Paleomycology of the Princeton Chert II. Dark-septate fungi in the aquatic angiosperm Eorhiza arnoldii indicate a diverse assemblage of root-colonizing fungi during the Eocene

Abstract

Tissues of the extinct aquatic or emergent angiosperm, Eorhiza arnoldii incertae sedis, were extensively colonized by microfungi, and in this study we report the presence of several types of sterile mycelia. In addition to inter- and intracellular proliferation of regular septate hyphae, the tissues contain monilioid hyphae with intercalary branching. These filamentous mycelia are spatially associated with two distinct morphotypes of intracellular microsclerotia. These quiescent structures are morphologically similar to loose and cerebriform microsclerotia found within the living tissues of some plants, which have been attributed to an informal assemblage of dematiaceous ascomycetes, the dark-septate endophytes. While there are significant challenges to interpreting the ecology of fossilized fungi, these specimens provide evidence for asymptomatic endophytic colonization of the rooting structures of a 48.7 million year old aquatic angiosperm.

• cerebriform
• dark-septate endophytes
• Leptodontidium
• microsclerotia
• monilioid
• paleomycology
• Phialocephala
• Princeton Chert

Acknowledgments

This research was supported in part by the National Science Foundation ( EAR-0949947 to T.N.T. and M.K.; OPP-0943934 to E.L.T. and T.N.T.) and the Department of Ecology and Evolutionary Biology, University of Kansas.

We gratefully acknowledge D. Randolph S. Currah for helpful discussion and Drs Ruth A Stockey and Gar W. Rothwell, who made samples of Princeton Chert available to us. Two anonymous reviewers provided commentary that appreciably improved the manuscript.