Hexagonella
Hexagonella F. Stevens & Guba ex F. Stevens, Bulletin of the Bernice P. Bishop Museum, Honolulu, Hawaii 19: 89 (1925).
Index Fungorum number: IF 2334; Facesoffungi number: FoF 01935, 1 morphological species (Species Fungorum 2022), no molecular data available.
Epiphytic on upper surface of leaves of Pelea rotundifolia. Sexual morph: Mycelium superficial, branched, forming a flattened, net-like thallus. Ascostromata scattered, solitary, superficial, with little cuticular connection, dark brown, rounded, plane, cushion-like, glabrous, multi-loculate, with each ascus forming in a locule, which is a ‘cell’ in a network-like structure, comprising a disk, with dense, woven mycelium, the central disk surrounded by irregular periphery of sparsely interwoven, loosely, branched, spreading hyphae, lacking ostioles. Peridium composed of a thick, hexagonal, mesh-like structure, with standing hyphae. Asci 8-spored, solitary, scattered in hexagonal cell-meshes, not covered by perithecia, each ascus resting in a space between the sterile cells. Ascospores overlapping, brown, ellipsoidal to oblong, 2-septate, constricted at the septum, broadest at the lowest cell, thick and smooth-walled. Asexual morph: Unknown (adapted from Stevens 1925, Phookamsak et al. 2016).
Type species: Hexagonella peleae F. Stevens & Guba ex F. Stevens
Notes: Hexagonella is characterised by scattered, solitary, superficial cushion-like ascostromata, 8-spored asci scattered in hexagonal cell-meshes and ellipsoidal to oblong, 2-septate ascospores (Stevens 1925, Phookamsak et al. 2016). Hexagonella resembles Ascocorticium in having cushion-like ascostromata, ellipsoidal to oblong asci but it can be differentiated by having asci arranged in hexagonal cells, with each ascus separated by sterile hyphae (Stevens 1925). Hexagonella also resembles Myriangium in forming rounded, cushion-like ascostromata and asci arranged in a single-layered thallus but differs in that the latter forms spherical, pulvinate and discoid ascostromata (Arx & Müller 1975). Hexagonella is also similar to Saccardia but can be differentiated in that the latter forms discoid ascomata, composed of isodiametric or irregular cells (Arx & Müller 1975). Stevens (1925) placed Hexagonella in Gymnopeltineae based on the solitary asci with flat, thin, soft ascomata. Arx and Müller (1975) referred Hexagonella in Schizothyriaceae based on the superficial, flattened, circular to ellipsoid ascostromata with ascus forming in locule in a network-like structure. This treatment was followed by several authors (Kirk et al. 2008, Lumbsch & Huhndorf 2010; Hyde et al. 2013, Wijayawardene et al. 2014). Phookamsak et al. (2016) re-examined the type specimen H. peleae from ILLS and microslides of ascomata from BPI and reported that the slide differed from the original description and iconotype. The authors followed Arx and Müller (1975) and treated Hexagonella in Schizothyriaceae based on morphology. Hexagonella is a distinct genus in Schizothyriaceae based on morphology. Sequence data is lacking. The type species of Hexagonella need to be recollected to confirm the correct taxonomic placement of the genus.
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