Hybridization and Plasticity Contribute to Divergence Among Coastal and Wetland Populations of Invasive Hybrid Japanese Knotweed s.l. (Fallopia spp.)
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- Walls, R.L. Estuaries and Coasts (2010) 33: 902. doi:10.1007/s12237-009-9190-8
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Japanese knotweed s.l. (Fallopia spp.) is a highly invasive clonal plant, best known from roadside and riparian habitats. Its expansion into beaches on Long Island, NY, USA, represents a major habitat shift. I surveyed populations from beaches and wetlands and conducted a common garden experiment to test for variation in drought tolerance and phenotype among populations and habitats. All populations were composed mostly of first- and later-generation hybrids. I found significant variation among populations in growth, lamina size, specific leaf area (SLA), and biomass allocation, in both the field and the common garden. Lamina size, growth, and root-to-shoot responded plastically to drought treatment. Wetland populations tolerated drought as well as beach populations. Differentiation in SLA between habitats suggests that some selection for beach genotypes may have occurred. It appears that both hybridization and phenotypic plasticity are contributing to the expansion of Fallopia spp. into novel habitat.