Byssoloma brunneodiscum
Byssoloma brunneodiscum is a species of foliicolous lichen in the family Pilocarpaceae. Described in 2020 from specimens collected on Hainan Island, China, this lichen forms smooth, dull-green films on living leaves in montane rainforest understorys. It is distinguished by its brown to dark-brown fruiting discs surrounded by thick white margins and its production of a chlorinated xanthone compound in its tissues.
Taxonomy
Byssoloma brunneodiscum is a foliicolous member of the family Pilocarpaceae that was described in 2020 by Wei-Cheng Wang and Jiang-Chun Wei. Molecular analysis of mitochondrial small-subunit rDNA places it, together with B. annuum, B. melanodiscocarpum and B. rubrofuscum, in the well-supported B. subundulatum clade within Byssoloma. The holotype was collected by Wang on 6 September 2017 from Jianfeng Ridge,, at 960 m elevation. The specific epithet brunneodiscum refers to the brown that are characteristic of the apothecia of this species.Description
The thallus forms a smooth, continuous, dull-green film on living leaves and lacks a distinct marginal. Algal cells are, 5–7.5 μm in diameter. Apothecia are sessile, 0.3–0.5 mm wide, with a plane brown to dark-brown that is encircled by a thick, persistent white margin. Beneath the disc, the excipulum and basal tissue consist of loosely interwoven colourless hyphae studded with crystals that dissolve potassium hydroxide solution to produce a positive pink reaction; the is pale brown and measures 25–30 μm high. The hymenium reaches 40–50 μm tall; asci are 8-spored and amyloid, while the ellipsoid, colourless ascospores have three transverse septa and measure 11–14 × 3–4 μm.Asexual propagation occurs through, wart-like pycnidia that release non-septate, pear-shaped conidia 2–2.5 × 1.5 μm. Thin-layer chromatography detects the chlorinated xanthone compound 2,5,7-trichloro-3-O-methylnorlichexanthone in the thallus.