Haematomma
A genus of crust lichens containing trebouxioid algae; thallus smooth to areolate, verruculose, granular, or sorediate, white, grey or creamy yellowish; apothecia with an algal rim that is like the thallus in colour and texture, and with a deep red or red-orange disc; margin with a spongy medulla that gives it an opaque appearance; hymenium of gel--embedded, densely branched and anastomosing paraphyses, infused with anthraquinone crystals; hypothecium colourless or pale; asci clavate, thin-walled but with a modestly thickened tholus that reacts IKI+ blue with an ocular chamber and pale axial mass; spores 4-8 per ascus, colourless, narrowly fusiform to acicular, with at least 3 transverse septae.
References: Brodo et al. 2008.
Haematomma ochroleucum (Necker) J.R. Laundon
Thallus diffusely sorediate to leprose, corticate portions lacking, yellowish or pale bluish green, conspicuously outlined by a wide, cottony, pure white prothallus; soredia conglutinated into tight clusters 25-125 (‑250) µ; apothecia rare, with a blood-red disc that reacts K+ violet; spores with 3-7 widthwise septae, 30-70 × 5-7 µ; mostly on rock in cool, humid places, less common on bark.
Reactions: K+ yellow, C-, KC- or + yellow-orange, PD- or + pale yellow.
Contents: Atranorin, porphyrilic acid, zeorin, and with or without usnic acid.
Habitat: Usually on rock, but also on rough bark of Populus trichocarpa. Lower elevations.
Similar Species: easily confused with Phlyctis argena, the thallus of which is K+ yellow turning red.
Specimens: Björk 9523, 12475.
Local Status: Uncommon.