Collema
Mostly foliose lichens containing cyanobacteria (Nostoc); thallus foliose, squamulose, or rarely crustose-areolate, often isidiate, black, dark brown or olive-brown, lacking a cellular cortex, surfaced instead by a textured gelatinous layer; apothecia with an algal rim that generally has a cellular cortex, generally also with a distinct inner, non-algal layer of rounded or blocky cells; hymenium light orangish brown in upper portions, formed of straight, unbranched paraphyses embedded in thick gel; hypothecium colourless; asci with a distinctly thickened tholus containing a dark blue ring structure; spores 2-16 per ascus, mostly 8, colourless or somewhat brownish, always septate, often with both longitudinal and transverse septae, bacilliform, elliptical, fusiform, subglobose or oblate.
References: Purvis et al. 1992; Degelius 1954.
Collema aphanes Björk & Goward ined.
Thallus granular, greasy and blackish olive-brown when wet, slightly glossy and olive-brown when dry, containing Nostoc; thallus interior formed of blocky cells tightly packed; upper and lower surfaces formed of a pseudocortex tissue (cells tightly packed, but poorly distinguished from the cells of the thallus interior); apothecia with a thick, prominent thalline rim; disc and rim level, coloured like the thallus; spores 9-17 × 6.5-8 µ, broadly oblong to rounded rectangular, thin-walled; conidia 4-5 × 1.2 µ.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: on nutrient-rich bark in humid sites in lower elevation forest.
Similar Species: Leptogium cellulosum and other diminutive Leptogium species may appear similar, but have a eucortex formed of cells that are clearly distinguished from the cells of the thallus interior (blockier and thicker walled).
Specimens: Björk 9894, 12878; Goward 02-36.
Local Status: Occasional.