Graham, Shirley A. , Diazgranados, Mauricio , Barber, Janet C. .
Relationships among the confounding genera Ammannia, Hionanthera, Nesaea, and Rotala (Lythraceae).
The relationships and taxonomic limits of four morphologically similar herbaceous genera of the Lythraceae have long been poorly understood. Ammannia (ca. 25 spp.), Hionanthera (1-2 spp.), Nesaea (55-70 spp.), and Rotala (ca. 49 spp.) are small-flowered herbs of aquatic to amphibious habitats occurring in subtropical to tropical Africa and Asia, with a lesser presence in the New World. An inadequate knowledge of features regarded as diagnostic of the genera, together with their similar habit and floral structure, have resulted in diverse generic and infrageneric delineations and multiple species transfers among Ammannia, Nesaea, and Rotala. The taxonomic difficulties may be due to phenomena such as hybridization, selfing within localized populations, or heterostyly, the latter of which may have led to different floral morphs being described as different species. In this study, vegetative, anatomical, floral, seed, and pollen characters are compared and new chromosome numbers are reported for Ammannia and Nesaea. Phylogenetic relationships of the genera are hypothesized based on data sets from ITS, rbcL and trnL-F gene regions. Ammannia, Hionanthera, and Nesaea unite as a monophyly (A/H/N clade) in which Ammannia and Nesaea are paraphyletic and the mono- or ditypic Hionanthera is sister to different species of Nesaea, depending on the analysis. Total morphological and molecular evidence supports congeneric status for Ammannia, Hionanthera, and Nesaea under the earliest name, Ammannia. Rotala is found to form an early lineage of the family with the American genera Heimia and Didiplis and is only distantly related to the other three genera. Significantly, with respect to the traditional reliance on morphological characters in determining relationships, Rotala exhibits the the same synapomorphies as the A/H/N clade. Our molecular evidence, however, reveals an instance in which morphological convergence has occurred to an exceptional degree in plants living in the specialized environment of fluctuating water levels.
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1 - Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri, 63166-0299, USA
2 - Saint Louis University, Department of Biology, 3507 Laclede Ave., Macelwane Lab 231, St. Louis, Missouri, 63103-2010, United States of America
3 - Saint Louis University, Department of Biology, 3507 Laclede Avenue, St Louis, Missouri, 63103-2010, USA
Presentation Type: Poster:Posters for Sections
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM