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General:
Common Name: The Brownette Lichens. Stresses the miniature size and superficial resemblance to certain species of “brown” lichens (e.g., Melanelia and Neofuscelia).
Minute to small stratified to nonstratified foliose or occasionally squamulose lichens, corticate above and below, isidiate or not, lobes closely appressed or partly semi-erect, elongate-linear, linear or occasionally short, averaging to (0.1–) 0.2–0.8 (–l.5) mm wide, thin. Upper surface dark olive-brown or blackish, smooth or longitudinally striate. Lower surface dark or occasionally pale, bearing blue-green or occasionally pale rhizines, these often extending outward from thallus as prothallus. Medulla white. Photobiont blue-green.
Apothecia located over upper surface, disc dark brown to black; spores 2- to 4-celled, ellipsoid to somewhat spindle-shaped/fusiform, colourless, (4-) 8 per ascus.
Over rock, rarely over bark.
Notes: Placynthium is primarily a temperate genus, consisting of approximately 25 species worldwide. Of the six species occurring in North America, five are reported from B.C. In this taxonomically rather difficult genus, conclusive identification of some species requires detailed anatomical studies (see Henssen 1963d). No lichen substances have been reported.
Species description:
Thallus broadly or narrowly attached to substrate, but not umbilicateAND
Thallus brownish; lobes not at all swollen; substrate variousAND
Lobes either mostly appressed to substate or, if erect, then over rock AND
Lower surface and rhizines blue-green or blackish AND
Peripheral lobes scalelike/isodiametric and strongly disjointed, usually bordered by distinct, darkened hypothallus which also usually borders the thallus as a whole
Comments:
Only var. nigrum has been recorded from B.C., though var. tantaleum (Hepp) Arnold is known to occur in Jasper National Park and may yet be found west of the continental divide. 1. var. nigrum - Spores 2-, 3- or 4-celled, narrow–ellipsoid, 3.5–5.5 micrometres wide.
2. var. tantaleum (Hepp) Arn - Spores 1- or 2-celled, broad–ellipsoid, 6–8 micrometres wide
Source: Lichens of British Columbia |
