MIXED ARBUSCULAR MYCORRHIZAE FROM THE TRIASSIC OF ANTARCTICA

Arbuscular mycorrhizae are the most ubiquitous of mycorrhizal fungi, t hat have formed mutualistic relationships with virtually almost all ma jor groups of vascular plants. Five genera of arbuscular endomycorrhiz al fungi are currently delineated, but fossil arbuscular mycorrhizae h ave been allied with only two, Glomus and Sclerocystis. A Triassic arb uscular mycorrhiza described inhabiting the roots of Antarcticycas was originally allied with Glomus. It is now known to be a mixed colony c omprised of fungi attributable to the suborders Glomineae and Gigaspor ineae of the Glomales, described as two new species. The fossil Gigasp orinean mycorrhiza is characterized by irregularly swollen intercellul ar and intracellular hyphae that are coiled extensively within the cel ls. Arbuscules have thick trunks and narrow branches. In the Glominean form, hyphal diameter is more uniform, with coiling rarely present. A rbuscules have thin trunks and fine branches. Vesicles may be lateral or terminal. Spores are not present; therefore, the probability of mor e than one species of each suborder being represented cannot be conclu sively demonstrated. This provides the first fossil representative of the Gigasporineae and supports current rDNA estimates of the age of th e lineage. Moreover, it is the first reported instance of a mixed colo ny of arbuscular endomycorrhizae in the fossil record.