Alectoria ochroleuca
Thallus to 8(-12) cm, erect or becoming sprawling; branching moderate, ± anisotomic-dichotomous; branches 0.5-2 mm diam., the main stems terete, never strongly compressed, yellowish green to bright yellow, the apices often black or greenish black, ± matt. Pseudocyphellae ca 1 × 0.1 mm, abundant, elliptical, white.
Anamorph: pycnidia frequent, to 150 μm diam., ± apical, black.
Teleomorph: apothecia unknown in the British Isles.
Chemistry: medulla C–, CK+ yellow, K–, KC–, Pd–, UV– (diffractaic acid); cortex KC+ pale yellow (usnic acid).
Assessed as Vulnerable by Woods & Coppins (2012). It is considered to be Nationally Rare, is a UK BAP Priority Species on Schedule 8 of the Wildlife & Countryside Act 1981 and in Section 2(4) of the Nature Conservation (Scotland) Act 2004. It was described as rare and decreasing by Gilbert & Purvis (2009), and is potentially vulnerable to climate change due to it being confined to high-montane habitats.
Sometimes confused with Alectoria sarmentosa subsp. vexillifera, which is prostrate, has compressed and ± flattened main stems, and a UV+ ice-blue medulla reacting usually KC+ red but never CK+ yellow. Some pale morphs of A. nigricans can also look similar to A. ochroleuca, but that species does not have a yellowish tinge to the thallus and its cortex and medulla is C+ red.
In GB&I, restricted to the Cairngorm range, but with a broad bipolar arctic-alpine distribution on a global level.
On the ground or among dwarf shrubs in Racomitrium - Empetrum communities, above about 800 m altitude.