Jud, Nathan A. , Rothwell, Gar W. , Stockey, Ruth A. .
Fossil evidence for the genus Todea: implications for the phylogeny of Osmundaceae.
Lower Cretaceous (Hauterivian - Valanginian) sediments of Vancouver Island, British Columbia, Canada have yielded the first fossil evidence for the genus Todea (Osmundaceae). The specimen is preserved by calcareous cellular permineralization in a greywacky sandstone matrix. The fossil consists of an anatomically preserved rhizome that branches near the apex, and that displays the diagnostic anatomical characters of the genus Todea. The stem stele is dictyoxylic, showing up to eight bundles around an sclerechymatous pith. Leaf bases diverge from the bundles in a typically osmundaceous pattern. Each leaf base displays a heterogeneous ring of sclerenchyma around a C-shaped xylem trace with 2-6 protoxylem strands. Within the adxial concavity of each trace is a single sclerenchyma bundle that becomes C-shaped as the leaf diverges from the stem. Sclerotic cortex is heterogeneous with indistinct outer margin. An adventitious root diverges with each leaf base. The roots wind obliquely through the cortex before emerging and extending into the marix. The root xylem is diarch. The rhizome represents a new species of Todea consisting of a branching stem, adventitious roots, and leaf bases. A cladistic analysis performed by addition of the new species and of morphological characters to a previously published rbcL gene sequence matrix supports the assignment the fossil to the genus Todea and the hypothesis that the genus Osmunda represents a paraphyletic assemblage within the monophyletic family Osmundaceae.
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1 - Ohio University, Department of Environmental and Plant Biology, Porter Hall, Athens, OH, 45701, USA
2 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
3 - University of Alberta, Department of Biological Sciences, Biological Sciences Centre, Cw 405, Edmonton, Alberta, T6G 2E9, Canada
Presentation Type: Oral Paper:Papers for Sections
Location: Williford A/Hilton
Date: Monday, July 9th, 2007
Time: 10:15 AM