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Alligatorweed
(Alternanthera philoxeroides)
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Photo credit: © Udo Schmidt, https://flic.kr/p/cGoZC
Policeman's Helmet
(Impatiens glandulifera)
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Species at a Glance
Policeman’s helmet, also called ornamental jewelweed and poor man’s orchid, is a large, annual, herbaceous plant in the “touch-me-not” family that grows up 3 m (10 ft) tall. The large pink-purple flowers are shaped like an English policeman’s helmet or an orchid, giving the plant its common name.
Identification
Leaves: Large oblong or egg-shaped leaves are toothed with a pointed tip. They are either oppositely arranged or found whorled in groups of three.
Flowers: Irregular five-parted flowers arise from the leaf axils and are pink to white to purple in color. Flowering occurs from mid-June through October.
Fruits/Seeds: Seeds can eject up to 20 feet from mature seed pods when touched or disturbed. They remain viable in the soil for 12-18 months.
Stems/Roots: Fleshy, smooth, hollow, reddish stems are multi-branching and resemble bamboo. They have distinct swollen nodes that help distinguish it from other plants.
Similar Species
Policeman’s helmet could be mistaken for other members of the same genus such as orange jewelweed (Impatiens capensis) and the pale touch-me-not (Impatiens pallida). It can be distinguished from these look-a-likes by its pinkish-purple flowers, swollen nodes, and serrated leaves.
Habitat
Although it is tolerant of many soil types, policeman’s helmet must have high moisture content such as the soils found in wetlands, riparian areas, moist woodlands, gardens, and parks. It tends to thrive in partial shade, but can also be found growing in full sun.
Spread
Reproducing entirely by seeds, policeman’s helmet can produce up to 800 seeds per plant that have long viability and high germination rates. Seeds can float and germinate in the water, allowing the plant to move down waterways into new areas.
Distribution
Native to the western Himalayas, policeman’s helmet was probably introduced into the United States as a garden ornamental. In Britain, it is considered extremely invasive and is one of the “top 20” non-native weeds. In the Mid-Atlantic region, this species is found in New York.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Environmental Impacts
Policeman’s helmet is a highly aggressive invader that forms dense colonies that displace native and beneficial plants, reduce forest regeneration, and contribute to flooding and erosion by changing or stopping water movement. Because it is an annual, it dies down in the winter, leaving no food or habitat for wildlife.
Video
Note
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).