Japanese Stiltgrass
Japanese stiltgrass is an annual grass that sprawls along the ground as it grows. The leaves are pale green, narrow, and lance-shaped with a distinctive silvery stripe of hairs along the midrib. Tiny flowers are produced on slender stalks in late summer.
Yellow Iris
Yellow iris is an herbaceous perennial that can grow between 3-4 feet. The broad, lance shaped leaves are stiff and erect. The yellow, showy flowers bloom from April to June.
Wild Parsnip
Wild parsnip is a biennial herb that grows to 2-5 feet. Alternate, compound, branched leaves have serrated edges. First year rosettes have pinnately compound leaves. Adult plants bloom June through August with small, five-petaled, yellow flowers arranged in a flat-topped, broad umbel 2-6 inches.
Swallow-worts
Black and pale swallow-worts are herbaceous, perennial, twining vines. Leaves are opposite and glossy. Small maroon to pale pink flowers are present in late May through late July. Seed pods are smooth, slender, and pointed and are abundant in late summer. Pods split open, releasing innumerable downy seeds that are easily carried miles by wind.
Purple Loosestrife
Purple loosestrife is an erect, herbaceous perennial that grows 3-7 feet. It is easily identified by its showy, magenta flowers from July to September. Linear shaped leaves grow oppositely along square stems. This aggressive plant spreads both vegetatively and by abundant seed dispersal.
Oriental Bittersweet
Oriental, or Asiatic, bittersweet is a perennial, deciduous vine that can grow to 60 feet. Stems have dark brown, striated bark. Elliptic to ovate leaves are alternate and spiral evenly around the stem. Axillary flowers bloom in May to early June yielding bright, reddish-orange fruit in the fall. Oriental bittersweet can be confused with American bittersweet, which has a terminal inflorescence and is native.
Garlic Mustard
Garlic mustard is a biennial herb and grows as a rosette of kidney shaped leaves in the first year. The second-year plant can grow multiple stems up to four feet with triangular, sharply-toothed leaves. In May, four-petaled, white flowers grow in clusters at the top of the stem. Garlic mustard produces a multitude of seeds, which can remain viable for seven years or more.
Japanese Knotweed
Japanese knotweed is a fast-growing, herbaceous perennial with jointed, hollow stems and alternate, leathery leaves that are broadly ovate. A cascade of white flowers blooms in August, and dormant reddish stems are visible in winter. Giant knotweed, Fallopia sachalinensis, is another nonnative knotweed in the Park.
Giant Hogweed
Giant hogweed is a biennial herb that grows to 8-14 feet. Plants sprout in early spring from forked taproots or seeds. Stems are hollow, and leaves are lobed. The best time to identify giant hogweed is when it is in bloom in June.
