Invasive plants are not native to an area, can spread quickly and even cause economic or environmental harm — sometimes even threaten human health, the Pennsylvania Department of Conservation and Natural Resources reports.

Sometimes called as "exotic," "alien," "introduced," or "non-native" species, invasive plant infestations nationwide impact more than 100 million acres — or about the size of California, The Nature Conservancy reported.

The list of invasive plants in Pennsylvania includes 14 trees, 14 shrubs, 12 vines, 13 grasses, 27 herbs and 11 aquatic plants.

Local, regional and statewide groups that deal with invasive plants point to several varieties as being among the most pervasive in Southwestern Pennsylvania:

Multiflora rose

Introduced as ornamental rootstock from Japan in 1866, the Soil Conservation Service promoted its use in the 1930s for erosion control and livestock fencing. Recognition of its nearly unstoppable growth came too late, and it is now considered a noxious weed in many states.

Tree-of-heaven

Brought to Philadelphia in 1784 from China by an amateur gardener, this plant was the subject of Betty Smith's well-known book "A Tree Grows in Brooklyn." In addition to being invasive, tree-of-heaven stands are connected by underground roots, which produce a chemical preventing the establishment of other plant species nearby. It is often confused with native sumac, however tree-of-heaven leaves have a small gland on their underside.

Garlic mustard

First recorded in Long Island, N.Y., in 1868, garlic mustard is a cool-season biennial herb with triangular or heart-shaped leaves, which give off an odor of garlic. It is native to Europe but now ranges from eastern Canada south to Georgia and west to Oregon.

Mile-a-Minute

Growing up to 6 inches per day, mile-a-minute is a flowering vine first introduced to Eastern Pennsylvania in contaminated nursery stock from its native Philippines. It is covered with small, curved spines and produces green fruits that turn a metallic blue as the season goes on.

Source: Pennsylvania Department of Conservation and Natural Resources

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