Loosestrife, Purple, Lythrum salicaria

Life Cycle

Reproducing only by seed.


Stems tall, erect, 60-120cm high, somewhat branched, usually finely hairy, more or less square in cross-section, especially where the leaves are opposite.


Leaves opposite (2 per node) or sometimes whorled (3 or more per node), stalkless, broad near the base and tapering towards the tip, 3-10cm long, finely hairy; upper leaves and those in the inflorescence usually alternate (1 per node) and smaller than the lower ones.

Flowers and Fruit

Flowers in dense terminal spikes; sepals united into a column with 8 to 10 or 12 prominent green veins and ending in several, long, thin, pointed lobes; petals 5 to 7, red-purple, 7-10mm long, very showy; stamens several and 1 pistil; seedpod small, containing many tiny seeds. Flowers from June to autumn.


Purple loosestrife was introduced from Europe but is now widely naturalized in wet meadows, river flood-plains, and damp roadsides throughout most of Ontario.

Distinguishing Features

Its opposite leaves and square stems resemble plants of the Mint Family but it is distinguished by having separate petals, a seedpod with many fine seeds, and it lacks the minty odour.

Figure #1.

Purple loosestrife

Figure #2.

Purple loosestrife on roadside growing in Central Ontario, August.

Figure #3.

Dense terminal spikes

Figure #4.

Flowers of purple loosetrife

Figure #5.

Figure #6.

Opposite leaf arrangement.

Figure #7.

Leaf of purple loosestrife

Figure #8.

Figure #9.

Back of leaf.