| A review of the vectors by which non-native plants are transferred from their native habitat to new regions of the world revealed that the majority of plant introductions are intentional. Many of the most common invasive plants have been traced to multiple vectors, with at least one intentional vector per species.; While much research has been done on the introduction of non-native plants into the US that began with European colonization of America, little information is available regarding the flow of American species into Europe. A database of 6000 plant species native to America was categorized as invasive, naturalized, escaping, or benign in Europe. Analysis revealed a positive relationship between the number of vectors of introduction and the likelihood of a species being non-benign (invasive, naturalized or escaping). Certain plant families were found to have more non-benign species than others. Non-benign species were more likely to originate from North America, and a species weedy in its native range was much more likely to be non-benign in Europe. A warning list of species likely to become invasive, based on this analysis, is included.; Fallopia japonica (Japanese knotweed), an Asian plant invasive in North America and Europe, has been the focus of very little research in the US. Investigation of this species revealed that it has a subdioecious breeding system, with sex determination likely to be under genetic control. Field studies and germination experiments show that this species, known for its vegetative reproduction, produces vast amounts of viable seed and seedlings that survive in the wild. Wild F. japonica can cross with cultivars available for sale in the nursery industry, and the cultivars also produce viable seed.; Fallopia japonica can also hybridize with the less common F. sachalinensis (giant knotweed) and F. baldschuanica (silver lace vine), other Asian species introduced to the US. A study using leaf morphology, leaf trichomes, and ploidy level analysis by flow cytometry indicated that hybrids between F. japonica and F. sachalinensis do exist in the US, but are rare. There is also a range of DNA content within species, including octoploid and tetraploid F. japonica. |
