Nematostigma
Nematostigma Syd. & P. Syd., Annls mycol. 11(3): 262 (1913).
Index Fungorum number: IF 3442; Facesoffungi number: FoF 07883, 6 morphological species (Species Fungorum 2022), no molecular data available.
Parasitic on living leaves, with superficial, large colonies, irregular, mycelium appressed to cuticle of host, with outwardly radiating hyphae, 6–8 µm wide, flexuous, branched, septate, dark brown, hyphopodia-like structures present, ostiole obscure. Sexual morph: Ascomata superficial, globose to subglobose, grouped, unilocular, with appendage hyphae or setae, septate, dark brown, surrounded by dark brown hyphae, seated on a subiculum or hyphal pack. Peridium comprising dark brown cells of textura angularis. Hamathecium comprising cylindrical, branched, septate, hyaline, pseudoparaphyses. Asci 8-spored, bitunicate, broadly ellipsoid, oval to clavate, sessile or with short pedicel. Ascospores 2–3-seriate, elongate, broadly cylindric-fusiform, slightly curved, tapering towards sub-rounded and asymmetrical ends, multi-septate, hyaline, pinkish when stained in 5% KOH, with thin gelatinous sheath, smooth to rough-walled with minute guttules. Asexual morph: Unknown (adapted from Boonmee et al. 2017).
Type species: Nematostigma obducens Syd. & P. Syd.
Notes: Nematostigma is characterised by superficial, globose to subglobose ascomata, broadly ellipsoid, oval to clavate asci and elongate, broadly cylindric-fusiform, slightly curved ascospores with thin gelatinous sheath. Sydow and Sydow (1913) treated Nematostigma in Sphaeriaceae based on the dark brown, sparse setae, spherical ascomata and hyaline, multiseptateascospores. Hansford (1946) studied the type specimen N. obducens and transferred Nematostigma to Parodiopsidaceae (= Parodiellinaceae) based on the mycelium penetrating into the leaf tissues lacking haustoria. Arx and Müller (1975) transferred Nematostigma to Dimeriaceae based on its parasitic lifestyle, superficial mycelium, hyphae penetrating host tissues, solitary ascomata with a subiculum, bitunicate asci and colorless to pigmented, septate ascospores. Eriksson and Hawksworth (1993) followed the treatment of Arx and Müller (1975). Hawksworth et al. (1995) transferred Nematostigma to Pseudoperisporiaceae and this was followed by subsequent authors (Bar 1997, Kirk et al. 2008, Lumbsch & Huhndorf 2010, Hyde et al. 2013). Boonmee et al. (2017) examined the holotype of N. obducens (S-F10256) and placed Nematostigma in a new family Nematotheciaceae based on morphology namely dark brown, sparse setae, spherical ascomata, and hyaline, multiseptateascospores. Nematostigma is a distinct and type genus of Nematotheciaceae. Molecular data is needed to confirm the taxonomic placement of Nematostigma.
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