<i>Rhizophydites bicornis</i> Nov. Sp. (Fossil chytridiomycota) from the Rhynie Chert, Scotland

Abstract Fungal spores from the Lower Devonian Rhynie chert are frequently colonized by other fungi; however, only a few of these colonizers have been described. Rhizophydites bicornis nov. sp., which occurs on certain thin-walled fungal spores, is monocentric and characterized by inoperculate zoosporangia that are broadly citriform or spindle-shaped, ovoid, inversely triangular, or irregular, up to 25 μm high and 40 μm wide, and usually lie with their long axis perpendicular to the point of insertion on the host. They typically have two lateral opposite discharge papillae. In some cases, secondary zoosporangia have developed from the walls of old sporangia. Similarities between R. bicornis and the extant Rhizophydium goniosporum and R. transversum (Rhizophydiales) are used to suggest affinities of the fossil to the Chytridiomycota.