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.
The present distribution of this common plant is the N. Temperate Zone in Europe, the Canaries, Siberia, W. Asia, and it is introduced in North America. It is unknown in early deposits. In Great Britain Purple Dead Nettle is found throughout the country, and in Northumberland ascends to 2000 ft.
Purple Dead Nettle is almost entirely a weed of cultivation, occurring freely on all kinds of waste ground, and in gardens as well as in all cultivated fields; and whilst the White Dead Nettle may be found along the roadside under hedges far from dwellings, Red Dead Nettle is more or less attached to these last or the vicinity of tilled land.
The stem is weak, suberect, square, with paired spreading branches, originating from near the base of the stem. The leaves are stalked, heart-shaped, blunt, coarsely toothed, the upper ones rather close. The stem is naked below. The foliage has a purple tinge.
The flowers are purple, in more or less terminal whorls, with many flowers, The calyx, roughly hairy, is spreading above, tubular, with five roughly-hairy teeth. The corolla is gaping, with a short cylindrical tube, inflated with a ring of hairs inside. The bracts or leaf-like organs are numerous, not overlapping, nearly stalkless. The seeds are triangular, pale-brown, included in the calyx. The plant is rarely a foot high. It flowers from May to August. It is an annual, propagated by seed.
The flower is similar to that of the White Dead Nettle, but the tube is only io-11 mm. long, and for 4-5 mm. at the top is enlarged, so that a humble-bee can insert its head. A hive-bee with a proboscis 6 mm. long can suck honey. The flowers are homogamous, the stigma and anthers ripening together. The angle between the two stigmas is less at first, and the lower stigma first stood between or above the anthers, being turned down afterwards. Before the flower opens the stigma and anthers have come in contact, and self-pollination has taken place. The hive-bee, Anthophora, Bombus, Melecta, Halictus, Bomby-lius, visit Purple Dead Nettle. The nutlets fall when ripe around the parent plant.
Photo. B. Hanley - Purple Dead Nettle (Lamium Purpureum, L.)
A clay soil suits Purple Dead Nettle, which is a clay-loving plant, or a sand soil, when it is a sand-loving plant.
Two Hymenoptera, Anthidium manicatum, Anthophora quadri-maculata, and a moth, Speckled Yellow (Venilia maculata), are found upon it.