Purple loosestrife
Lythraceae - Lythrum salicaria
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What does it look like?

Purple loosestrife is an erect, summer-green perennial herb that grows 1-2m tall.  The woody stems are square in cross-section.  It has narrow leaves, which are usually paired and are heart-shaped at the base.  From December to February it produces 20-25cm long spikes of purple-magenta flowers.  The flowers are followed by blackish seed capsules that are 3-5mm long.

 

Why is it a problem?

Purple loosestrife is a highly aggressive invader of damp ground, wetlands and shallow water.  It over-tops native species with its dense, bushy growth and is long-lived.  It tolerates hot or cold conditions and low to high nutrient levels, though it is intolerant of salt water.

Purple loosestrife reproduces mostly by seed but re-growth from plant fragments has also been observed.  It produces millions of long-lived, highly viable seeds that can remain viable in the soil for many years.  Seeds submerged in water can remain viable for 1-2 years. For germination, disturbed sites or open, moist substrates are preferred.

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