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Developmental and Structural Section

Richards, Jennifer [1], Bruhl, Jeremy J. [2], Wilson, Karen L. [3].

Understanding floral homology of mapaniid Cyperaceae: Development of reproductive structures in Exocarya sclerioides.

Recent phylogenetic studies of the Cyperaceae have identified the mapaniid clade as sister to the rest of the family. Homology of the reproductive units (RUs) and spikelet-like units (SLUs) of this clade to flowers and spikelets of other sedges is not clear; floral structures of the mapaniids have been described as single flowers and as condensed spikelets. Understanding homologies of the RUs and SLUs requires developmental studies, so we have examined development of these structures in the mapaniid Exocarya sclerioides. Fixed material of mature and developmental stages was studied in dissections and sectioned material and with scanning electron microscopy. Inflorescence branches terminated in a SLU. The first RU was usually borne in the axil of the sixth SLU bract. RUs had 4 leaf-like structures (LLSs): 2 lateral keeled LLSs, each associated with a stamen, an abaxial LLS also associated with a stamen, and an adaxial LLS. The gynoecium, which had 2 stylar branches and stigmas, occupied the center of the RU. SLUs produced 1 to 4 RUs. All RUs were axillary to bracts and all mature SLUs had unexpanded bracts and axillary RUs produced beyond the expanded RUs, so SLUs were racemose. RUs were hermaphroditic but could be male by abortion of the gynoecium. RUs developed from a single primordium that initiated the 2 lateral LLSs, then the 2 lateral stamens, then the 2 lobes of the gynoecium. Initiation of the abaxial LLS and stamen and of the adaxial LLS followed. We hypothesize that the RU is homologous to a reproductive branch that terminates in a hermaphroditic flower with 2 stamens and a single gynoecium; the 2 lateral LLS are halves of a deeply-divided prophyll. The additional LLSs are bracts on this cymose unit, while the abaxial stamen is a determinate branch.

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1 - Florida International University, Department of Biological Sciences, 11200 Sw 8Th Street, Oe167, Miami, Florida, 33199, USA
2 - University of New England, Botany, Centre For Ecology, Evolution And Systematics, Armidale, New South Wales, 2351, Australia
3 - Royal Botanic Gardens, Mrs Macquaries Road, Sydney, New South Wales, 2000, Australia

sedge flowers
sedge spikelets
sedge floral homology

Presentation Type: Oral Paper
Session: 16-5
Location: 400/Hilton
Date: Monday, August 15th, 2005
Time: 2:30 PM
Abstract ID:85

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