Unusual fungal reproductive units from the Lower Devonian Rhynie chert

Small, detached fungal reproductive units are almost ubiquitous in the Early Devonian Rhynie chert; however, only a few of these fossils have been described. Three morphologically distinctive types of spheroidal reproductive units occur in litter layers from the Rhynie chert. One of these is >250 μm in diameter and has a multi-layered wall; the outer surface is prominently fringed. Because specimens are borne laterally within the neck of a sporiferous saccule, this fossil is identified as an acaulosporoid glomeromycotan spore. The second reproductive unit (80–110 μm in diameter) is characterized by elongate-conical protuberances, while the third (<45 μm in diameter) possesses a thick outer wall layer or sheath traversed by tubular canals. The systematic affinities of these last two fossils remain unresolved. The reproductive units add to the inventory of easily recognizable fungal morphologies in the Rhynie chert and contribute to our understanding of fungal paleobiodiversity in early non-marine ecosystems.