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Abstract Detail

Understanding plant evolution: morphology to molecules

Endress, Peter K. [1].

The immense diversity of floral monosymmetry and asymmetry across angiosperms.

Floral monosymmetry and asymmetry are expressed in very different ways. Monosymmetry may encompass different floral regions and be expressed in different directions with regard to the next-higher-order axis of the inflorescence. It involves differential change in proportions of organs or groups of organs, or differential loss or gain of organs. It is useful to distinguish between active and passive monosymmetry, monosymmetry by reduction, and developmentally transient monosymmetry. Active monosymmetry is based on evolutionary change in structure in flowers with radially arranged organs mainly shaped by hymenopteran pollination. Passive monosymmetry occurs in dense inflorescences of simple flowers, such as in catkins, in which monosymmetry is superimposed on the flowers by the architecture of the entire inflorescence, mainly the subtending bracts covering the flowers (Fagales). Monosymmetry by reduction occurs when the number of organs of a category is reduced to one (one stamen in some Chloranthaceae or Lacistemataceae). Transient monosymmetry is present in early developmental stages of some polysymmetric flowers in racemose inflorescences. Floral monosymmetry occurs in many clades of angiosperms. In some it appears as a key innovation that led to a great diversification, expressed at family or order level (Orchidaceae, Leguminosae, Lamiales). In others it did not spur diversification, especially in those with passive monosymmetry, where monosymmetry appears merely as a by-product of the evolution of the characteristic inflorescence architecture. Floral asymmetry is also diverse but is much more rare than monosymmetry. Instances are enantiostyly (some Leguminosae, Haemodoraceae) or other forms, often together with monochasial partial inflorescences (some Zingiberales, Commelinaceae, Vochysiaceae). The structural diversity and systematic distribution of floral monosymmetry and asymmetry suggests that both encompass forms that are non-homologous not only in terms of phylogenetic homology but also in terms of biological homology.

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1 - University of Zurich, Institute of Systematic Botany, Zollikerstrasse 107, Zurich, 8008, Switzerland

Angiosperm flowers

Presentation Type: Symposium or Colloquium Presentation
Session: S4
Location: Room 4/Woodward
Date: Monday, July 28th, 2008
Time: 2:15 PM
Number: S4002
Abstract ID:344

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