Protologue type data: Type: Portugal; Azores, Terceira, N of Angra do Heroismo, E of Bagacina, Algar do Carvão, hilly area near cave, with shrubs, including Erica, 38° 43.69' N; 27° 12.98' W, on Erica, 485 m, 03.07.2014, P. & B. van den Boom 51850 (holotype: B; isotype: hb. v.d.Boom).

Type locality: Portugal, Azores, Terceira, N of Angra do Heroismo, E of Bagacina, Algar do Carvão, hilly area near cave, with shrubs, on Erica, 485 m, 3 July 2014, P. & B. van den Boom 51850 (B - holotype; van den Boom - isotype).

Type locality coordinates: 38°43.69'N, 27°12.98'W.

ITS barcode: Data lacking.

Description: Lichen. Thallus crustose, continuous, greenish grey, very thin, up to 0.1 mm thick, often almost indistinct; prothallus absent; upper surface smooth to slightly shiny, pale to moderately greyish brown; photobiont chlorococcoid, cells of 5 to 12 µm in diam. Apothecia scattered, up to 0.25 mm in diam., disc at first slightly convex but becoming strongly convex soon, dark brown, margin very thin, slightly paler brown than the disc, but soon disappearing; excipulum lecideine, not cellular, inner part pale brownish, base of the apothecia sometimes with a pale rim of outwardly directed hyphae; epihymenium, dark reddish brown, paler in KOH; hymenium ca. 55-70 µm high, hyaline; hypothecium dark brown; paraphyses strongly conglutinated, cells in the middle of the hymenium 1.5-2 µm in diam., simple to sometimes branched in the upper part, apices brown pigmented, widened up to 3 µm; asci Byssoloma-type, 8-spored, 25-37 x 15-20 µm; ascospores (17-)20-25 x (4-)4.5-5.5 µm, (3-)5-septate, ellipsoid, always well developed and abundantly present. Pycnidia unknown (van den Boom 2016: 203).

Photobiont: Data lacking.

Chemistry: Thallus K-, C-, KC-, P-; no chemical compounds detected (van den Boom 2016: 203).

Ecology: Corticolous on Cryptomeria japonica and Erica.

Distribution type: Endemic on Terceira (Azores, Portugal).

Taxonomy: Byssoloma fuscum is the most similar with B. marginatum (Arnold) Sérus., but it is much smaller in habitus having thinner thallus and smaller apothecia, it appears as B. marginatum. This latter has wider apothecia (up to 0.7 mm in diam.) with a rather conspicuous, persistent pale margin and smaller ascospores, 12-18 x 3-5 µm, always 3-septate. Fellhaneropsis myrtillicola (Erichsen) Sérus. et Coppins, is easily overlooked for the new species, because it has also small dark apothecia of 0.1-0.2(-0.3) mm, which are even convex and immarginate when mature, but these apothecia have mostly a bluish tinge. The ascospores are different, oblong-fusiform 16-28(-34) x 3-4 µm, 3(-5)-septate (van den Boom 2016: 203).

Note:

Distribution Database: Distributions

Distribution Database: Discover Life

Picture Database: Tropical Lichens

Molecular Database: Genbank

Synonym Database: Index Fungorum

Synonym Database: Mycobank