Santa Fe River

It is too hard for me to tell what species of Sag it is. The leaves are very narrow and can get over one foot long. This is what it looked like in my aquarium:

I can't tell from the abstract on Vallisneria whether or not the authors have more than one Vallisneria species in the U.S. There ought to be. While on Tom Barr's Plantfest, 2004, I found an extremely large Vallisneria in the Ichetucknee River that, instead of sending up single female flowers on long, coiled, thin stems, sent up a thick stem with a node and a leaf at the end with several short flower stems coming from the node. Picture 1 is a drawing I made. Picture 2 is of the typical female flower.

Most interesting. I am not enough of a taxonomist to know if there is consistency the criteria that are used to define a genus or a species in botany. Ultimately, I think the criteria will be molecular differences and then taxonomists will then try to settle on some morphological differences that agree with the molecular data so that keys can be made so that you don't have to be a molecular biologist with a lot of time on your hands to key out a species. I find it interesting, that in the genus Ludwigia, flowers can have three to seven petals, or no petals at all. and leaves are usually opposite, but can be alternate or in a rosette. I guess we know one when we see one.

I know that molecular taxonomy has made some large revisions in animal taxonomy. For instance, the nematodes are now considered closely related to the arthropods, and the morphological character found to agree with the molecular data is that they both molt. Types of body cavities used to be important in distinguishing major groups (acoelomates, pseudocoelomates and those with 'true' coeloms formed in mesoderm), but are no longer important.

Hello Paul,
that's fine that You've got the Vall paper.
Species delimitation is really a difficult topic... especially in the often character-poor and morphologically plastic water plants.
As I understand it, really new in systematics is not simply the availability of molecular data but the consistent use of the principles of phylogenetic systematics (= cladistics) in the analysis of characters (molecular as well as morphological, ecological, behavioural etc.) and in the delimitation of taxonomic groups. Every grouping should be monophyletic, that means a natural group (a clade), descending from a last common ancestor that is not at the same time an ancestor of taxa outside the grouping. Often morphological and molecular characters are simultaneously analyzed. One of the advantages of molecular data is the potentially high amount of characters. There are mostly no a priori assumptions which characters are more important than others.The results of the analyses are testable hypotheses about the evolutionary history of the studied organisms, displayed as tree diagrams.