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Abstract Detail


Evolution of Flower Development: from Phenotypes to Genes

Rudall, Paula, J. [1].

The inflorescence-flower boundary: insights from three phylogenetically diverse case-studies.

The current year (2007) is the centenary of a benchmark paper on floral evolution (ArberĀ and Parkin 1907), which used new paleobotanical discoveries to consolidate the euanthial concept, rather than the then-prevalent Englerian pseudanthial concept. Since the inflorescence-flower boundary is central to both theories, and hence to the nature of the flower, it is timely to revisit this subject in the light of new techniques and phylogenetic discoveries. In this paper, three case studies are investigated from distantly-related angiosperm lineages (eudicot, monocot, and early-divergent angiosperm) that display indistinct inflorescence-flower boundaries. Comparative ontogenetic and morphological data are evaluated in a phylogenetic context to establish hypotheses that are testable using developmental genetics. In the eudicot Euphorbia, the cyathium represents a flower-like structure that is apparently derived from an inflorescence by condensation. By contrast, in the monocot Triuridaceae, the female reproductive unit is inflorescence-like and apparently derived from a flower by loss of determinacy in the central whorl. Both cases show developmental shifts from centripetal to centrifugal initiation and morphological novelties such as unusual filamentous structures, possibly provoked by new patterns of gene expression. In the third case-study, the newly-discovered early-divergent angiosperm Hydatellaceae, bisexual reproductive units (inflorescences) in some species resemble the inside-out flowers of Lacandonia (Triuridaceae) in possessing naked stamens surrounded by several naked carpels (though no close phylogenetic affinity is implied). In both taxa, reproductive units develop centrifugally, perhaps indicating a developmental constraint which ensures that the earliest-formed carpels are initiated close to the androecium. ArberĀ and Parkin (1907) considered all simple unisexual flowers, including naked (apetalous) flowers, to be derived from bisexual flowers by reduction. However, such a primarily gradualistic and angiosperm-centric view could be challenged in an evo-devo context that allows for non-gradual (saltational) morphological transformations, and hierarchical inflorescence-flower shifts.


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1 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kingdom

Keywords:
flower
ontogeny
angiosperm
development
Hydatellaceae
Euphorbia
pseudanthium.

Presentation Type: Symposium or Colloquium Presentation
Session: SY17
Location: Stevens 4/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:30 AM
Number: SY17001
Abstract ID:589


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