Bilimbia
Crust lichens containing trebouxioid algae; thallus smooth, verruculose or subsquamulose, dull whitish; apothecia convex, with a thin, inconspicuous, non-algal, excipular rim formed of thick-walled, cylindrical hyphae embedded in thick gel that swells outward and dissolves in K; hymenium formed of moderately branched and anastomosed paraphyses, pigmented; hypothecium usually distinctly pigmented; asci IKI+ dark blue in a hazy layer on the outer wall surface, with a well-thickened tholus having a sharply pointed ocular chamber, a dark blue tholar dome, and a darker blue tube (the tube is very hard to see owing to the dark blue outer wall and tholar stains); spores 8 per ascus, colourless, transversely septate, fusiform, with acute ends, with a warty outer layer.
Notes: The genus Myxobilimbia was raised by Hafellner & Türk (2001), using Lecidea lobulata Sommerf. as the type species. More recently, Veldkamp (2004) pointed out that the older name Bilimbia De Not. is available for use though it had been interpreted to have been used for a species of vascular plant in an earlier publication, as Bilimbia (Reede) Rchb. This first use of the name was invalidly published, so the name was first correctly published when it was applied to split Bilimbia sabuletorum from its original placement in Lecidea. Added to Bilimbia sabuletorum are species having an ascus with an IKI+ dark blue tube structure, a characteristic missing from Bilimbia sabuletorum. In other characters, some of these accessory species in Bilimbia also disagree with B. sabuletorum, such as their lack of an excipular gel that expands greatly in K, fusiform spores with acute ends, and the widely expanded paraphysis tips.
For these reasons, the genus Myxobilimbia is maintained for species of the Lecidea lobulata group, which are united by having an ascus similar to Porpidia-type, while Bilimbia is used for B. accedens, B. sabuletorum, and an undescribed species here referred to as B. rosea ined. The genus Mycobilimbia is also involved in this taxonomic model, with Mycobilimbia hypnorum and its close relatives being linked here with Myxobilimbia lobulata, despite the lack of blue granules in the exciple, which is supposed to mark M. hypnorum and relatives as a distinct group. The same ± Porpidia-type ascus found in Myxobilimbia hypnorum and Myxobilimbia lobulata, plus the presence in both of a warty outer coat on the ascospores, and overall similarity in apothecial morphology unite them and their related species within Myxobilimbia.
References: Clauzade & Roux 1985; Ekman 1996; Hafellner & Türk 2001; Veldkamp 2004.
| 1a. | Hypothecium pale to light brown; spores 18-32 × 5-6.5 µ, 3-septate; hymenium and exciple with light to medium orange-brown pigments, K+ pink-rose …Bilimbia rosea ined. |
| 1b. | Hypothecium generally medium to dark brown; spores averaging wider than in 1a, and often with more than 3 septae; any pigments brown, K- or K+ reddish, but not distinctly pink-rose …2 |
| 2a. | Apothecia 0.3-0.5 mm wide, brownish black; spores 25-30 × 6-8 µ; growing on bark, well above ground level …Bilimbia accedens |
| 2b. | Apothecia 0.3-0.8 mm wide, medium to dark brown; spores 18-40 × 5-8 µ; growing on moss, bark or detritus, on or near the ground …Bilimbia sabuletorum |
Bilimbia accedens Arnold
Thallus thin, whitish and scurfy, or immersed; apothecia dark brown to black, 0.2-0.8 mm wide, high-convex, constricted at the base, with a thin, quickly receding rim; hymenium dark greenish brown in upper portions, the paraphyses up to about 6 µ wide at the tip; hypothecium reddish brown; spores elliptical or fusiform, 20-45 × 5-9 µ, with 5-12 septae, with a warty outer layer.
Reactions: All spot tests negative.
Contents: No lichen substances known.
Habitat: On Thuja bark and on rough bark of Populus trichocarpa in humid, well-lit sites. Lower elevations.
Similar Species: Lecidea morula and “Strangospora” moriformis have simple, very numerous spores per ascus; Forms of Lecidea albofuscescens with weakly rimmed apothecia have a densely oil-inspersed hymenium and simple spores.
Specimens: Björk 15194.
Local Status: Rare.
Notes: The corticolous habit, smaller, darker apothecia, and often more numerously septate spores separate this species – albeit weakly – from B. sabuletorum.
Bilimbia rosea Björk ined.
Thallus smooth, areolate or granular, creamy whitish; apothecia medium brown or brownish pink, high-convex, constricted at the base, with a concolourous or contrastively light brown, thin and receding rim; hymenium light orange-brown throughout, K+ pink-rose, the paraphyses stout, up to 4.5 µ wide in upper portions; hypothecium colourless or pale brownish yellow; spores 17-32 × 5-6.5 µ, 3-septate, with a warty outer layer.
Reactions: All spot tests negative.
Contents: Unknown
Habitat: Creeping over mosses, or growing on wood of a log; known from two collections. Lower elevations.
Similar Species: No other local epiphytic crust has brown, K+ pink apothecial pigments.
Specimens: Björk 10802, 12446.
Local Status: Rare.
Notes: Known only from the study area.
Bilimbia sabuletorum (Schreb.) Arn.
Thallus granular or in part smooth and scurfy, creamy whitish or greyish olive; apothecia light pinkish brown or medium to dark brown or blackish, with a thin, receding rim more or less coloured like the disc; hymenium colourless or light brown in upper portions, the paraphyses up to 6 µ wide at the tip; hypothecium dark red-brown (less often light brown); spores 18-40 × 5-8 µ, 3- to 7-septate with a warty perispore.
Reactions: Spot tests all negative.
Contents: No known lichen substances.
Habitat: Growing over mosses or detritus, or on bark or wood near or on the ground in lower to (rarely) upper forested elevations.
Similar Species: Mycobilimbia species usually have paler or darker apothecia, and lack a warty perispore. Members of the “Mycobilimbia” hypnorum group have simple or few-septate spores also without perispores.
Specimens: Björk 8503, 11302.
Local Status: Occasional.
Notes: See comments under Bilimbia accedens.