IS AMERICA'S MOST POPULAR PARASITE
December 19, 2010
One of my
daughters suggested I choose a topic for this week associated with the
holiday season. I've written about holly and reindeer in recent years,
so let's return to mistletoe, a plant that has flowers pollinated by insects,
has seeds transported by birds, and takes its water and minerals from
refers to any of more than 200 species of semiparasitic shrubs found worldwide.
Mistletoe lives throughout the southern United States, from the Atlantic
Coast to California, and on every continent except Antarctica. Like true
parasitic plants, mistletoe is devoid of roots. Instead, the dark green
shrub has extensions called holdfasts that grip the host tree. These rootlike
anchors suck water and nutrients from the tree. Thus, mistletoe is only
found on living trees, which are essential to the mistletoe's survival.
In contrast, Spanish moss uses a tree, dead or alive, only for support,
extracting water and nutrients from the atmosphere.
In the South,
tiny yellow flowers bloom on the evergreen mistletoe from fall to winter.
The familiar white berries, which begin to form soon after pollination,
resemble little packets of glue around tiny indigestible seeds. A mistletoe
plant can be either male or female and, like a holly tree, only the female
plant has berries. Eating mistletoe berries may be potentially lethal
for humans, but birds seem to be immune to any toxicity.
to mistletoe's poisonous qualities is essential to the welfare of the
plant. The dispersal and propagation of mistletoe is largely dependent
on birds that eat the berries but do not digest the seeds. Ecological
studies suggest that seeds are most likely to survive and grow if a bird
deposits them on the same species of tree on which the parent plant lived.
During spring migration, a flock of cedar waxwings can result in newly
developing mistletoe plants being far away from where the seeds were ingested.
Mistletoe thrives in bright sunlight in the uppermost branches of big
oaks and is typically absent from pines and from evergreen hardwoods such
as magnolias with needles and leaves that would shade the mistletoe.
lifestyle is unusual among flowering plants. Nonetheless, many aspects
of mistletoe ecology are well understood. Competition to obtain water,
minerals and even space itself, is highly intense among most plants, but
mistletoe does not encounter such problems. Tree limbs are a ready source
of water and minerals for this unusual little plant, and its absence from
the uppermost branches of a tall oak is probably because no bird has dropped
a seed there, not because of competition with other mistletoe plants.
ages, mistletoe has been credited with some intriguing qualities, perhaps,
in part, because of its many unusual ecological properties. According
to Scandinavian legend, mistletoe was the only organism in the world from
which Odin's son Baldur was not protected, and a mistletoe dart was the
cause of his death.
is also associated with the Druids, the mysterious, oak-worshiping sect
that inhabited the British Isles centuries ago. The Druids considered
mistletoe a plant of honor and power. According to legend, when the plant
was found growing in an oak tree, the Druids performed sacrificial ceremonies
at the tree on the sixth day after a full moon. The Druids reportedly
used a golden sickle when harvesting mistletoe from a sacred oak. Although
the berries appear just in time for Christmas, mistletoe is not used in
churches. One reason may be because of its association with the Druids.
as a romantic lure was common in England at least as early as the 1500s.
In 1520, William Irving wrote that a young man should pluck a berry each
time he kissed a girl beneath the mistletoe. A version of that tradition
persists today in secular Christmas decorations. And though mistletoe
may be excluded from wreaths and floral displays in churches, it will
be found in many a home during this season, hanging in a doorway and enticing
people to exchange a holiday kiss.
you have an environmental question or comment, email