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Alligatorweed
(Alternanthera philoxeroides)
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Photo by "Slow Turning" on Flickr, used with permission
Oriental Bittersweet
(Celastrus orbiculatus)
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Species at a Glance
Oriental bittersweet, also called Asian bittersweet, is an aggressive, deciduous, woody vine that was introduced into the United States in the 1860s as an ornamental plant. Because of its colorful yellow and orange berries, it is still widely used as an ornamental vine, further promoting its spread.
Identification
Leaves: Glossy, rounded, elliptical or ovate, with finely toothed margins and an abruptly pointed tip. They are typically 5-13 cm (2-5.1 in) long and grow alternately and evenly around the stem.
Flowers: Female plants produce small clusters of greenish flowers along the stems in May and early June.
Fruits/Seeds: Globular capsules produced from July to October change from green to yellow as they ripen. At maturity the yellow capsules split open to reveal three red-orange, fleshy seed coatings, each containing 3-6 seeds. Male plants are non-fruiting.
Stems/Roots: Usually light brown, reaching 5-10 cm (2-3.9 in) in diameter and may be up to 18 m (60 ft) long.
Similar Species
American bittersweet (Celastrus scandens), a native species, can be distinguished from Oriental bittersweet because the flowers and fruits of the native plant grow only at the tips of small clusters of branches, rather than along long stretches of the stems. In addition, the fruit capsules ripen to a dark orange color.
Habitat
Oriental bittersweet infests forest edges, riparian corridors, woodlands, fields, hedge rows, coastal areas, and salt marsh edges, particularly those suffering from land disturbance. It prefers open, sunny sites but tolerates shade enough to invade forested areas. It will grow over anything it comes upon.
Spread
Oriental bittersweet reproduces prolifically by seeds, which are readily dispersed to new areas by birds. It also spreads through root suckering, which is when the plant forms a new growth-shoot from an existing exposed or buried root. Fruits can also float downstream to new areas. Vines with fruit have also been used ornamentally in wreaths and decorations.
Distribution
Native to Eastern Asia in Korea, China, and Japan, Oriental bittersweet has been reported as an invasive in 21 U.S. states including Pennsylvania, where it has been found in several counties spanning the state.
Note: Distribution data for this species may have changed since the publication of Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015), the source of information for this description.
Environmental Impacts
Oriental bittersweet grows vigorously, climbing over and smothering native vegetation and preventing sunlight from reaching native plants. Its weight on trees can lead to uprooting and blowover during high winds and heavy snowfalls.
In addition, Oriental bittersweet is displacing the native American bittersweet through competition and hybridization.
Video
Note
Information for this species profile comes from Pennsylvania's Field Guide to Aquatic Invasive Species (Second Edition 2015).