Rhystidhysteron rufulum. Picture courtesy of Dr. E. Boehm

Rhystidhysteron rufulum is a poorly known mainly saprobic species capable of utilizing different substrata and occupying diverse habitats. It can also be associated with plant disease and occurs on the wood of living or dead dicotyledonous plants including stem cankers of citrus.  It produces superficial ascocarps (sexual structures) that are darkly pigmented and elongated with a longitudinal slit.  Upon maturity, the ascocarp opens to form an irregular cup from which sexual spores are released.  The sexual spores are darkly pigmented with rare muriform (longitudinal and horizontal) septations.  Due to its differences in ascocarp development and morphology from other hysteriaceous fungi Rhytidhysteron rufulum was traditionally classified in Patellariales (Dothideomycetes), but recent molecular phylogenetic analyses of multiple nuclear loci support it as being a member of the Hysteriales and closely related to the saprobic Hysterium pulicare (Boehm et al. 2009).

Dothideomycetes is the largest class of ascomycete fungi and contain species with diverse ecologies and nutritional modes, including plant pathogens, insect pathogens, lichens, marine fungi and saprobes. Two large orders contain the majority of economically important plant pathogens and Hysteriales is the sister order to one of them, the Pleosporales. Current phylogenetic hypotheses support a saprobic nutritional mode as ancestral in the class with multiple derivations of pathogens, autotrophic symbioses and unique life styles (Schoch et al 2009). The genome of R. rufulum, along with those from other saprobic taxa, will allow a greater understanding of the metabolic diversity of Dothideomycetes and the genomic diversifications associated with shifts between major ecologies and nutritional modes.

• Boehm, E.W.A., Mugambi, G.K., Miller, A.N., Huhndorf, S.M., Marincowitz, S., Spatafora, J.W. and C.L. Schoch.  2009. A molecular phylogenetic reappraisal of the Hysteriaceae, Mytilinidiaceae and Gloniaceae (Pleosporomycetidae, Dothideomycetes) with keys to world species. Studies in Mycology 64: 49-84.
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