Acanthostigma De Not., Sfer. Ital., 85 (1863)

Saprobic on dead wood. Sexual state:Ascomata superficial, scattered, globose to subglobose, mostly dark brown to black, occasionally collapsing when dry, with distinct dark setae, ostiolate. Peridium consisting of several-layers of textura angularis. Hamathecium with numerous, cellular, branching and anastomosing pseudoparaphyses. Asci 8-spored, bitunicate, fissitunicate, clavate, short pedicellate, broadly rounded and thickened at apex. Ascospores overlapping 2–3-seriate, fusiform, narrowly rounded at both ends, with one ofmiddle cells often broader than others, tapering towards the ends, trans-septate, straight or slightly curved, not-constricted or slightly constricted at septa, mostly hyaline, guttulate when immature, smooth-walled. Asexual state:Chlamydospores only known from culture(from Boonmee et al. 2011).

Notes: Acanthostigmasensu stricto is based onAcanthostigma perpusillum and the description given by de Notaris (1863). Réblová and Barr (2000) monographed and accepted six species in Acanthostigma. Morphologically all species are characterised by dark brown to black ascomata covered by dark setae; ascospores are usually broadly fusiform to clavate, asymmetrical, trans-septate and hyaline. The multigene phylogenetic analysis indicates that several Acanthostigma epithets are polyphyletic and belong within the Tubeufiaceae (Promputtha and Miller 2010; Boonmee et al. 2011; Sánchez et al. 2012).

The type species A. perpusillum was described and illustrated in Boonmee et al. (2011), while a new species,A. chiangmaiensis Boonmee & K.D. Hyde, was also introduced. Other species previously regarded as Acanthostigma (e.g. Acanthostigmafiliforme Promp. & A.N. Mill., A. minutum (Fuckel) Sacc.) are scattered in the phylogenetic tree, indicating that ascomata with setae have evolved on more than one occasion and is not a reliable character for determining genera in this family. We searched for herbarium specimens of Acanthostigma perpusillum from several herbaria (e.g. GE, PAD, RO and TO), but none areavailable for study. Réblová and Barr (2000) reexamined, described and illustrated this species and Boonmee et al. (2011) made drawings of the taxon based on Réblová and Barr (2000). The species has brown opaque, short setae on reddish-brown to dark brown ascomata. In this paper we treat Acanthostigma perpusillum strain UAMH 7237as an authentic specimen to represent Acanthostigma sensu stricto. Molecular analysis indicat that A. perpusillum and A. chiangmaiensis has moderate support (72% BS) in Clade E (Tubeufiaceae family tree). A putative strain of A. minutum (MVB 781 (BBB), Argentina, Sánchez et al. 2012) forms a long subbranch with A. perpusillum and A. chiangmaiensis but with weak support. Therefore, two species A. chiangmaiensis and A. minutum are accepted in the genus based on phylogeny (Fig. 2).Helicosporium sensu stricto forms a sister clade (Clade D). No asexual state has been reported for Acanthostigma perpusillum, however,A. chiangmaiensis formed chlamydospores in culture.AdditionallyA.filiformePromp. & A.N. Mill. and A.septoconstrictumPromp. & A.N. Mill.and A.multiseptatumdescribed in Promputtha and Miller (2010) are transferred to Neoacanthostigmaand Acanthostigmianarespectively based on morphology and molecular data.

Type species:Acanthostigma perpusillum de Not., Sfer. Ital.: 207 (1863)