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.
Hemp Agrimony can lay good claim to being a native British species if only from its discovery in Interglacial, Late Glacial, and Neolithic beds. To-day it is found throughout the Temperate Northern Zone in Europe, Siberia, as far east as Japan, Western Asia, as far as the Himalayas, and in North Africa. In Great Britain it is not found in Cardigan, Mid Lancs, Linlithgow, Stirling, Mid Perth, N. Perth, N. Aberdeen, Banff, E. Sutherland, and in North Wales.
Hemp Agrimony is usually a hygrophyte, preferring the damp surroundings of a hollow near a lake or stream, often seeking further the shelter and humid atmosphere of a damp copse. But it is to be found in hedgerows at a distance from water occasionally, on the borders of cornfields.
This is a tall, handsome species, growing usually in clumps. The stems are reddish, erect, and the leaves opposite, shortly stalked, 3- or 5-lobed, with lance-shaped segments which are deeply and coarsely toothed. The radical leaves are stalked, the stem - leaves nearly stalkless.
The whitish-lilac flowerheads are in terminal corymbs, tufted, containing few (5-6) crowded flowers. The phyllaries or involucral bracts are short and blunt. The florets exceed the involucre in length. The pappus or hair is roughish, white. The fruit or achene is angled.
The plant grows to a height of 3 ft. or more. It is a late-flowering species, blooming in August and September. It is a deciduous, herbaceous perennial, which is multiplied by division.
The flowerhead is a capitulum of 4 or 5 or 6 florets. The tube is 2 1/2 mm. long, with a wider throat or bell. Though each capitulum is small, as they are numerous they together form a large head. The bracts of the corolla are red-bordered, and the corolla red, with white projecting stigmas. The corolla is 5 mm., and the style divided its whole length, with rows of stigmatic wart-like projections along the margin a quarter of the length, and for the rest clothed with hairs. The anthers ripen first on the inside, and pollen fills the tube. In the first stage the lower part of the branches of the style remains enclosed in the cylinder formed by the anthers, which does not project beyond the corolla. The ends of the style with hairs project beyond it, and carry pollen with them, spreading so much that insects touch them all round, and carry off on their coats pollen entangled in the hairs of the style. After the lower papillae emerge from the cylinder and the root of the corolla they spread so far apart that an insect must touch them in visiting the flower. If sufficient insects have visited them to clear the pollen away before the stigmas are exposed or receptive, the plant is cross-pollinated, but if pollen is left when the stigmas are exposed an insect may self-pollinate it. Even if no insects visit it cross-pollina tion may follow, styles and stamens of neighbouring florets coming in contact. It is visited by Apis, Bombus, Eristalis, Echinomyia, Dexia, Luc ilia, Pieris rapae, Thecla quercus, Lycaena, sp.; Peacock (Vanessa-10), Silver-washed Fritillary (Argynnis paphia), Marbled White (Melanargia galatea), Speckled Wood (Pararge egeria), Hesperia, sp.; and a Neuropterous insect, Panorpa.
Photo. H. Irving - Habit And Habitat
Photo. Matson - Flowerhead (Nat. Size) Hemp Agrimony (Eupatorium Cannabinum, L.)
The achenes are provided with a pappus, and the fruit is angled and adapted for wind dispersal.
Hemp Agrimony is a semi-aquatic plant, which is partly a humus-or peat-loving plant, and requires humus, and partly a clay-loving plant living on a clay soil, the moisture requirements regulating the rock-soil habitat.
Two beetles, Anaspis frontalis, Longitarsus flavicornis, and the Lepidoptera, Burnished Brass (Plusia chrysitis), Botys lancealis, Con-chylis rupicola, Coleophora troglodytella, Pterophora microdactylias, Dictopteryx shepherdana, and the flies, Chromatomyia albiceps and Trypeta zoae, can be found on it.
Eupatorium, Dioscorides, is from Eupator, a name of Mithridates, King of Pontus, and cannabinum means hempen.
It is called Bastard Agrimony, Dutch, Hemp, and Water Agrimony, Andurion, Filaera, Hemp, Bastard and Water Hemp, Hemp-weed, Raspberries and Cream.
Essential Specific Characters:150. Eupatorium cannabinum, L. - Stem erect, rough, reddish, leaves downy, opposite, leaflets 3-5-cleft, lanceolate, serrate, flower-heads lilac or reddish, in a terminal corymb, with long, deep, divided styles, pubescent, pappus pilose.