RICHMOND, Va. (WRIC) -- The Virginia Department of Conservation and Recreation (DCR) announced on Tuesday that 13 species have been added to the Virginia Invasive Plant Species List. The list -- which now includes up to 103 different species -- consists of plants that have been determined by DCR to threaten Virginia's ecosystems, more specifically marshes, wetlands, forests and waterways. Two-horned trapa (Trapa bispinosa) (Courtesy of Department of Conservation and Recreation.) An invasive species, as defined by DCR, is a non-native species that actively causes harm or could potentially cause harm to natural resources and humans as well as economic activity. The following species have been added, ranked by their invasiveness level: Virginia Invasiveness Rank: High Chinese tallow-tree (Triadica sebifera)  Floating primrose-willow (Ludwigia peploides var. glabrescens)  Italian arum (Arum italicum)  Ravenna-grass (Tripidium ravennae)  Trifoliate orange (Citrus trifoliata)  Two-horned trapa (Trapa bispinosa var. iinumai)  Virginia Invasiveness Rank: Medium Curled pondweed (Potamogeton crispus)  Fountain grass (Cenchrus purpurascens)  Incised fumewort (Corydalis incisa)  Leatherleaf mahonia (Mahonia bealei)  Sweet autumn clematis (Clematis terniflora) Virginia Invasiveness Rank: Low Nandina (Nandina domestica) Orange-eye butterfly-bush (Buddleja davidii)  Nandina (Nandina domestica), (Courtesy of Department of Conservation and Recreation) According to DCR, there are several factors considered when deciding what plants will be added to the list -- including how readily seeds are spread through a landscape and whether or not Virginia contains suitable habitats for the species. While the list has no regulatory authority, according to DCR, it serves educational purposes and is updated regularly. For more information on how the ranks are determined and to view the full list with photos, click here. DCR's website provides a free online tool that people can use to search for native species to plant instead of invasive species -- the Virginia Native Plant Finder. If you or someone you know wants to report a sighting of an invasive plant in Virginia, click here.