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Systematics Section / ASPT

Les, Donald H. [1], Moody, Michael L. [2], Jacobs, Surrey [3].

Systematics of Vallisneria L. (Hydrocharitaceae): Australia and beyond.

The aquatic genus Vallisneria, with its familiar rosettes of submersed, ribbonlike leaves and unusual surface pollination mechanism, is poorly understood with respect to its global diversity and taxonomic delimitation of species. Contemporary estimates vary from one to ten species worldwide; however, previous studies of the genus have not approached the question from a global perspective and have been inconclusive. Another issue concerns the taxonomic status of Maidenia, a monotypic Australian genus quite similar to Vallisneria. We have undertaken an intensive study of Vallisneria in Australia where relatively high diversity is indicated. Australia is the only region containing caulescent forms of Vallisneria where leaves are borne on an elongate stem rather than in rosettes. Two Vallisneria species (V. caulescens, V. triptera) as well as Maidenia rubra are caulescent. The outgroup Nechamandra (clearly indicated as sister to Vallisneria by combined morphological and molecular data) also is caulescent. The remaining rosulate taxa are difficult to distinguish; yet, despite exhibiting differences in size and duration (annual or perennial), they often are treated as variants of species (e.g., V. americana; V. spiralis) assumed to possess relatively widespread distributions. We conducted phylogenetic analyses of Vallisneria material collected throughout Australia, Asia and North America using DNA sequence data from nuclear (nrITS) and plastid (trnK intron) genomes. Our results reveal considerably higher diversity in Vallisneria (11-13 species) than has been presumed. Other important findings include: 1) the nesting of "Maidenia" within Vallisneria (associated with other caulescent taxa), 2) the distinctness of V. americana, V. asiatica, V. gigantea, V. nana and V. natans, and 3) a clade comprising V. gracilis, V. annua, and several previously undescribed taxa. Molecular data also support the recognition of two, distinct, indigenous North American species and reveal the introduction of V. natans, a nonindigenous species previously unknown to North America.

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1 - University of Connecticut, Department of Ecology & Evolutionary Biology, 75 North Eagleville Rd. U-3043, Storrs, Connecticut, 06269-3043, USA
2 - Indiana University, Department of Biology, Jordan Hall, 1001 East Third Street, Bloomington, Indiana, 47405, USA
3 - Royal Botanic Gardens, Mrs Macquaries Road, Sydney, New South Wales, 2000, Australia

molecular systematics
Australian flora.

Presentation Type: Oral Paper
Session: 3-2
Location: Salon J - Austin Grand Ballroom/Hilton
Date: Monday, August 15th, 2005
Time: 8:30 AM
Abstract ID:155

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