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Gooseneck loosestrife, Lysimachia clethroides, is a member of the primrose family, although this particular perennial shrub bears little resemblance to the primrose. This species is an aggressive, rapidly spreading plant that reaches 30 inches (75 cm) in height. The gooseneck loosestrife has lance-shaped leaves and tall, curved stems with masses of white flower clusters along them. Native to China and Japan, the gooseneck loosestrife is cultivated throughout the world, both as a garden plant and commercially for use as a cut flower. It is a deciduous species, meaning it sheds leaves during the winter before producing new foliage in the spring.
Considered to be both an invasive species and a noxious weed in many parts of the world, the gooseneck loosestrife spreads rapidly and forms dense, impenetrable clumps, blocking sunlight and using large amounts of nutrients. This gives more delicate natural species no chance to compete. The presence of this species can be a contributing factor to the localized endangerment of native flora in some regions.
The gooseneck loosestrife has the ability to reproduce sexually and asexually. The method of sexual reproduction for the gooseneck loosestrife is insect pollination. After the plant has flowered and died back, seeds are released and spread by wind and animal-aided dispersal.
Asexual reproduction for this species is known as rhizomatous reproduction. This means the mature plant puts out underground trailers that spread away from the parent plant. The trailers grow very rapidly and send a new shoot upward at regular intervals, producing an entirely new plant identical to the original. In the case of gooseneck loosestrife, the rhizomes produce new plants very close to the parent plant, hence the dense clumps.
Gooseneck loosestrife can be grown in large containers to reduce the species' ability to spread, but it will still produce seed heads that can be removed to eliminate spreading the plant via seeds. Plants appear to have a reduced rate of spread in drier areas. A very tolerant plant, the gooseneck loosestrife is tolerant of any soil type, providing it is moderately to very moist and has good drainage.
Although this species loves water, it does not like stagnant water or long periods of heavy waterlogging. The plants should never be allowed to dry out completely, because this will cause poor health or death. Gooseneck loosestrife prefers nutrient-heavy soil and tolerates a wide pH range and either full sun or partial shade. This species is resistant to most pests and diseases, but snails and slugs can cause extensive damage to young plants.