T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Prunella vulgaris (Selfheal)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Lamiales
Family: Lamiaceae
Genus: Prunella
Species: P. vulgaris
Binomial name: Prunella vulgaris
Common names: Selfheal  Common selfheal, Heal-all, Heart-of-the-earth,  Woundwort

Selfheal is a perennial weed with a creeping stem which allows it to form dense mats within lawns and can grow up to  5–30 cm in waste areas. It is typically found in moist to wet soils but can also tolerate dryness. Its tolerance of many selective turf herbicides also helps to make it a problem weed. It forms large patches of dark green leaves made up of creeping stems that have roots holding them to the soil and leaves in opposite pairs along these stems. 
The ascending-erect stem's base is branched. It is 4-edged, sparsely short-haired along the edges, it is usually partly purplish.
The leaves tend to be slightly larger in size than those of pennyroyal, another member of the Lamiaceae family often found forming dense mats in moist lawns. When the leaves of pennyroyal are crushed, a strong mint smell is given off, which doesn't happen with Selfheal.

It has quite large flower heads at the end of each stem, which is composed of successive layers of dark blue flowers forming on top of each other. Once flowering has finished, the seed-head goes brown. In contrast, pennyroyal has its flowers at the base of leaves, rather than at the ends of stems.

As suggested by its name, it has been claimed to have properties which allow people to "heal themselves," being originally used to treat external wounds, and nowadays used for helping heal bruises and an infusion is taken by some people to heal a number of ailments. For medicinal purposes, the whole plant is gathered when the flowers bloom and dried. The leaves and small flowers of heal-all are edible.  
For more information  re its health properties  http://www.herbs2000.com/herbs/herbs_self_heal.htm  

A young flower


The 4-edged stem with sparsely short-hairs along the edges. Photo shows the hairy underside of a leaf

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/