Grewell, Brenda J. , Canington, Deborah , Futrell, Caryn J. .
Cytologic and morphometric analyses clarify Ludwigia species invading aquatic ecosystems in Pacific western states, USA.
Recent aggressive spread of Ludwigia species (Onagraceae) has impacted both sensitive wetlands and water canals in Pacific western states. These aquatic weeds can rapidly form dense floating mats that displace native vegetation and open water habitat, degrade water quality, increase flood risk, and inhibit effective mosquito control. Variable growth responses to environmental conditions and contradictory taxonomic keys have complicated accurate species identifications that are essential for understanding invasive weed ecology and management. We present cytological and morphometric data that confirm the presence of four different taxa of Ludwigia (sect. Oligospermum) in the region, while previously only three taxa were recognized. Mitotic chromosome number determinations were made from 61 populations. Diploid (2n = 16), hexaploid (2n = 48), and decaploid (2n = 80) strains were detected. Multivariate analysis of 26 quantitative morphological characters from fresh specimens of 473 individuals and 29 populations support the recognition of four taxa. A cluster analysis differentiated L. hexapetala (decaploid), L. grandiflora (hexaploid), L. peploides ssp. peploides, and L. p. ssp. montevidensis (diploid) as four morphologically distinct groups. Discriminant analyses were performed that confirmed unique morphological characteristics among ploidy levels and species groups. Reproductive characters are essential for identification. Our analyses show that L. hexapetala is a prevalent invasive Ludwigia species in the region and support revision of the current taxonomic key for this species. We also present confirmation and the first report of the presence of exotic L. grandiflora (South American origin) in California.
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1 - USDA-ARS Exotic & Invasive Weeds Research, Department of Plant Sciences MS-4, University of California, Davis, 1 Shields Avenue, Davis, California, 95616, USA
2 - University of California Davis, Section of Plant Biology, One Shields Avenue, Davis, California, 95616-8537, USA
3 - USDA-ARS Exotic & Invasive Weeds Research, Aquatic Weed Laboratory, University of California Davis, 2705 Levee Road, Davis, CA, 95616, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Council Chambers/SUB
Date: Monday, July 28th, 2008
Time: 10:45 AM