This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
This choice and gay-flowered plant is found to-day (not earlier) in the Temperate, Northern, and Arctic regions, Arctic Europe, and in Australia. It is found in Great Britain throughout the Peninsula, Channel, Thames, Anglia, and Severn provinces, and in S. Wales generally except in Radnor and Cardigan; in N. Wales only in Denbigh and Anglesey; and throughout the Trent, Mersey, Humber, Tyne, and Lakes provinces. In Scotland it is found throughout the West Lowlands; only in Berwick and Haddington in the E. Lowlands; in the Eastern Highlands only in Fife, Stirling, West Perth; in N. Aberdeen, Easterness, Argyle, Dumbarton, Clyde Islands, Cantire, S. Ebudes, and the Hebrides.
The Purple Loosestrife is a common riverside flower, associated with Great Yellow Cress, Great Hairy Willow Herb, Scorpion Grass, Gipsywort, Blue Skullcap, Amphibious Knotweed, Yellow Flag, Reed Mace, Sweet Flag, Flowering Rush, etc. It is hygrophilous, and grows along the margins of most watery places, preferring especially rivers, but frequenting ditches, lakes, and similar spots.
Tall and erect, this handsome riverside flower at once attracts attention. The stems are winged, or angular and branched, but never widely spreading. The leaves are lance-shaped with a heart-shaped base, and are either in whorls or opposite. They may be smooth and very narrow, as in the long-styled form, the leaves in the short-styled forms being large and more downy. The uppermost bracts are not as long as the flower. As the English name and first Greek name indicate, the flowers are purple. They are in long, tapering spikes, in whorls, with or without bracts, with a calyx with 12 ribs and awl-shaped teeth. The petals are narrow. There are 12 stamens. The three lengths of style have from Darwin's researches contributed to render the plant famous from the interest they have for us in their connection with pollination.
The plant is 2-3 ft. high. It flowers in July and August. It is a herbaceous perennial, reproduced by division, and often cultivated. The flowers are trimorphic, as noticed by Darwin or earlier by Vaucher. The stamens are in two groups, and in the one case the stigma is projecting, in the other it is shorter or included, whilst in the third case it is intermediate, and lies between the two groups of anthers, and they may thus be called long-, short-, and mid-styled forms. The ratio of size of the seeds is as 100, 142, 121. The pollen grains also differ, the largest being green, belonging to the stamens of the long-styled forms, the medium to those of the mid-styled, and those of the short-styled forms have small pollen-grains, which are yellow. The anther-stalks are pink in the longer stamens and uncoloured in the shorter.
If insects do not visit it the plant is sterile. But it is visited by numerous bees, humble bees, and flies, which settle on the stamens and pistil on the upper side. Pollen to be fertile must be transferred to a plant with flowers with the stigma at the level of the stamens from which the pollen came, and when long- and short-styled plants are crossed, the result is fertile seed. A single flower can be pollinated legitimately in two ways, and illegitimately in four ways; and there are 18 modes of union, 6 legitimate, 12 illegitimate, in the union of three forms. Trimorphism may be advantageous. The chances are 2 to 1 in favour of forms being different and incapable of self-pollination.
Photo. B. Hanley - Purple Loosestrife (Lythrum Salicaria, L.)
The capsule, which is egg-shaped and 1-2-celled, is divided by septa and opens along the centre of each valve irregularly, allowing the numerous small yellow seeds to be thrown out to some distance. When blown or cast up on the water they are able to float.
Purple Loosestrife is a peat- or humus-loving plant, growing in wet peaty ground close to water, and is often submerged.
The beetles, Galeruca calmariensis; Haltica lythri, Aphthona lute-scens, Ochrosis salicariae, and Psylliodes picina, Apion vernale, feed on it, and the Lepidoptera, Small Elephant Hawk Moth (Chaerocampa elpenor), and the V Pug (Etipithecia coronata).
Lythrum, Linnaeus, is from the Greek lythron, gore, from the purple colour of the flowers, and Salicaria, Tournefort, is from salix, willow, from the shape of the leaves.
Purple Loosestrife is called Purple Grass, Herb Willow, Long Purples, Purple Loose-strife, Red Sally, Soldiers, Spiked Willow Herb.
This plant is called Red Sally in Lancashire, where it is much gathered for medicinal use. In Clare's "Village Minstrel" it is called Long Purples: "Gay long-purples with its tufty spike She'd wade o'er shoes to reach it in the dyke".
The plant is astringent and tonic, and is much used in Ireland on account of those properties. It has also been used in tanning.
Essential Specific Characters:117. Lythrum Salicaria, L. - Stem tall, erect, leaves lanceolate, cordate below, opposite, flowers purple, in whorls in spikes, stamens 12, long and short, calyx teeth alternately long and spreading.