It grows to 5–20 cm (rarely 30 cm) in height. The leaves have fine hairs, are green at the bottom and shade to purplish at the top; they are 2–4 cm long and broad, with a 1–2 cm petiole (leaf stalk), and wavy to serrated margins.
The zygomorphic flowers are bright red-purple, with a top hood-like petal, two lower lip petal lobes and minute fang-like lobes between.They may be produced throughout the year, including mild weather in winter. This allows bees to gather its nectar for food when few other nectar sources are available. It is also a prominent source of pollen for bees in March/April (in UK), when bees need the pollen as protein to build up their nest.
It is often found alongside Henbit Deadnettle (Lamium amplexicaule), which is easily mistaken for it since they both have similar looking leaves and similar bright purple flowers; they can be distinguished by the stalked leaves of Red Deadnettle on the flower stem, compared to the unstalked leaves of Henbit Deadnettle.
Though superficially similar to a nettle in appearance, it is not related and does not sting, hence the name "deadnettle".
Young plants have edible tops and leaves, used in salads or in stirfry as a spring vegetable. If finely chopped it can also be used in sauces.
Undyed, the pollen itself is a red colour.
The essential oil is characterized by its high contents of germacrene D. The seed oil contains 16% of an acid characterized as (−)-octadeca-5,6-trans-16-trienoic acid (trivial name `lamenallenic acid'). Other unsaturated esters identified by their cleavage products are oleate, linoleate and linolenate.
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- Composition of the essential oils and in vivo emission of volatiles of four Lamium species from Italy: L. purpureum, L. hybridum, L. bifidum and L. amplexicaule. Guido Flamini, Pier Luigi Cioni and Ivano Morelli, Food Chemistry, June 2005, Volume 91, Issue 1, Pages 63–68, doi:10.1016/j.foodchem.2004.05.047
- An octadecatrienoic acid from Lamium purpureum L. seed oil containing 5,6-allenic and trans-16-olefinic unsaturation. K. L. Mikolajczak, Mary F. Rogers,* C. R. Smith, Jun. and I. A. Wolff, Biochem J., December 1967, volume 105, issue 3, pages 1245–1249, PMC 1198447
- Five new phenylethanoid glycosides from the whole plants of Lamium purpureum L.. Nanoko Ito, Tamotsu Nihei, Rie Kakuda, Yasunori Yaoita and Masao Kikuchi, Chem Pharm Bull (Tokyo), December 2006, volume 54, issue 12, pages 1705-1708, PubMed
- cDNA cloning and functional characterization of flavonol 3-O-glucoside-6″-O-malonyltransferases from flowers of Verbena hybrida and Lamium purpureum. Hirokazu Suzuki, Toru Nakayama, Shiro Nagae, Masa-Atsu Yamaguchi, Takashi Iwashita, Yuko Fukui and Tokuzo Nishino, Journal of Molecular Catalysis B: Enzymatic, 4 May 2004, Volume 28, Issues 2–3, Pages 87–93, doi:10.1016/j.molcatb.2004.01.005