Project Topic / Abstract:
“Pollen Wall Morphology in Cabomba caroliniana (Cabombaceae): An Ontogenetic Study”
The Cabombaceae is one of three plant families of waterlilies consisting of the two genera Brasenia and Cabomba. Cabomba caroliniana Gray is commonly known as fanwort and occurs in subtropical to temperate regions of eastern North and South America. This species is cultivated as a popular aquarium plant, but can also naturally occur as an aquatic weed choking off recreational and agricultural water ways. In addition to these economic factors, Cabomba, along with other waterliles, is of considerable evolutionary interest, because of its reputed position among the most primitive angiosperms. Particularly useful phylogenetic characters include pollen morphology and development. In this presentation, the ontogeny of both pollen grains and the pollen-producing organs, or anthers, are described using scanning electron, transmission electron, and light microscopy. Pollen was examined at stages progressing from undifferentiated sporogenous tissue to fully mature pollen grains. The ontogenetic timing of the following events were documented: differentiation of microspore mother cells, appearance of a callose wall, division into tetrads, formation of an aperture and apertural membrane, and formation of ectexine, endexine and intine. The development of an unusual series of microchannels throughout the ectexine was also evaluated. Regarding anther development, the concurrent ontogenetic features that were studied include: number and size of anther wall layers, appearance of endothecial thickenings, changes in tapetum morphology, and timing of tapetum dissociation. Significantly, an amoeboid type of tapetum was observed for the first time. Furthermore, this is the first study to utilize electron microscopy in an investigation of pollen development in either Cabomba or any other member of the family. The new ontogenetic data are discussed as they relate to phylogenetic interpretations of this important group of aquatic angiosperms.
- Taylor, M. L., B. L. Gutman, N. A. Melrose, A. M. Ingraham, J. A. Schwatz, and J. M. Osborn. 2008. Pollen and anther ontogeny in Cabomba caroliniana (Cabombaceae, Nymphaeales). American Journal of Botany 95:399-413. Article (PDF)
- National Conference on Undergraduate Research (Asheville, NC)
- Truman Undergraduate Research Symposium (Kirksville, MO)