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(American Journal of Botany. 2009;96:323-335.) doi: 10.3732/ajb.0800295 © 2009 Botanical Society of America, Inc. |
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Special Invited Papers |
2 Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 3 Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701 USA
ABSTRACT
A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic.
Key Words: angiospermy • corystosperms • Cretaceous • cupule • Petriellaea • seed ferns
Received for publication 29 August 2008. Accepted for publication 18 November 2008.
FOOTNOTES
1 The authors thank A. Klymiuk, University of Alberta, for the AMIRA reconstructions; G. Cranham, S. Hubbard, T. Henrich, J. Morin, G. Beard, and M. Trask (Vancouver Island Paleontological Society and British Columbia Paleontological Alliance) for help in the field; and T. N. Taylor, University of Kansas, for the loan of Petriellaea specimens. This work was supported in part by Natural Sciences and Engineering Research Council of Canada grant A-6908 to R.A.S. and National Science Foundation Grant EF-0629819 to G.W.R., G. Mapes, and R.A.S.
4 Author for correspondence (e-mail: ruth.stockey{at}ualberta.ca)
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