Les, Donald .
Nonindigenous North American Najas - new nuances on noxious naiad nativity.
North America contains eight of the approximately 40 species recognized within the cosmopolitan aquatic genus Najas (Hydrocharitaceae). Weedy and invasive characteristics have been ascribed to both the native and non-native species. However, the indigenous status of some species has been questioned. Using molecular analysis of samples covering all North American taxa and many accessions from other areas, we have determined the geographical origin for most of the non-native introductions. Genetic analysis of historical herbarium records allowed us to ascertain that Najas graminea was introduced to California in the 1940s from Asia, most likely as a consequence of rice (Oryza) culture. It is doubtful that N. graminea has persisted in the region as it has not been verified there since 1991. Our investigations revealed further that several recently collected California specimens attributed to N. graminea were misidentified and actually represent material of the morphologically similar N. gracillima. Furthermore, our analyses indicated that these West Coast populations of N. gracillima also were introduced from Asia and are distinct genetically from the native Eastern North American populations. Similarly, we have been able to trace back to Eurasia the origin of the first North American introduction of the non-indigenous N. minor, although the dispersal of this species through prolonged rice culture in the Old World makes it difficult to pinpoint the precise source for North American plants. We also documented a second introduction of N. minor to North America, for which the geographical origin remains uncertain. Although this lineage is associated mainly with the New England region, scattered, highly disjunct localities (as remote as California) indicate recurrent introductions over the past century. The native North American N. guadalupensis represents a special case, where improper subspecies delimitation has made it difficult to evaluate nativity in any given subregion. Some weedy populations resembling N. guadalupensis have arisen as a consequence of interspecific hybridization with the closely related and also indigenous N. flexilis. Finally, although some authors regard N. filifolia as a range extension of the South American N. conferta, it differs genetically from all South American Najas material examined to date, supporting its status as indigenous. In highly reduced aquatic plants such as Najas, the application of genetic information is essential to trace the distribution and origin of the various taxa with accuracy.
Log in to add this item to your schedule
1 - University Of Connecticut, Department Of Ecology & Evolutionary Biology, 75 N. Eagleville Road, Unit 3043, Storrs, CT, 06269-3043, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Franklin B/Hyatt
Date: Monday, July 9th, 2012
Time: 9:00 AM