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Hysterothecium of Hysterium pulicare. © Eric Boehm
Fungi classified in the Hysteriaceae Chevall. (Chevallier 1826) are defined by a specialized ascocarp termed the hysterothecium (Clements 1909). Hysterothecia are dense, persistent carbonaceous structures, distinctly navicular in outline, and bear a pronounced longitudinal slit running the length of the long axis of the fruitbody. Hysterothecia may be capable of opening partially to reveal a lenticular, disk-like hymenium or closing tightly in response to relative humidity, suggesting that some may be perennial, capable of spore discharge over prolonged periods (Lohman 1933). They can be immersed to erumpent or entirely superficial, solitary or gregarious, ellipsoid to greatly elongated, and are sometimes branched, triradiate or borne on a subiculum (Zogg 1962). In vertical section, hysterothecia are 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 (Barr 1987). The hamathecium is composed of persistent cellular pseudoparaphyses, often borne in a gel matrix, with tips darkened or branched at maturity to form an epithecium. Bitunicate asci are borne in a basal layer and at maturity are typically clavate to cylindric, bearing eight ascospores, overlapping biseriate, ranging from hyaline to dark brown, obovoid, clavate, ellipsoid or fusoid. Ascospores are highly diverse in septation and range from didymospores to phragmospores to dictyospores, at times surrounded by a gel coating, and often show bipolar asymmetry (Barr 1987). The family has been monographed by Zogg (1962). Detailed taxonomic keys and illustrations can be found on the web at http://www.eboehm.com/.
Current classification of the Hysteriaceae (Eriksson 2006) includes the following genera: Hysterium Fr. : Fr., Hysterographium Corda, Gloniopsis De Not., Gloniella Sacc., Glonium Muhl. : Fr., Farlowiella Sacc., and Hysterocarina Zogg, to which has been recently added Actidiographium Vassiljeva. The genera Hysteroglonium Rehm ex Lindau, Hysteropatella Rehm and Pseudoscypha Reid & Piroz., are tentatively included in the Hysteriaceae by Eriksson (2006). In addition to these, the genera Encephalographa Massal., Graphyllium Clem., and Hemigrapha (Müll. Arg.) R. Sant. ex D. Hawksw. were included by Kirk et al. (2001). Both coelomycetous pynidial states (e.g., Hysteropycnis, Aposphaeria) and dematiaceous hyphomycetous anamorphs (e.g., Coniosporium, Septonema, Sirodesmium, Sphaeronaema and Sporidesmium) have been described (Lohman 1931, 1933, 1934). Hysteriaceous fungi are panglobal in distribution, having been reported from Japan (Amano 1983), China (Teng 1933), the Russian Far East (Vasilyeva 1999a, b, 2000), South Africa (Lee & Crous 2003; van der Linde 1992), Argentina (Messuti & Lorenzo 1997, 2003; Lorenzo & Messuti 1998), Costa Rica (Checa et al. 2007), North America (Lohman 1933, 1937) and Europe (Zogg 1962). Although primarily lignicolous or corticolous, recently a saxicolous / terricolous and apparently lichenized species has been described from Tasmania (Kantvilas & Coppins 1997).