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Background. In extant ecosystems, complex networks of ecological interactions between organisms can be readily studied. In contrast, understanding of such interactions in ecosystems of the geologic past is incomplete. Specifically, in past terrestrial ecosystems we know comparatively little about plant biotic interactions besides saprotrophy, herbivory, mycorrhizal associations, and oviposition. Due to taphonomic biases, epiphyte communities are particularly rare in the plant-fossil record, despite their prominence in modern ecosystems. Accordingly, little is known about how terrestrial epiphyte communities have changed across geologic time. Here, we describe a tiny in situ fossil epiphyte community that sheds light on plant-animal and plant-plant interactions more than 50 million years ago. Methods. A single silicified Todea (Osmundaceae) rhizome from a new locality of the early Eocene (ca. 52 Ma) Tufolitas Laguna del Hunco (Patagonia, Argentina) was studied in serial thin sections using light microscopy. The community of organisms colonizing the tissues of the rhizome was characterized by identifying the organisms and mapping and quantifying their distribution. A 200 X 200 mm grid was superimposed onto the rhizome cross section, and the colonizers present at each node of the grid were tallied. Results. Preserved in situ, this community offers a rare window onto aspects of ancient ecosystems usually lost to time and taphonomic processes. The community is surprisingly diverse and includes the first fossilized leafy liverworts in South America, also marking the only fossil record of leafy bryophyte epiphytes outside of amber deposits; as well as several types of fungal hyphae and spores; microsclerotia with possible affinities in several ascomycete families; and evidence for oribatid mites. Discussion. The community associated with the Patagonian rhizome enriches our understanding of terrestrial epiphyte communities in the distant past and adds to a growing body of literature on osmundaceous rhizomes as important hosts for component communities in ancient ecosystems, just as they are today. Because osmundaceous rhizomes represent an ecological niche that has remained virtually unchanged over time and space and are abundant in the fossil record, they provide a paleoecological model system that could be used to explore epiphyte community structure through time. [ABSTRACT FROM AUTHOR]

Premise of research. The Río Genoa Formation of Argentine Patagonia hosts Early Permian fossil assemblages that document levels of plant diversity rare among coeval floras. Ongoing work to exhaustively characterize the diversity of these assemblages is key to understanding Permian vegetation and plant evolution. A new fern type identified in the Río Genoa Formation exhibits a novel combination of characters that required taxonomic assessment. Methodology. Observations and measurements of vegetative and reproductive morphology of compression fossils were used in a comparative framework to address the taxonomic placement of the fossils. Pivotal results. The new fern, Floratheca apokalyptika gen. et sp. nov., is characterized by small pinnules with a free base, weakly lobed margin, highly decurrent midvein, and rarely branched lateral veins, as well as radially symmetrical synangia with stellate dehiscence, consisting of six spindle-shaped sporangia. This unique combination of characters distinguishes Floratheca from the more than 25 Permo-Carboniferous marattialean genera known from compressions. Floratheca exhibits variable synangium morphology during development and variation in pinnule base morphology due to a combination of adaxial-abaxial asymmetry of ultimate rachises and taphonomic effects. Conclusions. Floratheca is one of only three late Paleozoic bona fide marattialean compression genera endemic to Gondwana and the second late Paleozoic endemic South American marattialean with preserved fertile structures. Floratheca adds to an increasing diversity of fossils that diminish the disparity between the Southern and Northern Hemispheres, in terms of the extent and intensity of exploration of the plant fossil record, currently skewed taxonomically toward Northern Hemisphere taxa. Variability of synangium and pinnule base morphology in Floratheca cautions against potential taxonomic inflation produced by establishment of new taxa based on small numbers of specimens and incomplete understanding of development and taphonomy. [ABSTRACT FROM AUTHOR]