Mycobilimbia sensu stricto
Crustose lichens containing a trebouxioid alga; thallus granular or verruculose, sometimes sorediate; apothecia with a non-algal rim that is more like the disc than the thallus in colour and texture; exciple formed of cylindrical hyphae embedded in gel, the hyphae arranged fan-like as seen in cross-section; hymenium formed of mostly straight, unbranched paraphyses embedded in gel, sometimes pigmented in upper portions; hypothecium colourless or dark pigmented; asci clavate, with a distinct, IKI+ medium blue tholus containing a paler, bluntly conical axial mass; spores colourless, 8 per ascus, elliptical-fusiform, usually with three transverse septae.
References: Ekman 1996; Ekman 2004c.
| 1a. | Thallus sorediate; epihymenium and hypothecium pale brown; spores 13-28 × 4-5 µ …Mycobilimbia epixanthoides |
| 1b. | Thallus lacking soredia; apothecial pigmentation various; spores various …2 |
| 2a. | Apothecia whitish, pink, yellow or pale tan, without pigments as seen in thin section; spores 12-25 × 4-7 µ …Mycobilimbia carneoalbida |
| 2b. | Apothecia brown to black, with dark pigments as seen in thin section; spores 15-30 × 4.5-7 …Mycobilimbia tetramera |
Mycobilimbia carneoalbida (Müll. Arg.) Printzen
Thallus medium grey-green or whitish green, warty and granular; apothecia 0.4-1.2 mm wide, whitish pink-beige, the rim at first thick and prominent, but quickly receding, the disc at first exposed only as a tiny dot, but quickly expanding and becoming high-convex to subspherical; rim non-algal, colourless; hymenium 60-90 µ high, colourless; upper hymenium colourless; hypothecium colourless; paraphyses mostly unbranched; asci with a low, rounded axial mass in a tholus that is not much higher than wide; spores 12-25 × 4-7 µ, with 3 septae.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: Growing over mosses and bark at the bases of large Populus tremuloides (aspen), also at the bases of Pseudotsuga in aspen dripzones, lower to middle elevations.
Similar Species: Mycobilimbia tetramera has apothecial pigments and slightly larger spores.
Specimens: Björk 8645, 9957; Goward 94-929, 96-860.
Local Status: Common.
Mycobilimbia epixanthoides (Nyl.) Vitik., Ahti, Kuusinen, Lommi & T. Ulvinen
Thallus creamy green or olive-gray, areolate, the areoles disintegrating into creamy yellowish-green soredia 15-20 (‑30) µ wide; apothecia 0.3-0.8 (‑1.3) µ, light orangish brown or dark brown, with a thin, quickly receding rim; hymenium pale to light brown in upper portions; hypothecium pale brownish; spores elliptical, 4-celled, 13-28 × 4-5 µ.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: On mosses over the bases of Populus trunks, sometimes spreading onto adjacent bark. Lower elevations.
Similar Species: Megalaria brunnescens has soredia of a similar size and colour, but these remain in round soralia and react C+ orange-pink. Biatora chrysantha and B. chrysanthoides occur in similar habitats, but are also C+ pink, and have a deeper yellow colour.
Specimens: Björk 12250; Goward 94-923.
Local Status: Uncommon.
Mycobilimbia tetramera (De Not.) Clauzade, Diederich & Roux
Thallus medium grey-green or whitish green, warty and granular; apothecia 0.4-1.2 mm wide, whitish pink-beige, the rim at first thick and prominent, but quickly receding, the disc at first exposed only as a tiny dot, but quickly expanding and becoming high-convex to subspherical; rim non-algal, light to medium brown; hymenium 60-90 µ high, colourless; upper hymenium light to medium brown; hypothecium light to medium brown; paraphyses mostly unbranched; asci with a low, rounded axial mass in a tholus that is not much higher than wide; spores 15-30 × 4.5-7 µ, with 3 septae.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: Bases of large aspen and cottonwood (Populus) trunks, lower to middle elevations.
Similar Species: See notes under Mycobilimbia carneoalbida. Mycobilimbia berengeriana has darker apothecia and spores with 0-1 septae.
Specimens: Björk 8504, 10813.
Local Status: Common.