Hysterium
Hysterium Pers., Tent. disp. meth. fung. (Lipsiae): 5 (1797).
Index Fungorum number: IF 2464; Facesoffungi number: FoF 0004, 47 morphological species (Species Fungorum 2022), 16 species with molecular data.
Lignicolous corticolous, commonly on well-decorticated hardwoods, rarely on conifers. Sexual morph: Ascomata defined by dense, persistent, thick-walled, carbonaceous hysterothecia, distinctly navicular in outline, bearing a pronounced longitudinal slit. Hysterothecia erumpent to entirely superficial, solitary, or gregarious, ellipsoid to greatly elongated. Peridium in vertical section, globose to obovoid, typically with a thick, three-layered peridium, composed of small pseudoparenchymatous cells, the outer layer heavily encrusted with pigment and often longitudinally striated on the surface, the middle layer lighter in pigmentation and the inner layer distinctly thin-walled, pallid, and compressed. Hamathecium composed of persistent cellular, hypha-like hyaline, septate, pseudoparaphyses, often borne in a gel matrix, with tips darkened or branched at maturity above the asci. Asci 8-spored, borne in a basal layer, typically clavate to cylindric at maturity, bitunicate, fissitunicate, with a distinct ocular chamber. Ascospores phragmospores 3- or more transversely septate, with cells often constricted at the septum, especially the median septum, pigmented versicolorous or concolorous, often showing bipolar asymmetry, without swollen supra-median cell, overlapping bi-seriate, obovoid to clavate, ellipsoid or fusoid, sometimes with a thin gel coating when young. Asexual morph: see notes below (adapted from Hyde et al. 2013).
Type species: Hysterium pulicare Pers.
Notes: Tode (1784) first recognized the group of fungi characterised by a longitudinal slit, that he named “Venusschwämme” (Boehm et al. 2009). Hysterium was formally introduced by Persoon (1797) with H. pulicare as type species. Hysterium is characterised by carbonaceous erumpent to entirely superficial hysterothecia, typically clavate to cylindric asci and 3- or more transversely-septate ascospores. Zogg (1962) suggested two morphological types within Hysterium. Type I is characterised by 3-septate phragmospores, and comprises the versicolorous type species H. pulicare Tode, H. angustatum Pers. both occurring in the temperate zones of both hemispheres, H. vermiforme reported from Africa and H. microsporum reported from North America and China (Teng 1933, Hyde et al. 2013). Lohman (1934) justified the inclusion of H. hyalinum in the Type I morphological type by reporting that pigmentation occur later in the maturation of the 3-septate ascospores even though Zogg (1962) did not accept H. hyalinum. Type II is characterised by a different phragmospore, with five or more septa, and in which a swollen cell form in the supramedian or, sometimes some distance up from the median septum. Type II comprises H. insidens, H. sinense, H. magnisporum with 7-septate, with three of the septa crowded to each end, the two central cells much larger. Zogg (1962) accepted Hysterium velloziae having up to 21 septa at maturity. Checa et al. (2007) described H. asymmetricum from Costa Rica characterised by an outer centrum tissue pigmented red, and 3-septate phragmospores, showing an extended basal cell. Messuti and Lorenzo (1997) described H. andinense from Austrocedrus chilensis in Argentina. Boehm et al. (2009) provided the combination Mytilinidion andinense based on phylogenetic analysis and transferred H. andinense to Mytilinidiaceae. Boehm et al. (2009) also described Hysterium barrianum and reported that Hysterium is a highly polyphyletic genus which implies that the development of pigmented phragmospores in the hysterothecia might have occurred at least three times within the Pleosporomycetidae. Boehm et al. (2009) also reported that molecular data do not support the two morphological types as proposed by Zogg (1962) since in their analysis, H. pulicare, H. angustatum, and H. vermiforme corresponding to Type I formed a monophyletic group but also contained H. barrianum which belongs to Type II. The authors transferred two species H. sinense and H. insidens to another genus Oedohysterium as they formed a distinct lineage distant to Hysterium. Hysterium differs from Oedohysterium in that the latter is characterised by presence of a swollen supra-media cell, which is lacking in Hysterium. Hysterium is morphologically and phylogenetically a distinct and type genus of Hysteriaceae. Molecular markers available for Hysterium are ITS, LSU, SSU, RPB2 and TEF-1.
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