Byssoloma brunneodiscum is a species of foliicolous (leaf-dwelling) lichen in the family Pilocarpaceae.[1] 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.
The thallus forms a smooth, continuous, dull-green film on living leaves and lacks a distinct marginal hypothallus . Algal cells are chlorococcoid , 5–7.5μm in diameter. Apothecia are sessile, 0.3–0.5mm wide, with a plane brown to dark-brown disc that is encircled by a thick, persistent white byssoid margin. Beneath the disc, the excipulum and basal tissue consist of loosely interwoven colourless hyphae studded with crystals that dissolve potassium hydroxide solution (KOH) to produce a positive pink reaction; the hypothecium is pale brown and measures 25–30μm high. The hymenium reaches 40–50μm tall; asci are 8-spored and amyloid, while the ellipsoid, colourless ascospores have three transverse septa and measure 11–14 × 3–4μm.[2]
The species is known only from montane rainforest on Hainan Island, China, where it grows sparsely on smooth leaf surfaces in the damp, shaded understory at around 960m elevation.[2]
1 2 3 4 Wang, Wei-Cheng; van den Boom, Pieter; Sangvichien, Ek; Wei, Jiang-Chun (2020). "A molecular study of the lichen genus Byssoloma Trevisan (Pilocarpaceae) with descriptions of three new species from China". The Lichenologist. 52 (5): 387–396. doi:10.1017/s0024282920000390.
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