title: Floral structure of Emmotum (Icacinaceae sensu stricto or Emmotaceae), a phylogenetically isolated genus of lamiids with a unique pseudotrimerous gynoecium, bitegmic ovules and monosporangiate thecae.
abstract: OBJECTIVE
  Icacinaceae sensu stricto consist of a group of early branching lineages of lamiids whose relationships are not yet resolved and whose detailed floral morphology is poorly known. The most bizarre flowers occur in Emmotum: the gynoecium has three locules on one side and none on the other. It has been interpreted as consisting of three fertile and two sterile carpels or of one fertile carpel with two longitudinal septa and two sterile carpels. This study focused primarily on the outer and inner morphology of the gynoecium to resolve its disputed structure, and ovule structure was also studied. In addition, the perianth and androecium were investigated.
  
  
  METHODS
  Flowers and floral buds of two Emmotum species, E. harleyi and E. nitens, were collected and fixed in the field, and then studied by scanning electron microscopy. Microtome section series were used to reconstruct their morphology.
  
  
  RESULTS
  The gynoecium in Emmotum was confirmed as pentamerous, consisting of three fertile and two sterile carpels. Each of the three locules behaves as the single locule in other Icacinaceae, with the placenta of the two ovules being identical, which shows that three fertile carpels are present. In addition, it was found that the ovules are bitegmic, which is almost unique in lamiids, and that the stamens have monosporangiate thecae, which also occurs in the closely related family Oncothecaceae, but is not known from any other Icacinaceae sensu lato so far.
  
  
  CONCLUSIONS
  The flowers of Emmotum have unique characters at different evolutionary levels: the pseudotrimerous gynoecium at angiosperm level, the bitegmic ovules at lamiid level and the monosporangiate thecae at family or family group level. However, in general, the floral morphology of Emmotum fits well in Icacinaceae. More comparative research on flower structure is necessary in Icacinaceae and other early branching lineages of lamiids to better understand the initial evolution of this large lineage of asterids.
authors.affiliation: Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland pendress@systbot.uzh.ch.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Endress
authors.affiliation: Departamento de Ciências Biologicas, Universidade Estadual de Feira de Santana, Av. Universitária s/n, CEP 44036-900, Feira de Santana, Bahia, Brazil.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rapini
mesh_terms: D005075:Biological Evolution; D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000235:genetics; D008855:Microscopy, Electron, Scanning; D056771:Ovule / Q000033:anatomy & histology / Q000235:genetics; D010802:Phylogeny
keywords: Asterids; E. nitens; Emmotaceae; Emmotum harleyi; Garryales; Icacinaceae; anthers; early branching lamiids; floral morphology; gynoecium; ovules