Pennyroyal (Mentha pulegium)

GenusMentha (1)
SizeHeight: 10 - 40 cm (2)

Classified as Vulnerable in Great Britain (3), and fully protected in the UK by Schedule 8 of the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders 1985 (4).

Pennyroyal is a creeping plant that has small, elliptical leaves in opposite pairs on the stem. The lilac to pinkish-purple coloured flowers are arranged in tightly-packed whorls down the stem (2), which have been likened to pin-cushions (5). The plant gives off a distinctive peppermint-like aroma (2).

This native species has experienced one of the worst declines of any UK plant. It was formerly recorded from throughout much of lowland England and Wales, but is now known only from a few sites, such as the New Forest in England, and the shores of Loch Beg in Northern Ireland (6). However, it seems to be increasing as an introduction, and has been widely recorded as such in southern Britain (6). It also occurs throughout much of Europe, where it is not threatened, but is known to be in decline in a number of countries (4). It has been introduced to North America (7).

Inhabits seasonally-flooded damp grasslands and is usually associated with the edges of temporary pools (3). The habitats supporting this species tend to have very short grass, and experience grazing or disturbance throughout the year (3). Examples of this habitat type are lowland village greens with traditional management, and the edges of unmetalled tracks (3). It is also occasionally introduced to sites such as roadsides and coal tips with grass seed from America (6).

Pennyroyal is a perennial plant that flowers from June to October (2). Although the flowers seem to set seed well, and are self-compatible, seedlings have rarely been observed in the wild, and the plant tends to spread by rooting from the stems (3).

This species was thought of as something of a 'cure-all'; it was a common feature of cottage gardens and was used as a treatment for many ailments including colds, and as a flea repellent. Indeed, the Latin name pulegium was given to the plant by the Romans who knew that the leaves kept the flea Pulex at bay (5).

The widespread loss of seasonally wet habitats preferred by this species, abandonment of traditional management techniques, and agricultural intensification including chemical fertiliser and herbicide use, are all responsible for the decline of this species (4).

Pennyroyal is a UK Biodiversity Action Plan priority species. The Species Action Plan aims to maintain the current range, and to restore the plant to five historic sites before the year 2003 (4). The development of an ex-situ population has also been proposed in order to provide a source for potential future reintroductions and to protect genetic diversity (4).

See also the BSBI website:

Information authenticated by Tim Rich of the National Museums and Galleries of Wales.

  1. National Biodiversity Network Species Dictionary (March, 2002)
  2. Press, B. and Gibbons, B. (1993) Photographic field guide: Wild Flowers of Britain and Europe. New Holland Ltd., London.
  3. Wigginton, M.J. (1999) British Red Data Books 1; Vascular Plants. 3rd Edition. JNCC, Peterborough.
  4. UK BAP Species Action Plan (March, 2002)
  5. Fisher, J. (1987) Wild Flowers In Danger. H. F. and G. Witherby, Ltd., London.
  6. Preston, C.D., Pearman, D.A. and Dines, T.D. (2002) New Atlas of the Flora of Britain and Ireland. Oxford University Press, London.
  7. Briggs, M. (1997) Non-native Mentha pulegium (Pennyroyal). BSBI News, 74: 50 - .