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Spread, Impact, and Control of Purple Loosestrife (Lythrum salicaria) in North American Wetlands

Purposeful Introduction

Most of our early records of L. salicaria's spread into the estuaries and canals of northeastern North America indicate accidental transport in ship ballast or in imported wool. Nevertheless, purposeful introduction could have occurred at a very early time and has become an increasing problem in the recent history of spread.

Purple Loosestrife as an Herb

Some of the early escapes of L. salicaria could have been from herb gardens that were established with seeds imported from northern Europe. Stevens (1961) referred to the long history of use of L. salicaria for healing. He quoted Dioscorides (1st century) as the earliest authority, who reported, "The herb is tart and strong in taste, of an astringent and refrigerant nature, good for stanching both outward and inward bleeding; sap extracted from the leaves and drunk stops blood-spitting and dysentery, and sour wine in which the leaves have been boiled when taken internally will have the same effect; and if the plant is set afire it gives off a pungent vapor and smoke that drives away serpents; and flies cannot stay in a room where this smoke is." In describing the medicinal properties of various Lythraceae, Pammel (1911) said, "Tannin occurs in the root of Lythrum salicaria." In 1916, Kraemer (as have other authors) referred to the generic name Lythrum as being derived from the Greek word for blood "perhaps because of its [loosestrife's] styptic properties." Similarly, Altschul (1973) quoted Scringe's reference to L. salicaria as "Herbe astringente, faible." More recently, Grieve (1959) noted that although L. salicaria is now seldom used, it was highly recommended in early herbals. Powders were made from dried leaves and decoctions from the roots. These were used to treat chronic diarrhea and dysentery, as well as leucorrhea and "blood-spitting." Green or dry leaves were also used to heal wounds, ulcers, and sores. Describing human use of this herb in Palestine, Zohary (1972) said, "The young leafy shoots are eaten as vegetables; the flowering branches are used in folk medicine to prepare astringents, tonics and styptics."

The careful cultivation and almost intimate settings of herb gardens would make them unlikely sites for the escape of L. salicaria. Nevertheless, as we indicated earlier, this may have been the origin of some of the early establishments along the eastern seaboard. With the rise of modern medicine, the declining interest in medicinal herbs has made the herb garden an unlikely factor in the spread of L. salicaria across North America.

Horticultural Escapes

The profuse and attractive floral displays of purple loosestrife have made the plant well known to gardeners throughout the world. Its use in Europe probably extends back into the Middle Ages; however, confusion between Lysimachia and Lythrum in early garden books makes lists of plants used somewhat uncertain (Turner 1548 as cited in Grigson 1955). Nevertheless, by the time purple loosestrife was being introduced or becoming naturalized in North America, Sweet (1839) said of Lythrum, "will thrive in garden soil … all are readily increased by dividing the root …" Similarly, the British Annals of Horticulture (Anonymous 1847) listed Lythrum salicaria as "a plant of great beauty … never to be omitted from the banks of a piece of water." Buist (1852), in an American flower garden directory, listed L. alatum, L. virgatum, L. diffusum, L. roseum, and L. lanceolatum as species that will grow well if given adequate light. Of these species, Bailey and Bailey (1976) referred to L. roseum superbum as one of many horticultural varieties of L. salicaria. In a text on garden botany, Gray (1869) noted that L. salicaria was not uncommon in old gardens. Last, referring to old gardens in Virginia, Boggs (1932) included L. salicaria as one of many plants derived from English gardens of the 17th, 18th, and early 19th centuries. Clearly, L. salicaria, or one of its horticultural varieties, was present in early American gardens and may have been a source of early escapes.

The inclusion of L. salicaria in garden and border plantings has continued throughout Canada and the United States. Several large nurseries have developed their own horticultural stocks, including strains claimed to be infertile. We have observed several relatively fragile garden Lythrums (source unknown) that did not produce seeds or capsules. Various cultivars of L. salicaria are shipped as rootstocks. In the West, at least two national retail companies currently offer L. salicaria stocks (some of them hybrids) as potted plants. Seedlings or segregates of these stocks continue to be important sources of regional and local spread in the expanding range of purple loosestrife.

Naturalization as a Honey Plant

British beekeepers were aware of the attractiveness of purple loosestrife flowers to bees (Grieve 1923); however, it was only 1 of 18 wild plants mentioned by Mace (1976) as a supplemental source of nectar and pollen in Great Britain. Although American beekeepers show more enthusiasm for purple loosestrife than do Europeans, Pellet (1947) did not include L. salicaria among wild plants of major importance as nectar and pollen sources in North America. He described purple loosestrife as "… the one plant which can be planted with confidence in boggy spots … "A query in the February 1944 issue of the American Bee Journal (Anonymous 1944) described the abundance of L. salicaria along the Merrimac River in Massachusetts and asked about its rank as a honey plant. Subsequent contributions to the American Bee Journal from Iowa (Pellet 1944), British Columbia (Van't Haaff 1968), Minnesota (Bunch 1977a), and New York (Hayes 1979) traced the growing interest in purple loosestrife as a honey plant. An apicultural supplier in the Midwest has offered purple loosestrife seed for sale, and instructions for "naturalizing" the plant have been published (Pellet 1956). The role of beekeepers in contributing to the spread of purple loosestrife is difficult to evaluate, but clearly, their efforts to "naturalize" purple loosestrife could account for many of the recent extensions of the species in the Midwest and Far West. Moreover, their efforts have not been wholly irresponsible. One honey plant enthusiast (Mead 1957) included five criteria for prospective honey plants, one being "… any danger of its becoming an offensive weed. The American Bee Journal also published a letter (Hughes 1977) and a press release (U.S. Fish and Wildlife Service [USFWS] 1979) that described the threat of purple loosestrife to wetland habitats.

Other Sources of Escapes

The last 30 years have seen the growth of a healthy and steadfast interest in the preservation of native habitats. A corresponding rise in investments in weekend cottages and the restoration of natural habitats on some of these properties has taken place. This concern has also influenced city, county, and State efforts in establishing nature preserves for the education and enjoyment of all age groups. In response to the needs of landowners or preserve managers for seed, 160 companies offer seed mixes of "wildflowers" and native prairie herbs and grasses (Wade 1985). Wade (personal communication) examined lists of species offered by more than 50 of these seed outlets and found that about 25% of the native-plant seed mixes contained alien species; 10% of the lists with alien seeds included L. salicaria. The inclusion of purple loosestrife in these seed mixes is a serious threat to regional and local habitats that have thus far escaped infestations by this alien. Indeed, prairie wetland restoration with some of these mixes would be an open invitation to habitat degradation by the dominance of purple loosestrife.

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