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General:
Common Name: The Tarpaper Lichens. Stresses the blackish nonstratified medulla that becomes somewhat swollen, translucent and jellylike when moistened.
Minute to occasionally large nonstratified foliose lichens (gelatinous when wet), lacking true cortex, (except cortex present on apothecial margin: see below) isidiate or not, lobes closely appressed to semi-erect, 0.5–10 (–15) mm wide, thin to thick. Upper surface dark olive brownish or blackish (ours), dull. Lower surface dark, rhizines absent or rarely present. Medulla absent. Photobiont blue-green.
Apothecia located over upper surface or marginal, with thalline margin, disc reddish brown; spores 2- to multicelled, ellipsoid to needle-shaped/acicular, (4–) 8 per ascus. Over bark, earth and rock, usually base-rich.
Notes: Collema is a taxonomically difficult genus comprising about 80 species, of which 35 are known to occur in North America and 20 in B.C. Chemistry is of no diagnostic value in this genus. Two keys are provided. The first key emphasizes macroscopic vegetative characters, though spore characters have been incorporated in some places. The second key, to nonisidiate species, stresses spore characters and is more technical.
Species description:
Lobe margins hairless; isidia, if present, also lacking hairs AND
Thallus foliose or, if somewhat fruticose, then lobes proportionally much shorter and broader; habitat and distribution various AND
Lobes brownish to olive-brownish or blackish, but never jet black above and below; rarely pruinose; habit, substrate and distribution various AND
Isidia present, these mostly flattened and scalelike at maturity; scalelike lobules therefore rather common over upper surface AND
Lobes averaging to less than 4 (–5) mm wide; lobe margins often undulate
Comments:
Only var. crispum is reported from B.C. The material seems to be heterogeneous and includes a soildwelling taxon in which the lobe tips are distinctly swollen and the “isidia” soon become erect. This material should perhaps be referred to the C. tenax group.
Source: Lichens of British Columbia |
