A CYANOLICHEN FROM THE LOWER DEVONIAN RHYNIE CHERT

The 400 million-year-old Rhynie chert has provided a wealth of informa tion about various types of fungal interactions that existed in this E arly Devonian paleoecosystem. In this paper we report the first unequi vocal evidence of a lichen symbiosis from the Rhynie chert. Specimens of a new genus. Winfrenatia, consist of a thallus of superimposed laye rs rs of aseptate hyphae and, on the upper surface, numerous uniform d epressions. Extending into the base of each depression are hyphae that form a three-dimensional netlike structure. Enclosed within each of t he net spaces is a coccoid cynnobacterium, each cell of which is surro unded by a thick sheath. These photobiont cells divide in three planes , resulting in cell clusters of up to perhaps 64 individuals. The phot obiont is parasitized by the fungus in the base of each net as new cya nobacterial cells are formed distally. Reproduction is by endospores a nd soredia. Affinities of the mycobiont appear closest to members of t he Zygomycetes, while the photobiont is most similar to coccoid cyanob acteria of the Glococapsa and Chroococcidiopsis types. We speculate th at this cyanobacterial symbiosis was well adapted to exploit and colon ize new ecological niches,especially in the periodically desiccated en vironment postulated for the Rhynie chert paleoecosystem.