title: Geraniales flowers revisited: evolutionary trends in floral nectaries.
abstract: OBJECTIVE
  The detailed relationships in Geraniales in their current circumscription have only recently been clarified. The disparate floral morphologies and especially the nectaries of the corresponding group have consequently not previously been studied in a phylogenetic context.
  
  
  METHODS
  The present study investigates floral and especially nectary morphology and structure for representatives of 12 of the 13 currently accepted genera in the five families of the Geraniales. Flowers were studied using light microscopy and scanning electron microscopy.
  
  
  RESULTS
  The data demonstrate the derivation of even the most disparate floral morphologies from a basic pentamerous and pentacyclic organization, with an obdiplostemonous androecium and receptacular nectaries associated with the antesepalous stamens. Divergent morphologies are explained by modifications of merosity (tetramerous flowers), symmetry (several transitions to zygomorphic flowers) and elaboration of the nectaries into variously shaped outgrowths and appendages, especially in Francoaceae. The divergent development of nectar glands ultimately leads to either a reduction in their number (to one in some Geraniaceae and Melianthaceae) or their total loss (some Vivianiaceae).
  
  
  CONCLUSIONS
  Floral morphology of the Geraniales shows a high degree of similarity, despite the variation in overall floral appearance and nectary morphology. A hypothesis on the transformation of the nectaries within the Geraniales is presented.
authors.affiliation: Nees-Institut für Biodiversität der Pflanzen, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 170, D-53115 Bonn, Germany jjeiter@uni-bonn.de.|Biologie-Botanik, Freie Universität Berlin, Altensteinstraße 6, D-14195 Berlin, Germany.
authors.forename: Julius
authors.initials: J
authors.lastname: Jeiter
authors.affiliation: Nees-Institut für Biodiversität der Pflanzen, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 170, D-53115 Bonn, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Weigend
authors.affiliation: Biologie-Botanik, Freie Universität Berlin, Altensteinstraße 6, D-14195 Berlin, Germany.
authors.forename: Hartmut H
authors.initials: HH
authors.lastname: Hilger
mesh_terms: D035264:Flowers / Q000033:anatomy & histology* / Q000648:ultrastructure; D031314:Geraniaceae / Q000033:anatomy & histology / Q000235:genetics* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D057048:Plant Nectar / Q000235:genetics
chemical_list: D057048:Plant Nectar
keywords: Floral morphology; Francoaceae; Geraniaceae; Hypseocharitaceae; Melianthaceae; Vivianiaceae; floral anatomy; morphological transformation series; nectary