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Dr Andy Scobie,
Project Officer

Cairngorms Rare Plants Project
Scottish Natural Heritage,
Achantoul, Aviemore,
Inverness-shire,
PH22 1QD

Tel: +44 (0) 1479 810477
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The species
Small Cow-wheat

Small Cow-wheat image panel

Description and ecology:

This small, delicate annual has bright yellow nodding flowers which occur in pairs along the main stem and side branches. The long, narrow, pointed leaves are widest about ¼ of the way from the base. Flowering occurs throughout June and July.

Small Cow-wheat is a ‘hemi-parasite’, a term which refers to its clever strategy for obtaining additional water and nutrients. Roots of Small Cow-wheat form connections with those of neighbouring ‘host’ plants, hooking into their xylem and phloem vessels, enabling them to acquire water and nutrients from the host plants. Small Cow-wheat has green leaves and photosynthesises so it is not entirely dependent upon its hosts, hence the word ‘hemi’ meaning half. Small Cow-wheat forms root connections with a wide range of plant hosts but legume hosts produce the biggest plants. In the absence of a host, Small Cow-wheat plants are much smaller and many don’t reach sexual maturity.

The flowers are insect pollinated, most likely by bumblebees, but are also capable of automatic self-pollination so seed set is high even in the absence of pollinators. Following pollination, the ovary of each flower swells and ripens to form a two seeded capsule which splits open to reveal the seeds when ripe in August.

The seeds of Small Cow-wheat are relatively large and have a small body on them called an elaiosome which is rich in fat and protein. The elaiosome is a reward for wood ants which act as seed dispersal agents. The wood ants collect the seeds directly from the split capsules and carry them back to their nests where they remove the elaiosome then deposit the seeds intact as refuse. It has been hypothesised that this relationship with ants is important for the dispersal of seed to favourable microsites for germination and establishment, such as gaps in the forest canopy where ants build their nests, and also for the avoidance of seed predation by rodents.

Being an annual, production of seed is of critical importance to the next generation and for the persistence of a population at a particular site. Seeds of Small Cow-wheat may lie dormant in the soil for up to 5 years but become inviable beyond this. Failure of the population to produce seed (e.g. following high levels of seedling or adult mortality, or grazing of adult plants before they set seed) or heavy losses of seed (e.g. via seed predation) could lead to the rapid decline and disappearance of a population in the space of only a few years.

In Scotland, the majority of remaining Small Cow-wheat populations are very small and highly isolated from one another. Recent genetic work has revealed very low levels of genetic diversity within most of these populations and a high degree of differentiation between them. This situation has arisen as a consequence of isolation of the remaining populations and a lack of gene flow between them, so inbreeding is inevitable. In the absence of gene flow, the quick turnover of generations leads to a rapid loss of genetic diversity over time and, under the action of natural selection, the gene pool becomes highly adapted to the particular site conditions.

The current situation for Small Cow-wheat in Scotland is cause for great concern. The small, isolated populations are vulnerable to random population fluctuations and stochastic events, which may lead to the disappearance of a population from a site. The large, heavy seeds have short dispersal distances so the potential for recolonisation of new areas of suitable habitat is very limited. With low levels of genetic diversity remaining populations will have limited potential to adapt to future environmental change and may ultimately face extinction in the long-term.

Flowering material is essential for the reliable identification of Small Cow-wheat. Strains of the closely related and highly variable Common Cow-wheat (Melampyrum pratense), which also have bright yellow flowers, can easily be mistaken for Small Cow-wheat even by the most experienced of botanists. Recording of Small Cow-wheat in the UK is somewhat chequered by a long history of erroneous records. However, Small Cow-wheat could equally be overlooked for Common Cow-wheat so the species may well be under-recorded in the UK. Download the Identification Guide for notes on how to identify them.

Habitat:

In the UK, Small Cow-wheat is found in upland broadleaved woodland (or former sites of) where Birch (Betula spp.) is typically the dominant tree species, sometimes in association with Rowan (Sorbus aucuparia), Hazel (Corylus avellana), Oak (Quercus spp.) and Ash (Fraxinus excelsior), on moderately acidic soils which are usually moist but free draining.

Most of the remaining populations occur in isolated wooded gullies and tree-lined ravines or high up on rock ledges, escaping from heavy grazing pressure, usually in lightly shaded north facing sites close to water bodies.

Distribution and status:

Although previously recorded from over 200 sites in Britain and Northern Ireland, Small Cow-wheat has undergone a major decline and is now restricted to less than 20 sites in the Highlands of Scotland and one or two in Northern Ireland.

Follow the links below to view a UK distribution map:
BSBI UK Distribution Map
NBN UK Distribution Map

There are only three extant sites for Small Cow-wheat in the whole of the Cairngorms National Park.

View the CNP distribution map here:
CNP Distribution Map ( PDF File )

Many of the remaining populations are very small and highly isolated. Small Cow-wheat is classified as Nationally Scarce and has been identified as a conservation priority in the UK Biodiversity Action Plan and the Species Action Framework for Scotland and is included on the Scottish Biodiversity List.

Reason for decline and current threats:

1) Loss and fragmentation of upland broadleaved woodland.

Extensive felling of woodland for timber, widespread conversion of woodland to agricultural land, and unrestricted heavy grazing of woodland habitats by deer and domestic livestock has dramatically reduced and fragmented the extent of upland broadleaved woodland in the UK and is likely to have been a major cause of decline of Small Cow-wheat.

2) Creation of dense conifer plantations.

The replanting of felled native woods with extensive areas of uniform, closely spaced trees with heavily shading canopies which are inhospitable to forest herbs such as Small Cow-wheat.

3) Lack of seed dispersal agent.

The local decline of wood ants from the areas containing the few remaining Small Cow-wheat populations has left the plant without a seed dispersal agent.

4) Inability to recolonise suitable habitat.

With large and heavy seeds, inherently low seed dispersal distances, and a lack of seed dispersal agent, the remaining small and highly isolated Small Cow-wheat populations have little prospect of recolonising new areas of suitable habitat.

5) Vulnerability of small, isolated populations with low levels of genetic diversity.

Small populations consisting of only a few hundred individuals are vulnerable to extinctions due to random population fluctuations and stochastic events. With low levels of genetic diversity these small populations have limited potential to adapt to environmental change and most certainly face extinction in the long term.

Action for Small Cow-wheat in the Cairngorms National Park:

1) Increased recording and monitoring of Small Cow-wheat in the Park.

The location of all known populations of Small Cow-wheat in the Cairngorms National Park will be established and searches 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 provide a baseline against which to measure future change.

2) Implementation of conservation action.

Considerable research has already been undertaken on this species by the Scottish Wildlife Trust and researchers at the University of Aberdeen, the Royal Botanic Gardens Edinburgh and Forest Research. A Species Recovery Project was also developed and implemented by the Small Cow-wheat National Steering Group providing important information on potential recovery strategies for the species. Utilising information from this previous research, actions will be undertaken to safeguard and expand Small Cow-wheat populations within the Park, this will include:

Habitat management and population expansion trials

  • With a particular focus on the Glen Tilt stronghold, work will be undertaken to improve the suitability of woodland habitat for Small Cow-wheat.
  • Planting trials will also be conducted within the stronghold area to expand and existing populations into areas of suitable habitat.

Translocation trials

  • The establishment, via translocation, of a new genetically diverse population in an area of suitable habitat at a site within the Cairngorms National Park.

 
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