Acanthostigmina Höhn., Sber. Akad. Wiss. Wien, Math.-naturw. Kl., Abt. 1 118: 1499 [39 repr.] (1909),

Saprobicon rotten wood, widespread in tropical regions. Sexual state:Ascomatasuperficial, solitary, scattered, some clustered, globose to subglobose, dark brown, ostiolate, surrounded by sparse, dark brown to black setae; setae relatively long, tapering to an acute apex. Peridium thick, comprising several layers oftextura angularis to subglobosa, inwardly comprising brown to reddish-brown, small brown cells of textura subprismatica. Hamathecium comprising numerous, filiform, septate, branched, hyaline and pale brown pseudoparaphyses, embedded in a gelatinous matrix. Asci 8-spored, bitunicate, broadly cylindric-subclavate, pedicellate, thickened at apex, without an ocular chamber. Ascospores 2–3-seriate, elongate, cylindric-fusiform, curved, tapering towards sub-rounded ends, less than 10-septate, slightly constricted at septum, hyaline when young and pale brown at maturity, some surrounded by a mucilaginous sheath, smooth-walled. Asexual state:Unknown.

Type species:Acanthostigmina minuta (Fuckel) Clem. & Shear

Notes: The genus Acanthostigmina was introduced by von Höhnel (1909a) with A. minuta (Fuckel)Höhn. as the type species. Saccardo (1883) had earlier included this species in Acanthostigma. Subsequently Acanthostigmina minutahas been placed in other genera (Barr 1980; Crane et al. 1998; Réblová and Barr 2000).In this study, we re-examined a specimen of Acanthostigmina minutumfrom Germany which Réblová and Barr (2000) considered to be representative of the species (Rehmexsiccatae, Ascomycete No. 1568, PAD) (Fig. Acanthostigmina minuta). Rehm’s exsiccataespecimen(BPI 624355) is characterized by dark brown to black ascomata, moderately stiff setae, broadly cylindric-subclavate, apically thickened asci and 5–9-septate, hyaline to pale brown ascospores with a thin mucilaginous sheath. This differs from the description of Acanthostigma minutumfrom the PAD neotype provided by Réblová and Barr (2000) in which the ascospores were more than 10-septate, hyaline and without a mucilaginous sheath, whereas in other characters they are rather similar. Unlike Acanthostigmina minuta, Acanthostigmaperpusillumhas ascomata covered by numerous setae; in addition these species differ in the size and shape of asci and ascospores.

Molecular data indicate that three non-type isolates of Acanthostigmina minutumfrom North America (ANM283, ANM818 and ANM880) formed a single clade distant from the Acanthostigma perpusillum clade (Promputtha and Miller 2010). Sánchez and Bianchinotti (2010) found a collection in Argentina identified as Acanthostigma minutum MVB 781 (BBB), which Sánchez et al. (2012) showed to cluster with Acanthostigmaperpusillum. In our multigene phylogenetic analysis, the North American strains of Acanthostigminaminuta (ANM810, ANM818 and ANM238) formed a monophyletic clade that clustered with two strains of Acanthostigminamultiseptatum (ANM475 and ANM665), although with weak support (Clade L, Tubeufiaceae family tree). We therefore treat Clade L as Acanthostigmina sensu stricto comprising A. minuta and A. multiseptatum).