Red deadnettle (Lamium purpureum)
Height x spread: 15-30 x 15cm (6-12 x 6in).
Leaves: Oval, edges serrated, often tinged purple, up to 5cm (2in) long.
Flowers: Pinkish purple, hooded, 1-1.5cm (3/8-5/8in) long, in rings at upper leaf joints, spring to mid autumn.
Other features: Stems hairy, square in section. Annual.