Roadside invader: The higher the traffic, the easier the invasive common ragweed disperses. Common ragweed is an annual plant whose allergenic pollen affects human health. It's an invasive species particularly well-adapted to living at roadsides. New research found high population growth along high-traffic roads even in shaded and less disturbed road sections, suggesting that seed dispersal by vehicles and by road maintenance can compensate, at least partly, for less favorable habitat conditions. Source 1p.