Greater morphological plasticity of exotic honeysuckle species may make them better invaders than native species

In a greenhouse experiment, we measured the morphological plasticity of two congeneric vines, Lonicera japonica Thunb., an important invasive species in the U.S. and L. sempervirens L., a non-invasive native. We hypothesized that greater morphological plasticity may contribute to the ability of L. japonica to occupy more habitat types, and contribute to its invasiveness. We compared the morphology of plants provided with climbing supports with plants that had no climbing supports, and thus quantified their morphological plasticity in response to an important variable in their habitats. The two species responded differently to the treatments, with L. japonica showing greater responses in more characters. For example, Lonicera japonica responded to climbing supports with a 15.3% decrease in internode length, a doubling of internode number and a 43% increase in shoot biomass. In contrast, climbing supports did not influence internode length or shoot biomass for L. sempervirens, and only resulted in a 25% increase in internode number. This plasticity may allow L. japonica to actively place plant modules in favorable microhabitats and ultimately affect plant fitness.