title: Successive cambia: a developmental oddity or an adaptive structure?
abstract: BACKGROUND
  Secondary growth by successive cambia is a rare phenomenon in woody plant species. Only few plant species, within different phylogenetic clades, have secondary growth by more than one vascular cambium. Often, these successive cambia are organised concentrically. In the mangrove genus Avicennia however, the successive cambia seem to have a more complex organisation. This study aimed (i) at understanding the development of successive cambia by giving a three-dimensional description of the hydraulic architecture of Avicennia and (ii) at unveiling the possible adaptive nature of growth by successive cambia through a study of the ecological distribution of plant species with concentric internal phloem.
  
  
  RESULTS
  Avicennia had a complex network of non-cylindrical wood patches, the complexity of which increased with more stressful ecological conditions. As internal phloem has been suggested to play a role in water storage and embolism repair, the spatial organisation of Avicennia wood could provide advantages in the ecologically stressful conditions species of this mangrove genus are growing in. Furthermore, we could observe that 84.9% of the woody shrub and tree species with concentric internal phloem occurred in either dry or saline environments strengthening the hypothesis that successive cambia provide the necessary advantages for survival in harsh environmental conditions.
  
  
  CONCLUSIONS
  Successive cambia are an ecologically important characteristic, which seems strongly related with water-limited environments.
authors.affiliation: Laboratory for Plant Biology and Nature Management, APNA, Vrije Universiteit Brussel, VUB, Brussels, Belgium. erobert@vub.ac.be
authors.forename: Elisabeth M R
authors.initials: EM
authors.lastname: Robert
authors.forename: Nele
authors.initials: N
authors.lastname: Schmitz
authors.forename: Ilse
authors.initials: I
authors.lastname: Boeren
authors.forename: Tess
authors.initials: T
authors.lastname: Driessens
authors.forename: Kristof
authors.initials: K
authors.lastname: Herremans
authors.forename: Johan
authors.initials: J
authors.lastname: De Mey
authors.forename: Elke
authors.initials: E
authors.lastname: Van de Casteele
authors.forename: Hans
authors.initials: H
authors.lastname: Beeckman
authors.forename: Nico
authors.initials: N
authors.lastname: Koedam
mesh_terms: D000222:Adaptation, Physiological; D032407:Avicennia / Q000033:anatomy & histology; D058506:Cambium / Q000254:growth & development*; D017753:Ecosystem; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water