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Cladonia thomsonii Ahti
Family: Cladoniaceae
Cladonia thomsonii image
Lucy Taylor  
Thompson, J., 1984. American Arctic Lichens: The Macrolichens.
Primary thallus unknown. Podetia growing in dense to loose cushions, dying at the base, usually 4-6 cm tall, the branches ashy white, 1-3 mm thick, with irregular anisotomic polytomy with tetrachotomy dominant but dichotomy frequent; cupless or with indistinct cups at the axils, the axils usually perforate; the podetial wall also may become split with age, podetial squamulus rare, scarcely lobate, 1-3 mm long; podetial surface areolate corticate with rather wide white, arachnoid medullary interspaces; the base sometimes with tuberculate outgrowths, becoming yellowish gray to black. The podetial wall 220-300 μ thick with 25-40 μ cortex, the inner cartilaginous layer 50-75 μ, the inner surface slightly longitudinally furrowed, somewhat glossy and with scattered, minute papillae. Apothecia brown, the margins persistent, spores not seen. Pycnidia at tips of podetia, containing hyaline jelly, the conidia 6 x 1 μ.

Reactions: K+ yellow, C— , KC— , P—.

Contents: atranorin usually with one or two of three unknowns in TLC tests, differing from C. wainii Sav. in that the latter Siberian species contains the atranorin plus two different unknowns.

This species grows on gravelly tundras and well-drained alpine tundras. It is so far known only from Alaska and the Northwest Territories near the mouth of the Mackenzie River. It is probably closely related to the poorly known C. wainii Sav., which is reported only from the type locality in Kamchatka. It differs in being whitish rather than grayish, with narrowly isotomic instead of widely anisotomic branching, and with one dark brown spot at Rf 0.43 instead of two purple-brown spots at Rf 0.5 and 0.47 in n-hexane-ether-formic acid, 5:4:1. Yoshimura (1968) suggested that it might be a new species and Krog (1968) and Ahti (1973) agreed and so described it in 1978b.