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'Purple loosestrife' ('''Lythrum salicaria''') is a semi-aquatic herbaceous plant belonging to the loosestrife family, Lythraceae, native to the wetlands of Eurasia. Other names include 'spiked loosestrife', 'purple lythrum', or 'salicaire'. It should not be confused with other plants sharing the name ''loosestrife'' that are members of the family Primulaceae.

Contents

Description

Cultivation and uses

Biological control

External links

Further reading

Description

It is a herbaceous perennial plant, growing 1-2 m tall, forming clonal colonies 1.5 m or more in width with numerous erect stems growing from a single woody root mass. The stems are reddish-purple or red to purple and square in cross-section. The leaves are lanceolate, 3-10 cm long and 1-2 cm broad, downy and sessile, and arranged opposite or in whorls of three. The flowers are reddish purple, 10-15 mm diameter, with six petals (occasionally five), and are clustered tightly in the axils of bracts or leaves. The fruit is a small 3-4 mm capsule containing numerous minute seeds. Flowering lasts throughout the summer. When the seeds are mature, the leaves often turn bright red through dehydration in early autumn; the red colour may last for almost two weeks. The dead stalks from previous growing seasons are brown.
In North America, purple loosestrife may be distinguished from similar native plants (e.g. fireweed ''Epilobium angustifolium'', blue vervain ''Verbena hastata'', Liatris ''Liatris'' spp., and spiraea ''Spiraea douglasii'') by its angular stalks which are square in outline, as well by it leaves, which are in pairs that alternate at right angle and are not serrated.

Cultivation and uses

Purple loosestrife has become a widespread species since its introduction into temperate New Zealand and North America where it is officially listed in some states as a noxious weed or invasive species. The seeds probably first arrived in the plant's non-native areas in muddy ballast water emptied from ships. It has also been used as a medicinal herb and cultivated as a garden plant. The flowers are quite showy and bright.
The plants grow vigorously and spread very fast when removed from their natural controlling agents. Infestations result in dramatic disruption in water flow in rivers and canals, and a sharp decline in biological diversity as native food and cover plant species, notably cattails, are completely crowded out, and the life cycles of organisms from waterfowl to amphibians to algae are affected. There is, however, a confounding view to the these claims, namely that they are not supported by conclusive scientific evidence, but rather an overwhelming number of subjective observations (Hager and McCoy 1998). A study of 41 plots in Ontario found that a number of native species were more likely to grow in plots containing purple loosestrife, and that there was no significant difference in vascular plant species richness regardless of purple loosestrife concentration (Treberd & Husband 1999). Many studies contain records of native species out-competing loosestrife, and many species using it for food, shelter, or nesting sites (Anderson 1995. Barbour & Kiviat 1997, Kiviat 1978). A study of 258 plots in Lake Huron wetlands concluded that "avian use may be higher than is commonly believed" (Whitt et al.)

Purple loosestrife is sold in some areas as an ornamental. Plants marketed under the name European wand loosestrife (''L. virgatum'') are in fact the same species as purple loosestrife despite the different name. In some cases the plants sold are assumed to be sterile; in fact, this is rarely the case. The sale of purple loosestrife is illegal in some areas.

Biological control

A single plant may produce up to three million tiny seeds annually. Easily carried by wind and water, the seeds germinate in moist soils after overwintering. The plant can also sprout anew from pieces of root left in the soil or water. Once established, loosestrife stands are difficult and costly to remove by mechanical and chemical means.
Purple loosestrife provides a model of successful biological pest control. Research began in 1985 and today the plant is managed well with a number of insects that feed on it. Four species of beetle use purple loosestrife as their natural food source and they can do significant damage to the plant. The beetles used as biological control agents include two species of leaf beetle and two species of weevil.

★ The black-margined loosestrife beetle ''Galerucella calmariensis'' is a brown beetle with a black line on its thorax. The adult feeds on the leaves of the plant, producing characteristic round holes. Its larvae destroy tender leaf buds and strip the tissue from the leaves.

★ The golden loosestrife beetle ''Galerucella pusilla'' is nearly identical to ''G. calmariensis'', but usually lacks the black thoracic line. Its feeding habits are also quite similar to the other leaf beetle. An infestation of either of these insects is extremely effective in wiping out a stand of purple loosestrife, defoliating up to 100% of the plants in an area.

★ The loosestrife root weevil ''Hylobius transversovittatus'' is a large red nocturnal weevil, which spends its nights feeding on leaves and leaf buds. The larvae emerge from their eggs and immediately burrow into the root of the plant, which they feed on continuously for over a year. This root damage stunts the plant's growth and ability to create seeds. If several larvae inhabit the same root, the plant can be killed.

★ The loosestrife flower weevil ''Nanophyes marmoratus'' is a tiny weevil which lays a single egg in each flower. When the larvae emerge they eat the flowers' ovaries, and the plant is unable to create seed. The larvae usually proceed to hollow out the flower buds and use them as safe places to pupate.
Caterpillars of The Engrailed (''Ectropis crepuscularia''), a geometer moth, also feed on Purple Loosestrife. This moth, however, is a pest species itself and unsuitable for biological control.

External links

★ National Park Service - Purple Loosestrife Facts

Further reading

★ Biology and Biological Control of Purple Loosestrife, L. M. Wilson, M. Schwarzlaender, B. Blossey & C. B. Randall, , , Morgantown, WV: Forest Health Technology Enterprise Team, United States Department of Agriculture, 2004,

★ The implacations of accepting untested hypothesis:a review of the effects of purple loosestrife (''Lythrum salicaria'') in North America, H. Hager& K. McCoy, , , Biodiversity and Conservation, 1998

★ Invasion Biology: Critique of a Pseudoscience., Theodoropoulos, David., , , Avvar Books, Blythe, CA., 2003., ISBN 0-9708504-1-7

★ Anderson, M. G., 1995. Interactions between Lythrum salicaria and native organisms: A critical review. Environmental Management 19:225-231.

★ Barbour, J. G. and E. Kiviat. 1997. Introduced purple loosestrife as host of native Saturniidae (Lepidoptera). The Great Lakes Entomologist. 30:115-122

★ Kiviat, E. 1978. American goldfinch nests in purple loosestrife. Wilson Bulletin 108:182-186.

★ Treberg, M. A., and B. C. Husband. 1999. Relationship between the abundance of Lythrum salicaria (purple loosestrife) and plant species richness along the Bar River, Canada. Wetlands 19:118-125.

★ Whitt, M. B., H. H. Prince, and R. R. Cox, Jr. 1999. Avian use of purple loosestrife dominated habitat relative to other vegetation types in the Lake Huron wetland complex. The Wilson Bulletin 111:105-114.