Journal Article

Synorganisation without organ fusion in the flowers of <i>Geranium robertianum</i> (Geraniaceae) and its not so trivial obdiplostemony

Peter K. Endress

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 106, issue 5, pages 687-695
Published in print November 2010 | ISSN: 0305-7364
Published online August 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq171
Synorganisation without organ fusion in the flowers of Geranium robertianum (Geraniaceae) and its not so trivial obdiplostemony

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Synorganisation of floral organs, an important means in angiosperm flower evolution, is mostly realized by congenital or post-genital organ fusion. Intimate synorganisation of many floral organs without fusion, as present in Geranium robertianum, is poorly known and needs to be studied. Obdiplostemony, the seemingly reversed position of two stamen whorls, widely distributed in core eudicots, has been the subject of much attention, but there is confusion in the literature. Obdiplostemony occurs in Geranium and whether and how it is involved in this synorganisation is explored here.

Methods

Floral development and architecture were studied with light microscopy based on microtome section series and with scanning electron microscopy.

Key Results

Intimate synorganisation of floral organs is effected by the formation of five separate nectar canals for the proboscis of pollinators. Each nectar canal is formed by six adjacent organs from four organ whorls. In addition, the sepals are hooked together by the formation of longitudinal ribs and grooves, and provide a firm scaffold for the canals. Obdiplostemony provides a guide rail within each canal formed by the flanks of the antepetalous stamen filaments.

Conclusions

Intimate synorganisation in flowers can be realized without any fusion, and obdiplostemony may play a role in this synorganisation.

Keywords: Angiosperms; diplostemony; floral architecture; floral development; floral morphology; fusion; Geraniaceae; Geranium robertianum; obdiplostemony; synorganisation

Journal Article.  6038 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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