This evergreen perennial herb of pinewoods and dry heath has distinctive round, stalked leaves arranged in loose rosettes. The rosettes often occur in small clusters or patches, many of which may be derived from vegetative reproduction via the shortly creeping rhizomes. The leaves are evergreen, and easily recognisable at any time of year, hence the name ‘wintergreen’.
Flowering occurs from late June to the end of July when a tall flowering spike (up to 30 cm) is produced with a loose cluster of white/pink globe-shaped flowers at the top. The flowers are pollinated by a specialised mechanism called ‘buzz-pollination’, whereby visiting bumblebees must vibrate the flower at a certain frequency to shake pollen from the vessel-like anthers. The flowers also possess a late-acting automatic self-pollination mechanism which ensures that the stigma receives some pollen from anthers in the same flower, even if the flower is never visited by an effective pollinator.
Following pollination, the ovary of each flower swells and ripens to form a dry capsule which splits down the sides. Each capsule contains several thousand dust-like seeds which are released during September and dispersed by wind. Intermediate Wintergreen is mycorrhizal and forms associations with a wide range of fungal host species. The species has been shown to be capable of vegetative re-generation from buds on the underground rhizomes after fire. Intermediate Wintergreen is a coloniser of open, disturbed ground which appears to be important for establishment and spread.
There are five different wintergreen species in the UK, three of which (Common Wintergeen, Intermediate Wintergreen and Round-leaved Wintergreen) are closely related, similar in appearance and often mistaken for one another. Floral characters, in particular the length and shape of the style, are by far the easiest and most reliable way to tell them apart but wintergreens are often shy-flowering and identification of vegetative plants can prove problematic. However, recent new methods have been developed to overcome this problem. Download the Identification Guide for notes on how to identify them.
Intermediate Wintergreen is found in ancient Scots Pine (Pinus sylvestris) woodland and pine plantations, Bearberry (Arctostaphlos uva-ursi) heathland, Birch (Betula spp.) woodland and Juniper (Juniperus communis) scrub and is usually restricted to drier, well-drained soils within these habitats.
Typical associates include: Heather (Calluna vulgaris), Blaeberry (Vaccinium myrtilus), Cowberry (Vaccinium vitis-idaea), Bearberry (Arctostaphylos uva-ursi), Wavy Hair-grass (Deschampsia flexuosa), Common Cow-wheat (Melampyrum pratense), Tormentil (Potentilla erecta), Heath Bedstraw (Galium saxatile), and pleurocarpous mosses (including: Hylocomium splendens, Pleurozium shreberi and Rhitidiadelphis triquetris).
In woodlands and unmanaged heathlands Intermediate Wintergreen typically occurs in small high density populations on the edges of forest tracks, footpaths, animal tracks, open rocky areas and the eroded banks of river gullies. However, in heathland sites managed by rotational muirburn or moderately grazed by cattle, sheep and/or deer, extensive low density populations are more typical and these are often very large. This pattern of distribution suggests that an open disturbed field layer, such as that created grazing animals, exposure or fire, is important for the establishment, persistence and spread of Intermediate Wintergreen.
The species has undergone a considerable decline in the UK being lost from 42% of pre-1970’s 10 km squares.
Widespread in the highlands of Scotland, very restricted elsewhere. The Cairngorms National Park is the UK stronghold.
Intermediate Wintergreen is widespread in the Park with a concentration of sites along Strathspey and Deeside. This species is most definitely under-recorded.
View the CNP distribution map here:
CNP Distribution Map ( PDF File )
Intermediate Wintergreen has been identified as a conservation priority in the Species Action Framework for Scotland and is included on the Scottish Biodiversity List.
1) The loss and fragmentation of native pinewoods.
Following centuries of exploitation for timber and widespread heavy grazing by deer and domestic livestock, the natural pine forests that once covered much of northern Scotland have been reduced to a few isolated and degraded fragments. This is clearly bad news for pinewood plants such as Intermediate Wintergreen.
2) Unsuitable woodland and heathland management.
Creation of dense plantations:
The replanting of felled native pinewoods with extensive areas of uniform closely spaced trees, or the encouragement of dense natural tree regeneration, with a heavily shading canopy suppressing the growth of understory plants below, including Intermediate Wintergreen.
Inappropriate grazing levels:
The heavy grazing of pinewoods and heathlands by deer and domestic livestock leading to the ‘grazing out’ of herb species such as Intermediate Wintergreen. The under grazing of open pinewoods and heathlands leading to the development of tall and dense shrub growth, in particular heather (Calluna vulgaris), which can potentially shade out Intermediate Wintergreen.
Abandonment of traditional muirburn:
In contrast to Twinflower, Intermediate Wintergreen is well adapted to cope with low intensity heather burning and persists and spreads in the open, disturbed conditions created by this form of management. Abandonment of traditional muirburn practice is likely to have caused the decline of Intermediate Wintergreen at certain sites. However, there are still extensive areas of heathland managed for red grouse in certain areas of the Park providing suitable habitat for Intermediate Wintergreen.
Lack of natural disturbance:
Natural forest fires, the impact of roaming herds of grazing animals, and windthrow are likely to have been important for the creation and maintenance of open, disturbed habitat in natural forest systems promoting the establishment and spread of herbs such as Intermediate Wintergreen. The balance of these natural processes is now disrupted and often highly manipulated in many forests today and disturbance levels are often very low.
1) Increased recording and monitoring of Intermediate Wintergreen in the Park.
The location of all known Intermediate Wintergreen populations will be established, increased recording of the species will be encouraged, and searches will be conducted at historical sites and in areas of suitable habitat. Accurate GPS location data and basic monitoring data will be collected at all sites. This data will be used to inform land managers of the presence of Intermediate Wintergreen populations on their land and to provide a baseline against which to measure future change.
2) Surveys of key sites to establish conservation issues and identify appropriate action.
Detailed surveys of Intermediate Wintergreen populations will be undertaken at key sites in the Cairngorms National Park to increase knowledge and understanding of the requirements of the species and identify current habitat constraints.
3) Implementation of conservation action.Information from these surveys will be utilised to advise land managers on targeted habitat management to promote the establishment, persistence and spread of Intermediate Wintergreen. Experimental management trials with appropriate long-term monitoring will be set-up to test management actions and these will include:
Localised habitat management
- Management of ground-layer vegetation within the proximity of existing populations to create open, disturbed habitat to promote the persistence and spread of Intermediate Wintergreen (including actions such as brush-cutting, heather burning and disturbance of the moss layer).
Larger scale habitat management
- Management of the pinewood and heathland ground layer vegetation on the large scale to create suitable open, disturbed habitat to promote the establishment and spread of Intermediate Wintergreen and other pinewood herbs (including actions such as brush-cutting, heather burning, seasonal cattle grazing).
- Localised canopy thinning/re-structuring to increase the structural diversity of plantation woodland creating niches for Intermediate Wintergreen and other pinewood herbs.