A rhizomatous perennial herb of lightly-shaded woodland edges and scrub overlying chalk. Lowland.
This species has been known since 1843 from a single dry chalk valley in the Isle of Wight. Although once abundant, the cessation of coppicing in the 1940s led to a marked decline, but this has been stemmed by the resumption of coppicing and the clearance of invasive ground-cover and more nutrient demanding tall herbs such as Eupatorium cannabinum and Urtica dioica.
European Temperate element.
Light (Ellenberg): 5
Moisture (Ellenberg): 5
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4.8
July Mean Temperature (Celsius): 16.3
Annual Precipitation (mm): 844
Height (cm): 60
Perennation - primary
Life Form - primary
Clonality - primary
Comment on Clonality
Count of 10km squares in Great Britain: 1
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 0
Plantatt Conservation Status
RDB Species Accounts
Clinopodium menthifolium (Host) Stace (Lamiaceae)
Calamintha sylvatica Bromf.
Status in Britain: ENDANGERED. WCA Schedule 8.
Status in Europe: Not threatened.
C. menthifolium is a plant of woodland edges and scrubby thickets on chalk. It has only ever been known as a native species in this country from a single location, a dry chalk valley on the Isle of Wight, where it was first described by William Bromfield as occurring "in the greatest profusion and luxuriance" (Bromfield 1843). The only current site is a scrubby woodland edge where there is good light and the soil contains little humus. Associated plants are those characteristic of chalk woods in this part of the Isle of Wight, including Allium ursinum, Brachypodium sylvaticum, Campanula trachelium, Rubus caesius, Stachys sylvatica and Tamus communis. More recently, the community has tended to become dominated by more nutrient-demanding tall herbs such as Dipsacus fullonum, Eupatorium cannabinum and Urtica dioica.
C. menthifolium spreads vegetatively by short creeping rhizomes. Flowering is prolific, beginning in July and generally continuing until October. The flowers are visited by bumble-bees. Large quantities of fertile seed are set, but recruitment from seed is very low. It grows well under horticultural conditions and spreads freely by seed in the absence of competition.
At its greatest extent in the nineteenth century, the plant occupied a few hectares of a single valley, but the population is now reduced to a few square metres. The historic landscape was a mixture of woodlands, downland and scrub that was maintained by free-roaming grazing animals and coppicing of hazel. Bromfield described it as "growing amongst the long herbage and under the shade of bushes, in vast quantity, for a part of the way towards the head of the vale, scattered over hill-side copses wherever there is shade and shelter sufficient." Since 1940, coppicing has declined and the hazel canopy has become dense, eliminating all the lightly shaded areas where the plant was known to occur. At this time, the adjoining lane was improved and a newly created lay-by exposed fresh chalk onto which the plant was able to spread. At the present time, it occurs along an eastward-facing woodland edge and is largely confined to two lay-bys alongside a single-track road, with a few scattered plants growing elsewhere along the road verge, over a distance of some 40 metres. By 1960, fewer than five plants remained, but following conservation management, the current population is estimated to be in the low hundreds.
Conservation management since 1962 has included the coppicing of hazel and the clearance of invasive ground cover. Though this has been successful in maintaining populations (largely through vegetative spread), it has not resulted in any significant increase. As its current sites are becoming eutrophic, competition from more aggressive species is proving to be a problem. C. menthifolium would probably benefit from the creation of freshly exposed chalk rubble slopes into which it can seed. Despite protection within and SSSI and intensive conservation effort, the plant remains endangered (Winship 1994c).
C. menthifolium occurs in most European countries, but does not extend to Scandinavia.