Rhizophydites matryoshkae gen. et sp. nov. (fossil Chytridiomycota) on spores of the early land plant Horneophyton lignieri from the Lower Devonian Rhynie chert

Abstract

Premise of research: As our understanding of the importance of fungi in ecosystems today increases, we are still in the early stages of appreciating their roles in the past. The famous Early Devonian Rhynie chert contains a remarkable diversity of fungal fossils and copious evidence of fungal interactions; however, only relatively few of them have been described. Methodology: Thin sections of the chert were studied at high magnification in transmitted light. Images of fossils were captured digitally and processed in Adobe Photoshop. Pivotal results: A distinct eucarpic, monocentric chytrid (Chytridiomycota), Rhizophydites matryoshkae gen. et sp. nov., occurs on partially degraded in situ spores of the early land plant Horneophyton lignieri. Zoosporangia are epibiotic, usually spheroidal and less than 30 μm in diameter, and inoperculate, and they possess one to four discharge papillae or short tubes. Small bodies present within and outside many of the zoosporangia are suggestive of encysted zoospores and germinating zoospore cysts. Several specimens comprise two or more successive generations of zoosporangia occurring one inside another, a feature that allows for a direct comparison of the fossils with modern Rhizophydium (Rhizophydiales). Conclusions: The discovery of R. matryoshkae interacting with the spores of H. lignieri expands our knowledge of the biological relationships that define complexity in early continental ecosystems and provides a new calibration point that can be used to align molecular clock estimates with fossil evidence in the discussion of chytrid evolution.