Keller, Harold W. , Everhart, Sydney E. .
Evaluation of fossil myxomycetes in amber: a myxomycologists’ perspective.
Myxomycete fruiting bodies and plasmodia have been described preserved in amber in the recent literature but lack verification by a myxomycologist. Some of these specimens are excellent examples of fossilized myxomycete fruiting bodies while others are unlikely to be myxomycetes at all. Baltic amber dating from the Eocene Epoch in the Tertiary Period approximately 35 to 40 million years ago has intact sporangia identified as Stemonitis splendens with well preserved parts evidenced by the hypothallus, stalks, columella, and branching and anastomosing capillitial threads forming a closed surface network. Similarly, Arcyria sulcata is another example with stalked sporangia showing a well developed capillitial network of coiled threads attached at the base to the calyculus. This specimen appears similar to the modern day species Arcyria denudata. Stalked structures also found in amber were assigned to the myxomycete Protophysarum balticum. However, these specimens have filaments and cellular parts that clearly rule out a myxomycete sporangium and more likely represent a calicioid lichen sometimes referred to as a “stubble lichen”. The plasmodium of a supposedly physaraceous myxomycete was described from Dominican Republic amber found in mines dated 35 to 45 million years ago. The general morphology includes a continuous section described as veins of a phaneroplasmodium and a network of vesicles that had sclerotized. Inside each spherule were 0 to 6 spherical inclusions considered nuclei that measured 8 to 24 Âµm in diameter. The nuclei of myxomycetes are characteristically much smaller and for Physarum polycephalum range from 2.5 to 7 Âµm in diameter. The images of scattered bubbles and nuclei attributed to a myxomycete plasmodium are problematic and highly doubtful when compared to living plasmodial stages observed on agar cultures. It is noteworthy that myxomycete fruiting bodies fossilized in amber have had few morphological changes in 40 million years.
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1 - University of Central Missouri and Botanical Research Institute of Tex, Department of Biology and Earth Science, Warrensburg, Missouri, 64093, U.S.A.
2 - University of Georgia, Department of Plant Pathology, Athens, Georgia, 30605, U.S.A.
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Superior A/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 1:45 PM