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Purple Loosestrife

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1461 words
Science & Nature

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The scene is breathtakingly beautiful, a thick brush of purple flowers blankets
Canada's wetlands. This blanket silences the expected sounds of the wetland
environment, birds chirping, ducks splashing, insects buzzing and animals
thriving. This unnatural silence is disturbing, the favourite flowers that used
to litter this landscape are no longer visible, the water that used to ripple
continuously is perfectly still. The wetland is dead, except for this
overpowering, hardy purple flower that has choked out all other vegetation and
species. Purple loosestrife now controls this landscape.

Purple loosestrife is an exotic species that was introduced to North America
from Europe during the early 1800's. Europeans sailing to North America would
fill their ships ballast with wet sand taken from shores of Europe, a habitat
where purple loosestrife thrived. Upon arrival in North America the ballast
would be dumped overboard on the shoreline. By 1830 the plant was well
established along the New England seaboard. Purple loosestrife seeds were also
found in sheep and livestock feed that was imported from Europe during this
period. This new organism was introduced to a new habitat free from traditional
parasites, predators and competitors, purple loosestrife thrived in the
environmental conditions and by 1880 was rapidly spreading north and west
through the canal and marine routes. Purple loosestrife stands also increased
due to the importation of seeds and root stalks by horticulturists. It was
introduced to many communities as an herb, an ornamental garden flower and as a
desirable honey plant.

One of the earliest reported studies of purple loosestrife being a problem in
Canada was documented by Mr. Louis - Marie, in 1944. He stated that purple
loosestrife was invading the St. Lawrence flood plain pastures between Montreal
and Quebec. At that time Louis - Marie conducted a study to find suitable
control methods for purple loosestrife. His results indicated that repeated
mowing, continuous grazing, deep discing and harrowing were effective in keeping
the spread of purple loosestrife controlled on agriculture land. Since the
1940's purple loosestrife infestations have increased greatly and the plant is
now a major problem threatening many wetland ecosystems across North America.

Figure 1 - Purple loosestrife flowers.
(Parker 1993)

Lythrum Salicaria, commonly known as purple loosestrife belongs to the
Lythraceae family, which consists of 25 genera and 550 species worldwide. The
genus Lythrum consists of thirty - five species, two of which are located in
North America, Lythrum Purish which is native to the continent and the invasive
purple loosestrife. Through cross breeding, purple loosestrife is quickly
overtaking Lythrum Purish and causing a decrease in native species. "The
generic name comes from the Greek luthrum, blood, possibly in reference to the
colour of the flowers or to one of it's herbal uses, as an astringent to stop
the flow of blood." (Canadian Wildlife Federation 1993, 38) Purple loosestrife,
an aggressive, competitive, invasive weed often grows to the height of a human
and when it is mature can be 1.5 metres in width. The stalk of the plant is
square and woody and may grow to 50 centimeters in diameter. The perennial
rootstock can give rise to 50 stems annually which produce smooth edged leaves
on oppositesides of the stalk. Purple loosestrife flowers are long pink and
purple spikes which bloom from June to September (Figure 1). One purple
loosestrife plant alone is solid and hardy but when this plant invades an area
it creates a "dense, impermeable stands which

Figure 2 - Purple loosestrife growing in a typical habitat.
(Parker 1993)

are unsuitable as cover, food or resting sites for a wide range of native
wetland animals..." (Michigan Department of Natural Resources 1994). Due to the
lack of predators which feed upon purple loosestrife, this dominant plant has an
advantage when competing against most other native wetland species for food
sunlight and space. These advantages allow purple loosestrife to create dense,
monotypic stands which reduce the size and diversity of native plant populations.
Purple loosestrife can also grow on a range of substrates and under nutrient
deficit conditions. It has the ability to regenerate quickly after cutting or
damage and can withstand flooding once adult plants have been established. There
are no native species that are as hardy as purple loosestrife, therefore without
competition and predators the wetland ecosystem cannot control the spread of
purple loosestrife.

Purple loosestrife is now found world wide in wet, marshy places, coastal areas,
ditches and stream banks. (See Figure 2) It is prevalent in most of Europe and
Asia, the former USSR, the Middle East, North Africa, Tasmania, Australia and
North America. It has not been found in cold Arctic regions. In North America
purple loosestrife is located between the Canadian territories and north of the
35th parallel with the exception of Montana. The most serious infestations are
found in the wetlands of Southern Quebec and Ontario and along the Red and
Assiniboine Rivers in Manitoba. Second to Manitoba, British Columbia has the
next largest purple loosestrife infestation, weed populations are reported from
Vancouver Island to the lower Fraser and Okanogan Rivers south of Penticton. In
Saskatchewan and Alberta. small, isolated stands of purple loosestrife are
reported and the Atlantic Provinces are quickly being invaded. Currently areas
that are sensitive to the new invasions are the salt and freshwater marshes in
the Maritimes. (See Figure 3)

Figure 4 - Purple loosestrife seedling.
(Parker 1993)

Regardless of the purple loosestrife location, one of the main reasons for the
rapid infestations is due to the plants prolific seed production and
reproduction cycle. "It has been estimated that a mature plant can produce 2.7
million seeds per growing season" (DeClerck-Float 1992,15). Purple loosestrife
seeds are small and easily transported by water or by mud that attaches to the
feet of birds or off road vehicles. The seeds remain dormant over the winter and
germinate in late spring or early summer. They are capable of germinating in
either the mud or when submerged under water providing the water temperature is
between 15 - 20 oC and there are adequate light levels (See Figure 4). Through
experiments performed by S.R.A. Shamsi and F.H. Whitehead, it has been
determined that "prolonged seed dormancy may be possible, since seeds stored for
three years in a refrigerator at 3 - 4 oC were still useable and had a
germination rate of 80% " (DeClerck-Float 1992,15). The production of purple
loosestrife seeds and their exclusive characteristics allow the plants to
develop large seed banks at a site which is a factor that makes purple
loosestrife so difficult to control. The plant has the ability to reproduce from
the seed bank. Purple loosestrife can also spread vegetatively by adventitious
shoots and roots from clipped or tramped plants. Any part of the plant that
falls to the ground, even from a wheelbarrow, can develop into a plant. This
shows the plant's desire to live no matter what obstacles it faces, again making
it very difficult to control. Purple loosestrife plants have three style lengths
(short, mid, long) and three strengths (short, mid, long). Pollination occurs
between plants with the same style and stamen length. Purple loosestrife flowers
have of one style length and the two sets of stamens are different lengths,
therefore a plant is technically self - incompatible. "However, Ottenbriet
(1991), found that the self - incompatibility system is not strict, as mid -
styled plants showed a highdegree of self fertility with themselves and other
mid - styled plants." (DeClerck - Float 1992, 16) This proves, it is not safe to
plant self - incompatible purple loosestrife, there is a risk of pollination
which will lead to further distribution of the plant. This misconception is a
problem because nurseries are selling self - incompatible plants as garden
flowers which reproduce with themselves or with other species from the
loosestrife family creating more invasive stands.

Purple loosestrife's hardy, competitive and reproductive characteristics
classifies it as a large environmental concern. The plant is threatening wet
lands, decreasing water foul population, clogging irrigation systems and
becoming a threat to the fisheries. "Mosquin and Whiting (1992) regard purple
loosestrife to be one of the five invasive alien plants that have had a major
impact on natural ecosystems in Canada." (...

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Keywords: purple loosestrife scientific name, purple loosestrife invasive, purple loosestrife origin, purple loosestrife ontario, purple loosestrife drawing, purple loosestrife uk, purple loosestrife seeds, purple loosestrife food web

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