Karafit, Steven J. , Rothwell, Gar W. , Stockey, Ruth A. , Nishida, Harufumi .
A dryopterid fern with Onoclea-type stipe anatomy from the Eocene of North America.
Derived fossil filicalean ferns similar, or assignable to living species have been discovered throughout the Tertiary. The Middle Eocene Princeton Chert of southern British Columbia contains at least three of these ferns, one of which has an Onoclea-type stipe. Material consists of two permineralized rhizomes with attached stipe bases and adventitious roots, and isolated stipe segments. The rhizome has a parenchymatous pith, a ring of five amphiphloic cauline bundles and pairs of frond traces that diverge from adjacent cauline bundles in a 2/5 phyllotaxis. The cortex is also parenchymatous except at the periphery, where there is a well-developed sclerotic hypodermis. Prominent nests of large cells with black contents occur near the periphery of the pith and throughout the cortex. The stipe is characterized by a pair of hippocampiform bundles, and ground tissues that are similar to those of the rhizome. Roots are diarch with a parenchymatous and sclerenchymatous cortex. The vascular architecture of this fern appears to be unique among known Filicales. There are no gaps in the stele that result from the divergence of either frond or root traces, and there is no evidence that cauline bundles anastomose. Rather, the cauline bundles appear to extend through the rhizome independently of each other, and produce successive fronds traces on alternating tangents. Root traces diverge from the peripheral surface of cauline bundles as is characteristic of solenostelic filicalean species and dictyostelic tree ferns. Examination of the literature reveals that diverse filicalean vascular architectures have been grouped together as “solenosteles” and “dictyosteles”. The recently recognized array reveals that there is far more variation in filicalean stelar architectures than is popularly recognized. Although this newly recognized structural variation has some correlation with patterns of systematic diversity, the overall significance of fern vascular architecture has yet to be fully understood.
1 - Ohio University, Department of Environmental and Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
2 - Chuo University, Faculty of Science and Engineering, 1-13-27 Kasuga, Bunkyo, Tokyo, 112-8551, JAPAN
3 - University of Alberta, Department of Biological Sciences, CW 405 Biological Sciences Building, Edmonton, Alberta, T6G 2E9, Canada
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 2:45 PM