Species

Lythrum salicaria

Common Name(s)

purple loosestrife

Family

Lythraceae

Brief Description

Tall emergent perennial herb. Normally 60-100 cm tall, but can grow taller. Purple flowers in dense terminal spikes. Stems are angled (4-6 sided). The stalkless leaves can be opposite, often with alternating pairs at 90 degree angles, or sometimes in whorls of 3 near the base. The upper leaves and floral bracts can be alternate. The leaves are 5-12 cm long, wider and rounded or heart-shaped at the base. Leaf shape varies from lanceolate to narrowly oblong. Leaf sometimes covered with fine hairs.

Flora Category

Vascular - Exotic

Structural Class

Dicotyledonous Herbs other than Composites

Distribution

Locally naturalised, especially in Horowhenua and Canterbury.

Habitat

Lake margins and other wetlands.

Features

Hairy perennial herb growing from extensive rootstock. Stems 1-2 m tall, square in cross section. Leaves opposite and decussate, lance shaped, without petioles, 20-95 mm long and 5-27 mm wide. Leaf bases tend to be rounded or heart-shaped. Flowers in a branched terminal inflorescence, deep pink, showy; occurring Dec-Feb. Seed capsule blackish, 3-5 mm long. Plants are not self-fertile, so seed is only formed where more than one genotype is present.

Similar Taxa

Lythrum virgatum is occasionally cultivated and has a similar growth habit, but smaller in all parts. It is also glabrous and has narrower leaves.

Flowering

December, January, February

Flower Colours

Red / Pink

Fruiting

Autumn

Year Naturalised

1958

Origin

Native to Europe, Asia and Australia.

Reason for Introduction

Ornamental pond and garden plant

Control Techniques

Notify regional council if found

Life Cycle and Dispersal

Seed or vegetative fragments. Water dispersed, also deliberate planting. Seeds viable for up to 3 years; 2.5 million seeds can be produced per plant.

Tolerances

A wide tolerance of varying physical and chemical conditions (characteristic of disturbed habitats) e.g. tolerates P and N deficiencies by increasing root to shoot ratio; copes with rising water levels by growth in submerged stems; tolerates trampling, cutting, crushing of stems by growing shoot and root buds at the site of damage; adjusts to decrease in light level with changes in leaf morphology. Seeds can germinate in a pH range 4.0-9.1.

Attribution

Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA). Tolerance description from Thompson et al., 1987.

This page last updated on 21 Aug 2013