Effect of Temperature on the Seed Germination of Garden Loosestrife (Lysimachia vulgaris L.)

Garden loosesrtife (Lysimachia vulgaris L.) is a highly invasive wetland plant species that is rapidly spreading in parts of western Washington. It is known to spread asexually through rhizomes, but the contribution of seed reproduction is largely unknown. We investigated seed germination under different temperature treatments, finding a strong effect. Seeds sown under summer conditions were able to germinate at high rates immediately. Seeds sown in spring/fall and winter conditions had low germination until moved into summer temperatures, when they germinated quickly at high rates. This facultative dormancy allows seeds to overwinter if germination conditions are not appropriate in the autumn, at the time of seed maturation. We suggest seed production should be eliminated to prevent further spread of the species.