Sagittaria is a member of the water-plantain family of perennial, aquatic monocots. Sagittaria graminea is a large, widely distributed species found throughout the eastern half of the U.S. as far west as Wyoming and from Newfoundland to Florida in the East. Depending on the taxonomic treatment one reads, members of a group of 8 or 9 related taxa have, at one time or other, been considered varieties within S. graminea. These, along with two other related species, form the S. graminea complex. Based on the current accepted taxonomy, this complex consists of S. graminea var. graminea, S. g. var. weatherbiana, S. g. var. chapmanii, S. platyphylla, S. fasciculata, S. teres, S. isoetiformis, S. cristata,. S. rigida and S. secundifolia.

The taxonomic treatments of this complex have resulted in various taxonomic designations for the members. This is mainly because these treatments have been based on differences in inflorescences, bracts, submerged phyllodes, filaments, achenes and typical overall emerged leaf shape. However, many of these differences involve such fine structures, they are difficult to articulate, or the characteristics are so plastic, they are not very reliable as diagnostic features. Wooten has performed crossing studies to better determine the genetic relationship among these taxa. Our lab is expanding on this through genetic studies based on isozymes. Isozymes are used as genetic markers to determine relationships within and among populations and among taxa. So far we have looked at three taxa: S. g. graminea, S. g. chapmanii, and S. platyphylla. The genetic distance dendogram on the next page illustrates the results or our study so far:

These results seem to suggest that there is substantial genetic differentiation between S. g. graminea and S. platyphylla that is consistent with maintaining S. platyphylla as a separate species. Likewise, S. g. chapmanii is substantially differentiated from S. g. graminea to a somewhat greater degree than S. platyphylla suggesting that S. g. chapmanii should be given separate species status.

I would like to pursue this problem further by including some of the other taxa in the isozyme analysis. In particular, S. g. weatherbiana, S. isoetiformis, and more populations of the widespread, S. g. graminea.