title: Pollen structure and function in caesalpinioid legumes.
abstract: OBJECTIVE
  A diverse range of pollen morphologies occurs within the large, paraphyletic legume subfamily Caesalpinioideae, especially among early-branching lineages. Previous studies have hypothesized an association between surface ornamentation and pollination syndrome or other aspects of pollen function such as desiccation tolerance and adaptations to accommodate volume changes.
  
  
  METHODS
  We reviewed caesalpinioid pollen morphology using light microscopy, scanning and transmission electron microscopy, in combination with a literature survey of pollination vectors.
  
  
  RESULTS
  Pollen structural diversity is greatest in the early-branching tribes Cercideae and Detarieae, whereas Cassieae and Caesalpinieae are relatively low in pollen diversity. Functional structures to counter desiccation include opercula (lids) covering apertures and reduced aperture size. Structures preventing wall rupture during dehydration and rehydration include different forms of colpi (syncolpi, parasyncolpi, pseudocolpi), striate supratectal ornamentation, and columellate or granular wall structures that resist tensile or compressive forces respectively. Specialized aperture structures (Zwischenkörper) may be advantageous for efficient germination of the pollen tube.
  
  
  CONCLUSIONS
  In Detarieae and Cercideae in particular, there is potential to utilize pollen characters to estimate pollination systems where these are unknown. Supratectal verrucae and gemmae have apparently evolved iteratively in Cercideae and Detarieae. At the species level, there is a potential correlation between striate/verrucate patterns and vertebrate pollination.
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK h.banks@kew.org.
authors.forename: Hannah
authors.initials: H
authors.lastname: Banks
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK.
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Rudall
mesh_terms: D000818:Animals; D029911:Caesalpinia / Q000033:anatomy & histology* / Q000502:physiology* / Q000648:ultrastructure; D018525:Germination; D010802:Phylogeny; D011058:Pollen / Q000033:anatomy & histology* / Q000502:physiology* / Q000648:ultrastructure; D054817:Pollination
keywords: Caesalpinoideae; Leguminosae; exine morphology; pollen germination; pollen structure; pollination syndromes