Hempnettles are stout, untidy plants with large trumpet, shaped flowers. My reference book shows four species of British hempnettles with the red hempnettle and the large flowered hempnettle not found in Dorset so if you find a hempnettle here you have a choice of two, the bifid hempnettle and the common hempnettle (Galeopsis tetrahit). The latter two are very similar but the common hempnettle is much more common and found in a wider range of situations.
Common hempnettle can be quite variable. The flowers can be purple, sometimes a paler pink and they even come in white. e white ones are not uncommon and the first time I encountered them in Wareham Forest I was convinced it was a new species for me but after failing to find a white one in my book I then discovered that variations occur in the common! The plantsgrow to about a metre tall and tend to flop over despite their thick stems. The leaves are not dissimilar to the leaves of the stinging nettle but in the case of hempnettle do not give you a nasty surprise. The plant is quite hairy and the flower head is quite prickly, especially when in seed.
Quite often found in damp places in ditches, fens and by streams but they also can be found on heathland and arable land too. They flower from July until September. The plant is poisonous but chemicals can be extracted from it for various medicinal uses.