Systematics/Phytogeography / Taxonomie/ Section
Les, Donald H. , Sheldon, Sallie , Tippery, Nicholas P. .
Systematics of Najas (Hydrocharitaceae).
Najas L. (Hydrocharitaceae) is a submersed, hydrophilous genus of about 32 species distributed worldwide. Two subgenera are recognized: Caulinia (monoecious) and Najas (dioecious; monotypic). Like other submersed aquatics, Najas species are extensively reduced. They are particularly difficult to identify in the absence of seeds, which provide the most useful patterns of taxonomic variation; however, seeds usually are present due to the annual habit. Najas has undergone several recent revisions; however, contemporary authors have all but abandoned classification below the subgenus level (which segregates only a single species) citing inconsistency in delimiting characters. In particular, the sectional limits proposed by Rendle in the 19th century have been dismissed, even though a detailed phylogenetic analysis of the genus has never been undertaken. Our phylogenetic study of Najas will evaluate not only the current taxonomy of the genus, but also will assess whether there are clades that merit taxonomic recognition at the sectional level. This work focuses on the North American representatives, which comprise eight species and four subspecies. The status of N. guadalupensis in the northeastern United States has been especially difficult to determine. Here the species has been regarded both as imperiled and nonindigenous and populations characteristically lack seeds. Phylogenetic analysis of 10 taxa (7 North American) was conducted using combined cpDNA and nrDNA sequence data. Our results: 1) corroborate the distinctness of the subgenera; 2) resolve a New World clade corresponding with Rendle’s section Americanae; 3) resolve an Australian/Eurasian clade corresponding with Rendle’s section Euvaginatae; and 4) indicate that N. guadalupensis is a highly complex taxon requiring further evaluation. North American Najas species exhibit interesting phylogenetic affinities to Asia, Australia, Europe and South America. Although further taxon sampling is necessary, our preliminary results indicate that Rendle’s sectional classification should be reevaluated as reliable phylogenetic information becomes available.
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1 - University of Connecticut, Ecology & Evolutionary Biology, 75 North Eagleville Road, U-3043, Storrs, Connecticut, 062693043, USA
2 - Middlebury College, Department of Biology, Middlebury, Vermont, 05753, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 1:00 PM