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Abstract Detail


Paleobotanical Section

Taylor, David W. [1].

Organs First, Flowers Later: A new theory on the first flowers based on developmental and paleobotantical data.

Early Cretaceous flowers show great similarity in the structure of individual organs, such as tepals, stamens and carpels with short styles and small stigmas. Yet floral and inflorescence structure is much more variable, with some reproductive structures not clearly recognizable as flowers. Developmental data on inflorescences and flowers provide a genetic framework for reproductive structures in angiosperms. Review of Early Cretaceous angiosperm flowers shows that all groups of reproductive developmental control genes were present, but the variation in some characteristics indicates some were not as canalized as in living angiosperms. The reproductive axes are very variable and are only uniformly similar by being determinate, having male proximal and female distal and having flowers of similar age. The flowers are also variable but share having unelaborated perianth and hypogynous structure. The stamen is fully canalized and has dorsifixed, tetrasporangiate, dithecal anther with a broad connective and an apical tip attached to a short, unjointed filament. The carpel is also fully canalized and is apocarpous with short apical stigmas and little or no style. Molecular evidence for these genes suggests most existed in the angiosperm sister groups while fewer were uniquely angiospermous. Base on these new insights I proposed to a new Organs First, Flowers Later model for the evolution of angiosperm reproductive parts. The stages of the evolution of the flowers would start with the organs, then evolution of determinacy and bisexualization, followed by canalization into flowers and inforescences, and finally elaboration to the stereotypic floral types. Tetrasporangiate anthers on short filaments, and small, apocarpous carpels with small stigmas placed on reproductive axes were ancestral. Only later were these grouped into organs called flowers. Study of the living plants from the ANITA grade also supports this model and explains the great diversity of flowers in the most basally placed angiosperms. This model is testable by both the fossil record and studies of molecular control of living flowers.

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1 - Indiana University Southeast, Department of Biology, 4201 Grant Line Road, New Albany, IN, 47150

Keywords:
evolution
floral
development
Fossil.

Presentation Type: Oral Paper:Papers for Sections
Session: 23
Location: 555A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 9:30 AM
Number: 23007
Abstract ID:308


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