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| When I was a child in upstate New York, we treasured the
American Bittersweet, Celastrus scandens, a rare and
beautiful plant on the local endangered list. Today, on the
Connecticut shoreline, I pull up a lot of its Asian cousin,
the Oriental or Asiatic Bittersweet, Celastrus orbiculatus. |
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picture: Asiatic Bittersweet
(Celastrus orbiculatus) through out the year
in downtown Stamford, CT |
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The native plant grows 10’ to 20’ vines and
spreads slowly. Its natural range is Ontario to
Manitoba, south to North Carolina and New Mexico
(Zones 3- 8). It has separate male and female plants
and is bee-pollinated. Its berries are munched up by
chickadees, blue jays and mockingbirds, to name a
few. It is late-winter survival food for many
species, including squirrels. (“Late-winter survival
food” means that they don’t like it a whole lot but
will eat it when they have to.) The berries aren’t
fatal to humans but shouldn’t be eaten because they
are guaranteed to clean out the alimentary system in
short, albeit painful, order. The beautiful but
deadly invasive cousin, a native of Eastern
Asia, Korea, China, and Japan, was first imported to
North America in the 1860’s.
Ironically, it was a favorite of
conservationists as a quick growing
groundcover that provided shelter and food
for wildlife, protected against soil and
dune erosion, had a 95% seed germination
rate, made great material for floral
arrangements, and had attractive
golden-yellow fall foliage.
How could you lose? Well, if you wanted an
awful lot of the stuff, growing 60’ vines,
to the exclusion of a more diverse
community, you couldn’t. It’s now in 33
states from Connecticut to North Carolina
and west to Illinois. Because its as salt
tolerant as its American cousin, it’s
particularly a problem around the Long
Island Sound. It’s now reaching up in
Ontario. However, those of you out West can
still beat it back. |
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Picture: Asiatic
Bittersweet (Celastrus orbiculatus) in flower Spring
2004 Hoyt Street Ally, Stamford CT |
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You often spot the invader in the form of
seedlings under any tree where birds roost.
In the mulch under a street elm in Downtown
Stamford the other day, the weed population
was 15 bittersweet seedlings, one woodbine,
and 2 crab grass. This should give you an
idea of the plant’s ability to spread.
The adult Asiatic Bittersweet’s leaves
are rounded with pointed tips and
finely-toothed margins. The leaves can be
almost lime-green in spring, maturing the
mid-green and then yellowing as the berries
ripen in August. Finally, just past the high
of the fall color, the leaves will be a
spectacular golden-yellow for a week or two.
Asiatic Bittersweet has small green-white
flowers in late spring. The female plants
then follow through with clusters of round
green berries that grow to pea size. The
berries turn yellow, then orange. In the
early fall, they split to reveal the bright
red inner fruit. The fruit persists until
munched up by the fauna in January or
February (or until you throw out the wreath
that the florist made from it).
Asiatic Bittersweet makes a twining,
woody vine that kills supporting plants by
strangling and shading. Many host plants
also succumb to wind and ice with the added
weight of the vine. The invader uses root
suckering to spread until it’s a dense
thicket. The vine can swell over time into a
4” diameter trunk with exfoliating bark.
Asiatic Bittersweet spreads rapidly
between locations by prolific, bird-carried
seeds. Every winter, at the local
supermarket, the sidewalk beneath the
English sparrows roost is red with Asiatic
Bittersweet rinds which have passed through
the birds’ stomachs. |
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Picture: Asiatic
Bittersweet (Celastrus orbiculatus) flower buds
Spring 2004 Hoyt Street Ally, Stamford CT |
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The drive to control the Asiatic bittersweet
has further endangered the American native
because the two plants look so similar. To
make matters worse, there are reports of
interbreeding. Differences between
the native and its invading cousin.
• The Asiatic flowers and fruits at the
branch tips and in the joints between the
leaves and the stem; the American flowers
and fruits only at the branch tips.
• The Asiatic can grow to 60; the American
usually only makes 10’ to 20’.
• The Asiatic has yellow to yellow-orange
seed covers; the American has orange seed
covers.
• The Asiatic has bright red seeds; the
American’s seed are less bright, sometimes
more orange.
• The Asiatic grows very quickly: the
American’s a slow grower.
If a small bittersweet seedling or vine
appears in your garden, along your roadside
or in your woodlot, you can be pretty sure
it’s Asiatic. I don’t recommend waiting
until it grows up and fruits (and becomes
impossible to root out) to make sure it’s
not one of the good guys.
Controlling the Asiatic
Bittersweet:
• you can manually remove by pulling up
all (yes, every little bit) of the root;
this works well with seedlings and small
plants.
• larger plants can be repeatedly cut to the
ground (at least 3 times a season)
• After cutting to the ground, particularly
in late summer- early fall, when the plant
is sending its stores down into the roots
for winter, the stumps can be (carefully)
painted with an appropriate herbicide.
Always use
'cides sparingly, as a last resort, with
great caution, and according to the label.
• Seed bank lasts several years and birds
will frequently re-seed near roosting areas,
so continue monitor the area at least twice
a season for seedlings.
Lastly, kill the berries from wreaths and
uproots plants by baking them in the sun for
weeks in a sealed black plastic bag. If you
dump the uprooted plant or a wreath in the
garbage, guess what you get at the dump?
More bittersweet! Indeed, discarded floral
wreaths have been a major cause of seed
dispersal. |
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Pictures: samples of
Asiatic Bittersweet (Celastrus orbiculatus) leaves |
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picture: Asiatic
Bittersweet (Celastrus orbiculatus) vine strangling a
choke cherry tree, Hoyt Street, Stamford CT 2004 |
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picture: detail of the
above Asiatic Bittersweet (Celastrus orbiculatus)
vine’s trunk. |
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Further Reading:
Invasive Plants: Weeds of the Global Garden
(Brooklyn Botanic Garden)
Invasive Plants: Changing the Landscape of
America
Plant Invaders
Easy Care Native Plants: A Guide to
Selecting and Using Beautiful American
Flowers, Shrubs, and Trees in Gardens and
Landscapes
Native Trees, Shrubs, and Vines: A Guide to
Using, Growing, and Propagating North
American Woody Plants |
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