Silicified roots from the Triassic of Antarctica show features of extant vesicular-arbuscular mycorrhizae (VAM). Nonseptate fungal hyphae occur within and between well-preserved parenchymatous cells of the central cortex. Terminal and intercalary swellings comparable to chlamydospores and vesicles are also present within the roots. In addition, three-dimensionally branched structures nearly fill the host cell and resemble modem day arbuscles. Although possible mycorrhizae have been reported as early as the Devonian, and are widely accepted, fossil arbuscles, the most definitive feature of VAM, have not been previously described. The fungi associated with the Antarctic roots provide the most complete and convincing evidence for prePleistocene VA mycorrhizae in the fossil record. AMONG THE MORE provocative ideas emergent from recent studies of fossil fungi is the suggestion that the establishment of mycorrhizal relationships was pivotal in the emergence of the land flora (Pirozynski and Malloch, 1975). Because this theory implies the presence of a long history of mycorrhizal associations, abundant evidence might be expected from the fossil record. So far, however, such evidence is scanty, in part because fossil roots have received relatively little attention. Probably the most cited and widely accepted example of fossil mycorrhizae is that of Palaeomyces in the Rhynie Chert (Kidston and Lang, 1921). Most other putative mycorrhizae involve Carboniferous fungi and constitute a relatively large proportion of the reports of fossil fungi. However, many of these have been reevaluated and rejected (Cridland, 1962). More recently, paleobotanists seeking evidence for mycorrhizae have turned to scanning and transmission elecI Received for publication 30 December 1986; revision accepted 3 April 1987. The authors would like to acknowledge Ms. Kathlene B. Pigg and Dr. Edith L. Taylor, Department of Botany, The Ohio State University, who assisted in material preparation. We also thank Dr. Roland L. Seymour, Department of Botany, The Ohio State University, for much useful discussion. The late Dr. James M. Schopf collected and prepared much of the material used in this study. This research was supported in part by funds from the National Science Foundation (BSR-8516323 and DPP8213749) and from the Biological Nitrogen Fixation Project of the Indo-U.S. Science and Technology Initiative through cooperative aid Grant PNW 85-388 from the Pacific Northwest Station, U.S. Forest Service, to Oregon State University. Contribution No. 575 from the Institute of Polar Studies, The Ohio State University. Address reprints requests to Thomas N. Taylor. tron microscopy to supplement earlier light microscopy studies (e.g., Wagner and Taylor, 1982; Stubblefield and Taylor, 1985). Opinion regarding the existence of such associations in the Paleozoic is mixed, as is the evidence on which these reports are based (Stubblefield and Taylor, 1985). To date, more recent, pre-Cenozoic, fossil representatives of vesicular-arbuscular mycorrhizae have not been reported. Additional well-preserved examples of mycorrhizae spanning the geological column are needed if the presence and history of these associations is to be convincingly documented. In the present study the fungi in a single type of well-preserved Triassic root are examined. Fossil fungi, represented by hyphae, vesicles, chlamydospores, and arbuscles are compared with modem fungi, particularly those within the vesicular-arbuscular endomycorrhizae. These fungi are also compared with possible Paleozoic analogs from the Devonian and the Pennsylvanian that show many similar features. MATERIALS AND METHODS-Fungal-colonized roots are a common component of silicified nodules collected from the Fremouw Peak Formation near Fremouw Peak in the Beardmore Glacier region of Antarctica (see Smoot, Taylor, and Delevoryas, 1985). The locality is Triassic in age (Barrett, 1969), and is variously interpreted as early Triassic (Schopf, 1978) or early-middle Triassic (Collinson, Stanley, and Vavra, 1980). The material was collected in part in the 1970's by late James M. Schopf and other members of the The Institute of Polar Studies at The Ohio State University (Schopf,