Thallus prostrate or decumbent, straggling, occasionally ± densely tufted, to ca 50 mm in length and 1-2 mm diam., not or sparingly branched, the branches chalk-white, hollow, cylindrical, smooth, worm-like, the apices pointed, the base usually dying with the thalline units becoming vagrant. Cortex composed of longitudinally orientated hyphae. Medulla thin, also of longitudinally orientated hyphae. Soredia and isidia absent. Photobiont trebouxioid.
Anamorph: conidiomata formed as small pustules on the thallus surface, 200–350 µm diam. and 150–200 µm tall, ± hemispherical, the surface irregular, ostiolate, with pinkish exudates formed by a mucilaginous mass of conidia. Conidiophores elongate, forming chains of intercalary conidiogenous cells with peg-like processes near the upper cell septum. Conidia 3-5 x 1-2 µm, bacilliform, tapering slightly at one end, hyaline aseptate, thin-walled.
Teleomorph: not known.
Chemistry: thallus C–, K+ pale yellow, KC–, Pd+ yellow, UV+ white (baeomycesic and squamatic acids).
Assessed by Woods & Coppins (2012) as of Least Concern, though more or less confined to high mountains and the extreme north and thus vulnerable to climate warming.
GBI collections have been assigned to Thamnolia vermicularis var. subuliformis. This has been distinguished from the type variety by its UV+ white, K+ pale yellow and Pd+ yellow reactions, versus UV-, K+ bright yellow and Pd+ orange to red for var. vermicularis. Recent phylogenetic research has shown that chemistry does not appear to be a good differential feature for infraspecific groupings within the species as a whole. The chalk-white, worm-like, usually unbranched, hollow and prostrate thalli are unlikely to be confused with any other species; Siphula ceratites shows some similarities but has a shorter, erect, compact thallus.
Locally frequent in montane areas of NW England (Lake District), N Wales and the Scottish Highlands. BLS map here.
On exposed montane heaths, often amongst Rhacomitrium lanuginosum and Salix herbacea above 850 m, rarely at sea-level on heaths developed on old shingle ridges and dunes in N Scotland