Innovations in organismal botany - a tribute to the pioneering studies of Donald A. Eggert
Tomescu, Alexandru .
Recognition, reconstruction, and characterization of ancestral filicalean ferns.
In the late 50's and early 60's, when Don Eggert turned his attention to the fossil record of ferns, filicalean fern diversity included only extant families and rare hints of putative leptosporangia in Carboniferous fossils. The Coenopteridales, an extinct pteridophytic group comprising small, monostelic plants, were regarded as potential intermediates between the basal trimerophytes and living ferns. The four families of coenopterid ferns (Stauropteridaceae, Zygopteridaceae, Botryopteridaceae, Anachoropteridaceae) were based on detached vegetative segments, with little knowledge of fertile parts, and many suspected that this classification, as well as the order as a whole, were artificial constructs. While there was growing agreement that coenopterids may, in fact, represent several distinct lineages, Eggert was the first to produce plant reconstructions that highlighted the need for reconsideration of coenopterid classification and initiated the disintegration of the order. More important, his reconstructions which reconciled coenopterid vegetative parts with newly discovered fertile structures, showed that some coenopterids were in fact filicalean ferns belonging to two new families: the Tedeleaceae, based on the zygopterid Ankyropteris, and the Sermayaceae, based on anachoropterid plants. Continued work on the coenopterid plexus in the vein pioneered by Eggert led to reconstruction of several other taxa and ultimately generated a novel understanding of Devonian-Carboniferous fern diversity and relationships. Disintegration of the Coenopteridales resulted in the establishment of two new orders, the Stauropteridales and Zygopteridales, as well as the recognition of six extinct filicalean families which form what came to be called the 'first filicalean radiation': the old Botryopteridaceae and Anachoropteridaceae, Eggert's Tedeleaceae and Sermayaceae, and the Psalixochlaenaceae and Kaplanopteridaceae. These add considerably to filicalean taxonomic diversity and contribute a wealth of morphologies featuring combinations of characters absent in living filicales. Perhaps most important, disintegration of the Coenopteridales and the novel combinations of characters of extinct filicaleans have allowed for reevaluation of euphyllophyte phylogenies, leading to exciting new perspectives that challenge the dogma on relationships within the group.
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1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Lindell D/Chase Park Plaza
Date: Tuesday, July 12th, 2011
Time: 2:00 PM