Purple Loosestrife (Lythrum salicaria)
WEED ALERT
Purple
loosestrife is an aggressive, herbaceous semi-aquatic perennial plant native to
Europe. Originally introduced to North America in the 1800's as an ornamental,
purple loosestrife has now naturalized and spread across Canada and the northern
US. This invasive plant is found in shallow wetlands where it aggressively
degrades and crowds out the natural vegetation required by wildlife. It is
common in southwest BC, particularly on Vancouver Island and the lower Fraser
Valley and is found frequently in the Okanagan. Smaller infestations are known
from the Kootenays and most recently, from the Quesnel area.
Biology
Purple loosestrife is a hardy, upright perennial that grows to 2 metres.
Stems are 4-sided (square), and woody with several stalks per plant. Leaves are
long and linear with smooth edges that attach directly to the stem on opposite
sides. The numerous flowers with 5-6 petals, are pink-purple in colour and
develop from June to September on the terminal spike of each stem.
Reproduction
Reproduction is both by seed and root fragments. Each plant is capable of
production up to 2.5 million seeds. Seeds are small and are readily dispersed by
moving water, wind, waterfowl, other wildlife and humans. Seeds remain dormant
over winter and germinate the following spring or early summer. Seeds may lay
dormant for many years before sprouting. Purple loosestrife can also reproduce
from root fragments or pieces that may sprout new plants.
Habitat
Purple loosestrife invades wetlands. Lake and river shores, ditchbanks,
marshlands, freshwater tidal flats, and riparian meadows are the predominent
areas where puple loosestrife will invade and establish. In some locations
purple loosestrife has also begun invading drier sites such as pastures and
cropland.
Concern
Purple loosestrife invades wetland areas where it is able to outcompete most
native wetland plant species. As a purple loosestrife infestation increases, the
size and diversity of the native plant population decreases, often threatening
scarce or rare plants. As purple loosestrife dominates an area, the natural
foods and protective cover required for wildlife survival is lost. This may
result in the loss of wildlife species or displacement from their natural
habitat.
Purple loosestrife - square stem
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Purple loosestrife - seedheads |
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