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 plant is found in Late Glacial beds at Twickenham, Neolithic and Roman beds deposits at Silchester. At Twickenham it was associated with Reindeer, Bison, and Bos longifrons, but not extinct animals, suggesting a transition period between Palaeolithic and Neolithic. It is found to-day in the Arctic and Temperate Zones in Arctic Europe, N. Asia, W. Asia, to N.W. India, and is introduced into N. America. It is found in all parts of Great Britain, up to 1300 ft. in Northumberland. Watson regarded it as native or a colonist.
Hemp Nettle is found by the roadside, and in hedgerows, generally in the shade, and is frequent on the borders of cornfields, where perhaps it is most at home. But it is also to be found along other hedgerows in fields. It occurs again in waste places, suggesting it is largely a weed of cultivation.
Tall-stemmed and erect, the plant is well distinguished if only by its long, dense bristles. The stem joints are thickened above,1 the leaves are hairy, egg-shaped, acute, notched, shortly stalked, with opposite branches.
The flowers are in dense whorls and white or purple or yellow. The calyx-teeth are long and come to a point, or are awl-shaped. The tube of the corolla is slightly expanded. The nutlets are large, green, and veined.
Hemp Nettle is 2 ft. high. The flowers open in July and August. It is an annual plant, propagated by seeds.
The tube is from 11 - 17 mm. long. The upper part for 4 - 6 mm. is expanded so that long-lipped bees can reach the honey. When fully developed the pistil lengthens. The honey is contained in the swollen base of the ovary, and lies in the smooth part of the tube which obliquely ascends. The corolla is divided into an upper lip which is arched over, covering the anthers, and a lower lip, trifid, for alighting, which has honey-guides or yellow spots with a network of red lines. There are two convex pouches in the sides of the lower lip which help a bee to insert its head. The anthers like boxes with a closed lid open before the flower opens, with their pollen-covered surface downward. The style, which is bilobed, lies behind and above the anthers at first, the upper lobe being warty, the longer bent up. The bee in a younger flower first touches the anthers with its back, and then the papillose or warty stigma. Usually the bee's back touching the stigma lies between spots dusted with pollen in the same flower. The end of the style curves down, and the lower division projects between the anthers, and if the pollen is not removed it is then self-pollinated.
1 These act as pulvini and are connected with sleep movements.
Hemp Nettle is visited by the Hymenoptera Bombus, Andrena, Melano-stoma.
The nutlets, which are slightly netted, when ripe fall around the parent plant.
Hemp Nettle is a clay plant growing on clay soil, or a sand plant growing on sand soil.
Several beetles, Meli-gethes viduatus, M. ovatus, Chrysomela menthastri, C. fastuosa, a moth, Lygris aIchemillata, a Hemipter-ous insect, Eysarcoris melanocephalus, and a fly, Chromatomyia albiceps, are found on it.
Galeopsis, Dioscorides, is from the Greek gale, a weasel, and opsis, appearance, because the top of the flower is like a weasel's snout. Tetrahit, Dillenius, is from the Greek word for four, because of the four-angled stem.
The plant is called Bee-nettle, Blind Nettle, Dai-nettle, Day-nettle, Dea-Netle, De-Nettles, Deye- Nettle, Dog Nettle, Donnine-thell, Female Hems, Glidewort, Bastard Hemp, Hemp-Nettle, Holyrope, Nettle Hemp, Stinging Nettle, Sting Nettle.
Photo. H. Irving - Hemp Nettle (Galeopsis Tetrahit, L.)
The names Day-nettle, Deye-Nettle are derived from the injurious effects of the plant, which stings severely, upon reapers.
Essential Specific Characters: 257. Galeopsis Tetrakit, L. - Stem erect, hirsute, branched, swollen at the joints, leaves ovate, serrate, hispid, flowers white, or rose, in dense whorls, with long subulate calyx-teeth, corolla-tube as long as the calyx.