Oriental bittersweet (Celastrus orbiculatus)
Celastrus orbiculata Thunb., orth. var.
CONFIRMATION STATUS: Confirmed.
TAXONOMY: The current scientific name of Oriental bittersweet is
Celastrus orbiculatus Thunb. Prior to Oriental bittersweet's introduction,
American bittersweet (Celastrus scandens) was the only North American
representative of the stafftree family north of Mexico. Oriental and
American bittersweet have the potential to hybridize. Although the cur-
rent extent of Oriental bittersweet × American bittersweet hybridization
in the wild is unknown, the 2 bittersweets are cross-fertile in the labora-
tory. Hybrids are not widely reported in the field; however, this may be
due to the difficulty in identifying bittersweet hybrids. Genetic studies of
field specimens are needed to determine levels of hybridization and intro-
gression between Oriental bittersweet and American bittersweet.
NATIVE STATUS: Introduced, United States and Canada.
GENERAL BOTANICAL CHARACTERISTICS: Oriental bittersweet
is a deciduous liana. The stems are woody and twining. They may reach 66
feet (20 m) in length and 4 inches (10 cm) in width, depending upon stem
age and supporting vegetation. The leaves are alternate, oblong, 2 to 5
inches (4-12 cm) long, and 1.4 to 2.0 inches (3.5-5.1 cm) wide. Leaf morph-
ology is highly variable, with Oriental bittersweet showing reduced leaf
mass per unit leaf area and increased leaf area in shade. Oriental bitter-
sweet is functionally dioecious. Flowers are sparse, occurring in 3-flower-
ed, axillary cymes. Fruits develop next to the vegetative buds. Outer
vegetative bud scales may be spiny. A typical plant bears upwards of 370
fruits/year. Fruits are dehiscent, 3-valved capsules about 0.4 inch (1 cm)
in diameter. The capsules are relatively large and deciduous. Each valve
contains 1 or 2 seeds covered by fleshy, yellowish-red arils. In Japan, mean
sizes of 3.8 mm in seed length, 0.023 mm in seed width, and 7.5 mm in
capsule length. Similar capsule sizes occur on plants in the United States
(range: 1.5-1.6 mm in width; 6-8 mm in diameter). Oriental bittersweet
roots are deep and spreading. They may be as much as 0.8 inch (2.0 cm)
thick and reach deeper than roots of surrounding plant species.
Oriental bittersweet's growth habit is climbing and/or sprawling. It uses
woody shrubs and/or trees for structural support, intertwining its branches
around support trunks and branches. Branches may eventually overtop or
shade out supporting plants. In Rock Creek Park, Washington DC, Oriental
bittersweet used other bole-climbing lianas and vines including Virginia
creeper (Parthenocissus quinquefolia), poison-ivy, and English ivy (Hedera
helix) for initial structural support. After twining around these lianas, Ori-
ental bittersweet branches grew into and twined around tree crowns. This
climbing habit enabled Oriental bittersweet to grow above other lianas and
access the tops of the largest trees in the Park. Oriental bittersweet
assumes a sprawling form on open sites and sprawling Oriental bitter-
sweet branches may form impenetrable thickets.
REGENERATION PROCESS: Oriental bittersweet regenerates by
sprouting and from seed. Its invasiveness is due, in part, to its superior
ability to establish from both sprouts and seeds compared to most native
lianas and other associated native woody species. Based on Oriental bitter-
sweet's ability to spread from both root sprouts and bird-dispersed seed
and its use of multiple breeding systems, some researchers have suggested
that Oriental bittersweet may become the fastest spreading invasive
species among Oriental bittersweet, Japanese stiltgrass, garlic mustard
(Alliaria officinalis), tree-of-heaven (Ailanthus altissima), and European
buckthorn (Rhamnus cathartica).
Asexual regeneration is important for Oriental bittersweet spread. Oriental
bittersweet sprouts from roots, root fragments, and the root crown. Dam-
age to the branches, root crowns, or roots encourages sprouting.
Oriental bittersweet uses both dioecious and perfect breeding systems.
This species is typically "functionally dioecious" because early abortion of
either male or female organs makes most individual plants unisexual. Plants
occasionally develop both unisexual and perfect flowers, becoming poly-
gamodioecious, and some plants are reportedly monoecious.
Bees pollinate Oriental bittersweet flowers; wind pollination also occurs.
Animals, water, and humans also disperse Oriental bittersweet seed. The
seed disperses after the 3-valved capsules split open and expose the arils.
The brightly colored, fleshy arils attract birds and small mammals, which
disperse most of the seed after ingesting the arils. The fruits can float if
they fall into water. Undispersed seed falls under or near parent plants.
Oriental bittersweet typically produces abundant flowers, fruits, and seeds.
SITE CHARACTERISTICS: In the United States, Oriental bitter-
sweet grows on woodland and forest edges; in thickets, woodlands, and
forests; and on coastal wetlands, beaches, and saltmarsh edges. Oriental
bittersweet is common on disturbed sites such as roadsides, logged forests,
and old fields. It is also common in urban areas, from which it may disperse
SEASONAL DEVELOPMENT: Oriental bittersweet starts growth in
midspring and flowers soon after. Pollen sheds about 2 weeks after flowers
open. Leaves abscise in late fall, usually later than the leaves of associated
native species. Arils and seeds mature in autumn and remain on the plant
all winter unless harvested by animals. Animals disperse the seeds through-
out autumn, winter, and into early spring, with most seeds dispersed after
leaf drop. Plants are dormant in winter.
GENERAL DISTRIBUTION: Oriental bittersweet is native to Korea,
China, and Japan. Its southern limit in southeastern Asia is along the
Yangtze River watershed . Oriental bittersweet is nonnative in North
America and New Zealand.
In North America, Oriental bittersweet is sporadically distributed from
Ontario and Quebec south through the Great Lakes states, New England,
and the Southeast to Arkansas, Tennessee, Florida, Louisiana, and the
southeastern edge of the Great Plains. It was introduced in the United
States around 1860 as an ornamental and for erosion control. It spread
to Connecticut by 1916, Massachusetts by 1919, and New Hampshire by
1938. By 1974, Oriental bittersweet had spread to 33 states and was con-
sidered invasive in 21. As of 2011, it was widespread in the Northeast
and sporadic but locally dominant farther south.
Oriental bittersweet is most common and invasive in New York, coastal
Connecticut, and the southern Appalachian Mountains. In 2008, it covered
at estimated 8,960 acres (3,630 ha) in forests of the Southeast and South.
Researchers predict that Oriental bittersweet may increase in New England
and spread further north. Based on Oriental bittersweet's native range and
habitat preferences, others also expect Oriental bittersweet to expand its
range in the United States and Canada.
SKY MEADOWS DISTRIBUTION:
Vine specimens can be found on trails marked in red.
Appalachian Trail/Old Trail
South Ridge/North Ridge
Rolling Meadows/ Lost Mountain
The specific distribution for oriental bittersweet has not been determined.
IMPORTANCE AND USES: Oriental bittersweet is a primary source
of food for both birds and small mammals (and are important for seed
dispersal). Birds are probably most important for Oriental bittersweet
seed consumption and dispersal because they are highly mobile, travel
in flocks, and often eat "voraciously". Northern flickers, yellow-rumpled
warblers, American robins and other thrushes (Turdidae), mockingbirds
and catbirds (Mimidae), and European starlings and mynas (Sturnidae)
are the primary Oriental bittersweet seed eaters while in an oak forest
in North Carolina, small animals removed 75% of the total Oriental bitter-
sweet seed crop. Near Asheville, North Carolina, birds and small mammals
dispersed Oriental bittersweet seeds in "large numbers". Consumers of
Oriental bittersweet arils include black-capped chickadees, eastern blue-
birds, northern mockingbirds, European starlings, blue jays, northern bob-
whites, ruffed grouse, ring-necked pheasants, and wild turkeys. However,
it is unclear how important Oriental bittersweet arils are as an avian food
source. Frugivorous mammals that eat the arils include fox squirrels and
eastern cottontails. White-tailed deer may browse the foliage, although the
foliage may not be preferred. In Rock Creek Park, Washington D.C.,
Oriental bittersweet was more frequent in exclosure plots than in control
plots that were accessible to white-tailed deer.
Oriental bittersweet is an Asian folk medicine used for treating rheumatoid
arthritis and bacterial infections. Medical and pharmacological studies show
that Oriental bittersweet derivatives have antitumor, antiinflammatory,
antioxidant, antibacterial, and insecticidal properties. One Oriental bitter-
sweet derivative shows ability to reverse multidrug resistance of cancer
cells to cancer-treatment drugs.
Oriental bittersweet bark is used as a fine fiber in China. Enzymes in
Oriental bittersweet leaves clot milk; leaf extracts may provide an alter-
native to calf rennet enzymes used in making cheese.
In the United States, Oriental bittersweet is commercially available and
widely planted and harvested as an ornamental. Wreaths and other orna-
ments are made from fruiting stems; Oriental bittersweet seeds may
disperse if these ornaments are discarded on favorable germination sites.
Oriental bittersweet was once widely planted in highway and "conserva-
tion" plantings, but it is not currently recommended for wildland plantings.
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