Invasiveness Ranking System for Non-Native Plants of Alaska

Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 2Waterlilies reproduce through both seeds and rhizomes(Washington Department of Ecology 2005).Long-distance dispersal (0–3) 3Mature seeds are released into the water. The seeds are ableto float for a few days, by retaining air in the aril. Seeds aretransported to other areas and other lakes by water currents andducks that eat the seeds (Washington Department of Ecology2005, Schneider and Chaney 1981).Spread by humans (0–3) 2White waterlily is an extremely popular plant for cultivationin ornamental ponds. It has been intentionally introducedinto many lakes. Cultivars with color variations have beendeveloped and can be readily obtained at nurseries. (WashingtonDepartment of Ecology 2005).Allelopathic (0–2) 2Aqueous extracts from leaves, petioles, and rhizomes of whitewaterlily exhibit high allelopathy potential and are reported toinhibit seed germination and root growth of other aquatic plants(Quayyum et al. 1999, Spence 1998).Competitive Ability (0–3) 1No studies on competitive ability of Nymphaea odorata werefound. Since established white waterlily is able to dominate andreplace native macrphytes (Washington Department of Ecology2005), it is likely to outcompete other aquatic species.Thicket-forming//Smothering growth form (0–2) 2White waterlily forms dense floating mats of vegetation(Washington Department of Ecology 2005).Germination requirements (0–3) 0The seeds require light for germination. Seedlings are rarelyobserved in the field, when the adult population is high. However,a large number of seeds germinate after removal of adult plantswhen light breaks dormancy and stimulates germination(DiTomaso and Healy 2003, Else and Riemer 1984, Welker andRiemer 1982).Other invasive species in the genus (0–3) 3Nymphaea mexicana Zucc. is a noxious weed in California(DiTomaso and Healy 2003, USDA 2002).Aquatic, wetland or riparian species (0–3) 3White waterlily grows in shallow ponds, lakes, ditches, slowstreams, sloughs, and pools in marshes (Washington Departmentof Ecology 2005, Woods 2005, Wiersema 1997).Total for Biological Characteristics and Dispersal 18/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4White waterlily is a popular plant for cultivation in ornamentalponds. Many cultivars with color variations have been developed(Washington Department of Ecology 2005).Known level of impact in natural areas (0–6) 6A number of small lakes in Washington have been choked withwhite waterlily (Washington Department of Ecology 2005,City of Federal Way 2004). Alteration of water quality, nutrientdynamics, and plant and animal species composition has beendocumented for infested lakes (Frodge et al. 1995, Moore et al.1994).Role of anthropogenic and natural disturbance in3establishment (0–5)White waterlily has been introduced into lakes with various levelsof human disturbances (Washington Department of Ecology2005).Current global distribution (0–5) 0White waterlily is native to the eastern half of North America,including southern Canada. It has been introduced as anornamental in many parts of the world and it is expected toexpand its range. It is naturalized in South America (WashingtonDepartment of Ecology 2005, Woods 2005, Wiersema 1997).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)White waterlily distribution includes nearly all American statesand most Canadian provinces (Woods et al. 2005, USDA 2002,Wiersema 1997). Nymphaea odorata ssp. odorata is listed as anoxious weed in Washington (Invaders Database System 2003,USDA 2002).Total for Ecological Amplitude and Distribution 18/25Feasibility of ControlScoreSeed banks (0–3)UUnknownVegetative regeneration (0–3) 2White waterlily is able to resprout from rhizomes (WashingtonDepartment of Ecology, City of Federal Way 2004). Cuttingof rhizomes into 4 inches or larger pieces is recommended forpropagation in cultivation (Washington Department of Ecology2005).Level of effort required (0–4) 4White waterlily can be controlled by cutting, harvesting,covering with bottom barrier materials, and aquatic herbicides(City of Federal Way 2004, Washington Department of Ecology2005, Welker and Riemer 1982). Persistent picking of emergingleaves every other day during two to three growing seasonswill eventually kill the plants. After control treatments deadand decomposing leaves and rhizomes may form floating matsin the lake. Removing all dead materials from the water isrecommended. All control methods are time consuming andlabor intensive. There are no effective biological control agentsavailable at this time for waterlily (Washington Department ofEcology 2005).Total for Feasibility of Control 6/7Total score for 4 sections 78/97§5B-88