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Lythrum salicaria (Purple-loosestrife[1]) is a flowering plant belonging to the family Lythraceae, native to Europe, Asia, northwest Africa, and southeastern Australia.[2][3][4][5] The name is commonly cited unhyphenated as purple loosestrife, but it should not be confused with other plants sharing the name loosestrife that are members of the family Primulaceae. Other names include spiked loosestrife, or purple lythrum; in French it is salicaire, and in Chinese 千屈菜 qian qu cai.
Description
It is a herbaceous perennial plant, growing 1-1.5 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 5-15 mm broad, downy and sessile, and arranged opposite or in whorls of three. The flowers are reddish purple, 10-20 mm diameter, with six petals (occasionally five) and 12 stamens, and are clustered tightly in the axils of bracts or leaves; there are three different flower types, with the stamens and style of different lengths, short, medium or long; each flower type can only be pollinated by one of the other types, not the same type, thus ensuring cross-pollination between different plants. 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.[1][4][6]
The species is very variable in leaf shape and degree of hariness, and a number of subspecies and varieties have been described, but it is now generally regarded as monotypic with none of these variants being considered of botanical significance. The species Lythrum intermedium Ledeb. ex Colla is also now considered synonymous.[2][4]
Ecology
Lythrum salicaria is a wetland plant, growing in shallow freshwater pond edges, marshes, and fens, on fertile, neutral to slightly alkaline soils.[1][6]
Associated insects
The flowers are pollinated by long-tongued insects, including bees and butterflies.[6]
A number of insects use Lythrum salicaria as a food resouce.
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.
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 moth (Ectropis crepuscularia), a polyphagous geometer moth, also feed on Purple Loosestrife.
Cultivation and uses
It has been used as an astringent medicinal herb to treat diarrhoea and dysentery; it is considered safe to use for all ages, including babies.[7] It is also cultivated as an ornamental plant in gardens. The flowers are showy and bright, and a number of cultivars have been selected for variation in flower colour, including 'Atropurpureum' with dark purple flowers, 'Brightness' with deep pink flowers, 'Happy' with red flowers on a short (60 cm) stem, 'Purple Spires' with purple flowers on a tall stem, and 'Roseum Superbum' with large pink flowers.[8]
As an invasive species
The purple loosestrife has been introduced into temperate New Zealand and North America where it is now widely naturalised and officially listed in some areas as a noxious weed or invasive species.[9] The seeds probably first arrived in the plant's non-native areas in muddy ballast water emptied from ships. 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 contrary view to the these claims, that they are not supported by conclusive scientific evidence, but are rather an overwhelming number of subjective observations.[10][11] 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.[12] Many studies contain records of native species out-competing loosestrife, and many species using it for food, shelter, or nesting sites.[13][14][15] A study of 258 plots in Lake Huron wetlands concluded that "avian use may be higher than is commonly believed".[16]
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.
Plants marketed under the name "European wand loosestrife" (L. virgatum) are in fact the same species despite the different name. In some cases the plants sold are claimed to be sterile; this is rarely the case. Its sale is illegal in some areas.
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.
Biological control
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, Galerucella calmariensis and G. pusilla, and two species of weevil, Hylobius transversovittatus and Nanophyes marmoratus. Infestations of either of the Galerucella species is extremely effective in wiping out a stand of purple loosestrife, defoliating up to 100% of the plants in an area. The moth Ectropis crepuscularia is a pest species itself and unsuitable for biological control.[17]
References
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- ↑ 1.0 1.1 1.2 Flora of NW Europe: Lythrum salicaria
- ↑ 2.0 2.1 Flora Europaea: Lythrum salicaria
- ↑ Med-Checklist: [ Lythrum salicaria]
- ↑ 4.0 4.1 4.2 Flora of China: Lythrum salicaria
- ↑ Australian Plant Names Index: Lythrum salicaria
- ↑ 6.0 6.1 6.2 Blamey, M. & Grey-Wilson, C. (1989). Flora of Britain and Northern Europe. ISBN 0-340-40170-2
- ↑ Plants for a Future: Lythrum salicaria
- ↑ Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
- ↑ US National Park Service: Purple Loosestrife
- ↑ Hager, H. & McCoy, K. (1998). The implacations of accepting untested hypothesis: a review of the effects of purple loosestrife (Lythrum salicaria) in North America. Biodiversity and Conservation 7: 1069–1079.
- ↑ Theodoropoulos, D. (2003). Invasion Biology: Critique of a Pseudoscience pp.37-38, 94, 115, 134. Avvar Books, Blythe, CA. ISBN 0-9708504-1-7.
- ↑ 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.
- ↑ Anderson, M. G. (1995). Interactions between Lythrum salicaria and native organisms: A critical review. Environmental Management 19: 225-231.
- ↑ Barbour, J. G. & Kiviat, E. (1997). Introduced purple loosestrife as host of native Saturniidae (Lepidoptera). Great Lakes Entomologist 30: 115-122.
- ↑ Kiviat, E. 1978. American goldfinch nests in purple loosestrife. Wilson Bulletin 108: 182-186.
- ↑ Whitt, M. B., Prince, H. H. & Cox, R. R., Jr. (1999). Avian use of purple loosestrife dominated habitat relative to other vegetation types in the Lake Huron wetland complex. Wilson Bulletin 111: 105-114.
- ↑ Wilson, L. M., Schwarzlaender, M., Blossey, B., & Randall, C. B. (2004). Biology and Biological Control of Purple Loosestrife. Morgantown, WV: USDA Forest Health Technology Enterprise Team.