New species and records of intrahymenial parasites in the genus Helicogonium (Helicogoniaceae, Phacidiales)

Ten new species are described in Helicogonium and new records of eight known species are presented. The species are illustrated either by drawings or photographs, or in nine species by both. Helicogonium is a genus of intrahymenial parasites growing in the hymenium of other fungi, mainly discomycetes. Its members do not form excipular tissue and paraphyses, but only ascogenous hyphae and cylindric-clavate asci which are always inamyloid and (4‒)8-spored and often completely suppress the formation of meiosporangia of the infected host sporoma, mostly in discomycetes of the classes Leotiomycetes and Orbiliomycetes. The ascospores often germinate by forming minute conidia directly on one or rarely both spore ends through indistinctly enteroblastic conidiogenesis. Sometimes branched conidiophores with terminal phialides lacking collarettes occur in the hymenium of the host, sometimes along with the parasitic asci. The phialides have very short terminal pegs with minute periclinal wall thickenings and produce similar conidia as the parasitic asci. The genus Helicogonium can be divided into two groups, one forming sporogenous conidia inside the living asci (so-called ascoconidia) and one without ascoconidia (conidia formed on overmature ascospores after ejection or absent). The two groups are probably not phylogenetically distinct because of high morphological similarities between certain members of each group. One of the species presented here (H. trabinelloides) showed variation in this respect in some collections by forming ascoconidia in low quantity in some asci and no ascoconidia at all in others. One of the newly described species (H. subconniventis) appears to represent an exception within the genus: it seems to be a saprobe that forms its own excipulum and hamathecium instead of living parasitic in apothecia of a host. In its asci and ascospores H. subconniventis strongly resembles H. conniventis, an intrahymenial parasite of Durella connivens, except that these two elements have somewhat wider dimensions. To date, no ascertained molecular data are available for any species of the genus, because DNA isolation is impossible with the current method of Sanger sequencing which would require primers specific at the generic level.