Stanich, Nicholas A. , Rothwell, Gar W. , Stockey, Ruth A. .
Early Cretaceous Equisetum fossils confirm that the modern evolutionary radiation was well underway 136 million years ago.
Three types of stems assignable to the genus Equisetum have been recovered from an extremely diverse flora preserved in carbonate marine concretions deposited at the Valanginian/Hauterivian boundary on Vancouver Island, British Columbia, Canada. These 136 million year old fossils represent the most ancient evidence for Equisetum based on anatomical characters. Two morphotypes are aerial shoots, while the third conforms to the features of an underground rhizome. All three are 1-2 mm in diameter and display a fluted margin in cross sections that represents ridges and furrows along the stem. Internal anatomy is distinctly modern in appearance, showing a hollow pith that is surrounded by an equisetostele. Peripheral cortical tissues include prominent sclerenchyma and vallecular canals. Nodes display a sheath of highly fused leaves, a nodal diaphragm, and branches. Bands of surficial stomatal complexes occur at the margins of furrows in one morphotype, suggesting assignment of that species to the subgenus Equisetum. The small size of the underground rhizome and irregular pattern of branching suggest that at least one of these Equisetum species was a small plant with morphology similar to the living E. scirpoides.
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1 - Ohio University, Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, 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
Date: Monday, July 28th, 2008
Time: 8:45 AM