Parmeliopsis ambigua
Thallus yellow-grey to greenish, to about 40 mm diam. Lobes flat, closely appressed, to 1 mm diam and frequently palmately divided. The lobe tips have discrete soralia and they and the centre of the thallus become covered with concolorous powdery soredia. Lower surface black in the centre with simple stout rhizines that adhere firmly to the substratum, becoming light brown towards the lobe tips and lacking rhizines.
Anamorph: no information available.
Teleomorph:Ascomata very rare in Britain, with light brown discs. Ascospores 7-11 x 2-3 µm.
Chemistry: cortex K+ very pale yellow, KC ± yellow. Medulla UV+ white.
Assessed by Woods & Coppins (2012) as of Least Concern.
This species was increasing due to the spread of acid rain, but with present lower levels of pollution is declining rapidly, especially in the South
The similar Parmelia mougeotii is P+ orange, K+ yellow and has more convex and shiny lobes with coarser soralia.
Common in central and eastern Scotland and northern England, extending southwards but there less frequent. BLS map here.
Common on coniferous trees and wood, also on air-polluted acidified bark of deciduous trees, occasionally on worked timber.