Scientific name: Lythrum salicaria Purple loosestrife quickly establishes and spreads, outcompeting and replacing native grasses and other flowering plants that provide high quality food and habitat sources for wildlife. It forms dense stands that restrict native wetland plants and alters the structural and ecological values of wetlands. (Pennsylvania's Field Guide to Aquatic Invasive Species) Photo credit: © Rosane Miller / Flickr

Scientific name: Salvinia molesta This floating aquatic fern can form dense vegetation mats that reduce water-flow and lower light and oxygen levels in water. This stagnant dark environment negatively affects the biodiversity and abundance of freshwater species, including fish and submerged aquatic plants. Salvinia invasions can alter wetland ecosystems and cause wetland habitat loss. (ISSG.org) Photo credit: CC-BY-SA-3.0 via Wikimedia Commons

Scientific name: Senna alata The candlestick plant Invades forests, forest edges, humid ravines, riverbanks, woodlands and grasslands. It forms extensive root systems in its first year and competes for space and nutrients. Its large leaves shade out most native plants and it is known to be particularly aggressive in areas where there is a high water table. (NRCS) Photo credit: © Keith A. Bradley / Flickr