title: Aerodynamics and pollen ultrastructure in Ephedra.
abstract: •
  
  
  OBJECTIVE
  Pollen dispersal is affected by the terminal settling velocity (Ut) of the grains, which is determined by their size, bulk density, and by atmospheric conditions. The likelihood that wind-dispersed pollen is captured by ovulate organs is influenced by the aerodynamic environment created around and by ovulate organs. We investigated pollen ultrastructure and Ut of Ephedra foeminea (purported to be entomophilous), and simulated the capture efficiency of its ovules. Results were compared with those from previously studied anemophilous Ephedra species.•
  
  
  METHODS
  Ut was determined using stroboscopic photography of pollen in free fall. The acceleration field around an "average" ovule was calculated, and inflight behavior of pollen grains was predicted using computer simulations. Pollen morphology and ultrastructure were investigated using SEM and STEM.•
  
  
  RESULTS
  Pollen wall ultrastructure was correlated with Ut in Ephedra. The relative proportion and amount of granules in the infratectum determine pollen bulk densities, and (together with overall size) determine Ut and thus dispersal capability. Computer simulations failed to reveal any functional traits favoring anemophilous pollen capture in E. foeminea.•
  
  
  CONCLUSIONS
  The fast Ut and dense ultrastructure of E. foeminea pollen are consistent with functional traits that distinguish entomophilous species from anemophilous species. In anemophilous Ephedra species, ovulate organs create an aerodynamic microenvironment that directs airborne pollen to the pollination drops. In E. foeminea, no such microenvironment is created. Ephedroid palynomorphs from the Cretaceous share the ultrastructural characteristics of E. foeminea, and at least some may, therefore, have been produced by insect-pollinated plants.
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, SE-106 91, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Bolinder
authors.affiliation: Section of Plant Biology, School of Integrative Plant Science, Cornell University, Ithaca, New York 14853 USA.
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Niklas
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, SE-106 91, Sweden.
authors.forename: Catarina
authors.initials: C
authors.lastname: Rydin
mesh_terms: D002473:Cell Wall / Q000648:ultrastructure; D029789:Ephedra / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D017348:Microscopy, Electron, Scanning Transmission; D011058:Pollen / Q000502:physiology* / Q000648:ultrastructure; D054817:Pollination; D014919:Wind
keywords: Gnetales; Welwitschia; anemophily; entomophily; granular infratectum; pollen morphology; pollination; scanning electron microscopy; scanning transmission electron microscopy