A fungal mycelium containing abundant endoconidia from the Lower Devonian Rhynie cherts of Scotland

Abstract

The Lower Devonian Rhynie cherts yield fossils of multiple types of fungal spores, but the systems that produced these spores are rarely preserved. Rhyniomycelium endoconidiarum gen. et sp. nov., a mycelium of uncertain affinity recently discovered in a degraded land plant axis from the Rhynie cherts, is characterized by endoconidia in virtually all hyphae, septa which typically occur in pairs and give off intrahyphal hyphae, and narrow hyphae ending in prominent, usually spheroidal heads that also contain, or consist of, conidia. The fossil hyphae closely resemble hyphae containing endoconidia of the extant ascomycete anamorph Geotrichum candidum (Saccharomycetales). Moreover, the fossil endoconidia appear to have originated from intrahyphal hyphae, precisely as in G. candidum. Conidiogenesis was probably thallic-arthric or thallic alternate-arthric. Rhyniomycelium endoconidiarum provides the oldest fossil evidence of endoconidia in fungi. Moreover, it links a dispersed spore type regularly encountered in the Rhynie cherts with a system in which spores of this type were produced. Documentation of such fossils contributes to our understanding of the evolution of reproductive processes in fungi.