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Sean P. O’Neill

Project Topic / Abstract:

“A Comparative Light and Electron Microscopical Study of Anther and Pollen Morphology of the Podostemaceae”

The Podostemaceae is a tropical family of aquatic angiosperms that grow attached to rock substrates in freshwater streams and waterfalls. Due to their specialized habitat, plants exhibit several unusual features unique to the family. The majority of research conducted on the family has focused on documenting vegetative characteristics. Considerably less information is known about the reproductive morphology of the Podostemaceae. In particular, palynological data have primarily been gained from light microscopic analyses, and the pollen of only six species from Western India have been examined. In this presentation, pollen and anther morphology from four new-world genera are described using scanning electron and transmission electron microscopy, as well as light microscopy. The pollen of Marathrum, Oserya, Tristicha, and Vanroyenella is compared with regard to size, shape, surface ornamentation, aperture type and structure, and wall infrastructure. Regarding anther structure, the morphological characters examined include the following: number and size of anther wall layers, tapetum type, nature and density of endothecial thickenings, and extent of connective. These morphological data are discussed as they relate to evolutionary and taxonomic interpretations of the Podostemaceae. Significantly, pollen characters support classifications that segregate Tristicha from other members of the family. This is the first study to utilize electron microscopy in an evaluation of pollen morphology for any new-world taxa.


  • O’Neill, S. P., J. M. Osborn, C. T. Philbrick, and A. Novelo. 1997. Comparative pollen morphology of five New World genera of Podostemaceae. Aquatic Botany 57: 133-150. Article (PDF)
  • Osborn, J. M., S. P. O’Neill, and G. El-Ghazaly. 2000. Pollen morphology and ultrastructure of Marathrum schiedeanum (Podostemaceae).Grana 39: 221 -225. Article (PDF)



  • Truman Undergraduate Research Symposium (Kirksville, MO)


  • National Conference on Undergraduate Research (Schenectady, NY)
  • Tri-Beta Biological Honor Society Regional Meeting (Steelville, MO)
  • Truman Undergraduate Research Symposium (Kirksville, MO)