Extraordinary Preservation of Plants and Fungi: Symbiosis and Beyond

The fossil record is replete with examples of extraordinary preservation in plants, ranging from grana stacks in chloroplasts, nuclei, and various membrane systems to embryos, apical meristems, and delicate fungal structures. Well-preserved cells are known from organisms early in the evolution of terrestrial floras and extend to plants preserved in Carboniferous coal balls, as well as Permian and Triassic peats from Antarctica. Permineralization, in which tissue systems are preserved intact, can offer exceptional details about fossil plant development, plant responses to certain ecological conditions, and examples of evolutionary adaptations associated with multiple phases of land-plant organization. This extraordinary type of preservation has made it possible to make direct comparisons with extant plants and thus examine structure/function relationships in ancient ecosystems. For example, high-latitude growth rings from Permian and Triassic plants show a cellular pattern within the rings that indicate growth was limited by climatic variables which do not exist today. Well-preserved fungi have provided new opportunities to examine more ephemeral aspects of their biology, as well as a suite of complex interactions in ancient ecosystems such as the Rhynie Chert Lagerstätte. Such associations include examples of saprophytic, parasitic, and mutualistic interactions, including tritrophic interactions. Many of these persist today with similar symptoms and host responses, but with hosts that have repeatedly changed through time. For example, the evidence for mycorrhizal associations in early land plants is based on the occurrence of arbuscules, delicate hyphal extensions that are the sites of physiological exchange in modern fungi. The presence of mycorrhizal fungi in certain parts of some early land plants provides important details useful in deciphering stages in the evolution of the life history of these plants. Permineralizations and other examples of extraordinary preservation in fossil plants and fungi will be used to discuss the biology of these organisms.