A fossil peronosporomycete oogonium with an unusual surface ornament from the Carboniferous of France.

A new fossil peronosporomycete from the upper Visean (Mississippian) of France occurs as a globose oogonium at the tip of a thin-walled hypha. The oogonium surface is prominently ornamented by densely spaced, long and subtle, straight or once to several times furcated thread-like extensions; many possess an opaque, bulb-like swelling at base. Antheridia adpressed to the oogonium are clavate and paragynous. This fossil represents only the third record of an unequivocal peronosporomycete from the Carboniferous, and thus provides important details about the evolutionary history of this group of organisms.