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 is a marsh plant, not yet found in Glacial plant beds in the Northern Temperate and Arctic Zones in Arctic Europe, North Africa, N. Asia, and it is represented in Australia by a nearly allied species. In Great Britain it is not found in the Peninsula province in N. Devon, but is general in the Channel, Thames, and Anglia provinces, and in the Severn province generally; in S. Wales not in Radnor; in N. Wales not in Montgomery, Denbigh, or Anglesea; throughout the Trent and Mersey provinces, except Mid Lancs; in the Humber and Tyne provinces, except in Cheviotland; and in the Lakes province, except in the Isle of Man. It occurs throughout the whole of the W. Lowlands; only in Berwick, Edinburgh, Linlithgow in the E. Lowlands; in the E. Highlands, only in Fife, Stirling, W. Perth, Kincardine, S. Aberdeen; in the W. Highlands, in Dumbarton and Mid Ebudes. It is rare in Scotland and local in Ireland.
The Common or Yellow Loosestrife, not so common really as the Wood Loosestrife and Creeping Jenny, is found here and there throughout the country by the sides of rivers and other tracts of running water, but owing to the drainage of the country it is less common than formerly. Other plants of this type are Frogbit, Snakeshead, Fritil-lary, and we may add the introduced Musk, which, once on the increase, is now again decreasing. It is also a plant of peaty woodland swamps, and grows frequently in ditches.
The plant is erect in habit. Usually it is downy. The rootstock is creeping, and the plant is stoloniferous. The stem is erect, rather square in section. The leaves vary greatly in size, shape, and the amount of down. In one form there are 3 leaves in a whorl, in another 4. They are, if not whorled, opposite, egg-shaped or lance-shaped, dotted. As with most verticillate leaves there are no leafstalks. There may be black glands on the leaves below, or they may be hairless or downy.
The flowers are golden-yellow with red spots at the base, in terminal or axillary panicled cymes, which are simple or compound. The corolla is more or less bell-shaped, the 5 lobes entire, egg-shaped, not fringed with hairs, without alternating teeth. The lobes of the calyx are lance-shaped, fringed with hairs, with red margins. The 5 anther-stalks are united below, and the stamens included. The capsule is round. The seeds are rough with a border, 3-angled.
Great Yellow Loosestrife is about 3 ft. in height. The flowers no bloom from July to September. It is a perennial, propagated by-division, and is worth cultivating.
There are three types of plant which have been found on the Continent. In one the flower is conspicuous, and is rarely if ever self-pollinated. This is a sun plant, occurring on embankments. In a second less conspicuous shade form self-pollination regularly occurs. In places of an intermediate character, as ditch banks, there are transitional types. None of these forms contain honey. The petals in the sun plant are dark-yellow and have red spots at the base, like honey-guides, and are expanded or bent back at the tip, the petals be-ing 12 mm. long and 6 mm. wide. The anther-stalks are also red-tipped. The anthers are included, and the style is much longer, well projecting. If an insect visits the flower it touches the stigma first and cross-pollinates the flower. In the absence of insects seed is not set, as the anthers are not level with the stigma and the flower is erect. The petals in the shade plant are of a lighter yellow. There are no red spots below. They are not so long or wide, being 10 mm. and 5 mm. respectively, nor do they expand so far, but are oblique. The anther-stalks are greenish-yellow. Here the style and the two longer inferior stamens are of equal length. Hence if the flower is not visited and cross-pollinated by insects, self-pollination may occur. In the third type the anther-stalks may be red, or the petals may be larger, or red and large. Further, the corolla may be slightly reddish at the base, and in a fifth case the style may be longer than the longer stamens. The flowers are visited by pollen-seeking insects. An insect that is especially abundant where these plants are found is Macropis labiata; where it does not occur the plants are absent. The females are abundant on the sun plant.
Photo. Flatters & Garnett - Great Yellow Loosestrife (Lysimachia Vulgaris, L.)
The flower is visited by Macropis, Halictus, Andrena, Odynerus, and a fly, Syritta pipiens. Macropis labiata is the chief visitor.
The capsule being 5-valved and many-seeded, the seeds are shaken out by the wind at the top.
Yellow Loosestrife is largely a peat-loving plant, requiring a moist peaty soil, either sandy or clayey.
Two beetles, Crepidodera salicariae, Galeruca sagittarii, two Hymenoptera, Macropis labiata, Selandria luteola, two moths, Den-tated Pug (Collix sparsata), Powdered Quaker (Taeniocampa gracilis), are found on it.
Lysimachia, Dioscorides, is from the Greek luo, loose, mache, battle, or loose-strife; and the second Latin name suggests that it is common, but this is a mistake.
Golden Loosestrife, Herb Willow, Yellow Loosestrife, Willow Herb, Golden or Yellow Willow Herb, Willow Wort, Yellow Rocket, are some of its English synonyms. The name is thus explained by Gerard: "An adaptation of the last name Lysimachia, which, as Dioscorides and Plinie doe write, tooke his name of a speciall vertue that it hath in appeasing the strife and unrulinesse which falleth out among oxen at the plough, if it be put about their yokes, but it rather retaineth and keepeth the name lysimachia of King Lysimachus, the son of Agathodes, the first finder out of the nature and vertues of this herbe, as Plinie saith".
The plant is cultivated, and is more deserving of notice than many others that are more popular at present.
Essential Specific Characters:201. Lysimachia vulgaris, L. - Stem erect, branched, leaves lanceolate, acute, sub-sessile, in whorls, opposite, flowers yellow, in terminal panicle, or axillary, stamens united.