A new occurrence of saprotrophic oomycetes from the ca 307–303 million-years-old Grand’Croix Chert (Massif central, France)

The Grand'Croix Chert (Massif Central, France) contains an exceptionally well-preserved plant assemblage, notable for its diverse reproductive structures. It also preserves numerous fungi and a few fungus-like microorganisms, of which only one has previously been formally described as an oomycete. Here, we report <i>Kamounia striata</i> <i>gen. et sp. nov.</i>, based on exquisitely preserved fossil oogonia and antheridia from samples housed in the collections of the Paris and Stockholm natural history museums. The fossil is interpreted as saprotrophic on dead plant remains. It was studied and reconstructed three-dimensionally using confocal laser scanning microscopy and imaging software. Its main structural features suggest an affinity with <i>Peronosporomycetes.</i> This study adds to our knowledge of the evolutionary history of oomycetes, which is poorly documented in the fossil record, and highlights the importance of saprotrophy for understanding the evolution of pathogens, which is just beginning to be recognised in modern ecosystems.