.1.5 mm diam.; surface ± uneven-roughened, ecorticate but only inconspicuously felty, the algae held in small, hardly protruding and often elongate areoles, soredia absent; fairly richly to richly branched, terminal branches notably recurved and markedly orientated in one direction, branching predominantly trichotomous or tetrachotomous at apices; young apices <2 mm diam., blunt.
Anamorph: conidiomata pycnidia, frequent, ± cylindrical to ovoid, the contents colourless.
Teleomorph: ascomata apothecia, rather rare, when present in clusters at branch tips, 0.5-1mm diam., ± spherical, brown, inconspicuous.
Chemistry: thallus C–, K–, KC+ yellow, Pd+ rust-red, rarely yellow, UV– (psoromic or fumarprotocetraric and usnic acids).
In GB&I, Cladonia arbuscula has been separated into subspp. arbuscula and squarrosa; the latter was considered to be more common and the dominant European subspecies, and was separated from subsp. arbuscula primarily by a Pd+ rust-red rather than yellow reaction. Recent molecular data suggests that the distinction between the two subspecies is blurred, and they are not separated in this account.
Cladonia arbuscula subsp. arbuscula is considered to be Data Deficient by Woods & Coppins (2012), and has been designated as Nationally Rare and is cited in the NC(Scotland) Act 2004. C. arbuscula subsp. squarrosa was considered as of Least Concern, so the species as a whole should be placed in that category.
Characterized by the richly branched, yellow-green podetia with recurved branchlets with tri- and tetrachotomous endings. The similarly coloured C. portentosa has terminal branchlets which are not recurved and diverge in all directions forming broccoli-like tufts; C. ciliata var. tenuis differs in the dichotomous branching, more slender, strongly recurved, orientated branchlets.
The species is distinctive for its markedly asymmetrical branch tips that are recurved in the same direction. It could be confused with Cladonia rangiferina, which has a similar overall appearance but with corticate, smooth-walled podetia and is usually Pd- and K+ yellow. Its relatively robust and upright habit distinguishes C. arbuscula from the prostrate, sprawling C. mediterranea. C. mitis has been shown to be closely related to C. arbuscula (see Phylogeny), but is usually Pd- and has more lax and more weakly oriented branches.
Cladonia mitis forms a well-defined clade according to multigene phylogenetic analysis, but there are indications that it nests within a paraphyletic C. arbuscula.
In GB&I, scattered throughout the British Isles but rare in C and E England where habitat loss and eutrophication has led to its decline.
Montane and lowland heathlands and acid dunes; on nutrient-poor and often ± boggy soils.