Seeds of destruction?
Non-native wild flower seed and British floral biodiversity
When can a plant be called native?
Non-native sources of seed
How do we know that some wild flowers are not native?
How widespread is the problem?
Trouble in store? Wild flowers on 'set-aside' land
Learning from others
Some constructive ways forward
Non-native flowers to watch
In recent years many people in Britain have been growing native wild flowers, especially from commercially available seed-mixtures. Plantlife applauds and encourages the return of vanished, well-loved and colourful members of our flora. Nevertheless, we have been concerned for a while that a proportion of plant material on sale does not represent strictly native British wild flowers. The species are mostly correct, but few widespread species are uniform and some of the plants that are being grown in Britain are not the same as native wild flowers. This booklet, based on a report by the author commissioned by Plantlife, discusses evidence to suggest that considerable quantities of wild flower seed have been imported from abroad.
Wild flower seed that is not native in origin can create a number of problems:
We are especially concerned about the potential for crossing between native and non-native wild flowers, lest we lose unique native genetic variation, a key component of plant biodiversity, already threatened by the loss and fragmentation of habitats. It is vital that we protect Britain's biodiversity, our precious and irreplaceable resource of natural genetic variation. The British flora already contains a very large non-native element, including many familiar wild flowers and trees, but the introduction of large amounts of seed is likely to have a considerable effect on the natural ecological balance and genetic variation of native species.
This booklet presents evidence that a real problem exists and that, despite the responsible attitude of many seed suppliers, the use of introduced wild flower seed in Britain is widespread. We discuss the value of our non-native flora, but at the same time stress the importance of conserving native genetic variation. Ideas are suggested for promoting the greater use of native wild flowers, including an accreditation system for suppliers. The last section of the booklet details differences between native and non-native variants of a number of common wild flowers, many of them economically important fodder crops that may be needed in the future by plant breeders. A bibliography lists books on the use of wild flowers in gardening and landscaping.
Nevertheless, some of us are concerned that a proportion of the material on sale, both seed and plants, may not represent strictly native British wild flowers. The species are correct, or they usually are, but few widespread species are at all uniform and many of the plants sold in Britain are just not the same as our native wild flowers. It is important that gardeners and naturalists be made aware of this and of the issues that arise through the use of non-native wild flowers. These require some serious thought and discussion.
There are more than 50 suppliers of wild flower seeds and plants in Britain, from the major seed houses to small companies that packet and market seeds independently. Individual distributors are often concerned about the indiscriminate sowing of wildflower seed. It is important that Plantlife and others continue to encourage such responsible attitudes amongst suppliers and growers, many of whom apparently take the matter of native origin very seriously.
We have not included a list of suppliers here, although a number are recommended by the Botanical Society of the British Isles in their leaflet "Growing wild flowers from seed".
Variation amongst wild flowers
A number of variants of widespread plants are distinct enough to be recognised by botanists (variant is a most useful word, because 'form' and 'variety' imply an actual name that is used by botanists). In fact many have been given scientific names - as forms, varieties and subspecies, even species. These distinct variants frequently occur as wild plants in specific geographical areas, often regions of Europe outside Britain. In many cases they are not native to this country and it is misleading to call them native wild flowers.
The nature of the problem
Wild flower seed that is not native in origin can have a number of consequences:
Two other consequences of the use of wild flower seed must be considered. Species introduced as contaminants of wild flower seed, especially that of non-native origin, have the potential to become weeds and the introduction of any new plant has to be taken seriously. One example is Bristly Hawks'-beard (Crepis setosa), a native of southern Europe that appears regularly on resown road-verges and elsewhere. There is also the matter of the rich pickings to be had from the illegal collection for sale of native plants from the wild. Plants in remote, rural areas are especially at risk, for example in north Norfolk, where there is extensive evidence for the pillage of woods for Bluebells and other wild flowers.
The one that concerns us here is that of crossing between native and introduced plants. This is perhaps the most significant in the longer term, for we must consider above all the protection of Britain's biodiversity - our precious and irreplaceable resource of natural genetic variation. Native biodiversity is particularly at threat today because we have fewer and more fragmented habitats for wild plants. The landscape can no longer buffer any large-scale introduction of new plants or animals.
At a time of widespread public concern about the loss of biodiversity in the tropical rain forests, it would be foolish to do anything that might put at risk our own special native plants. Many have economic use or potential; some are relatives of crop plants. Who can say when they will be needed by the plant breeder?
Let us first look at the vexed question of 'native' versus 'non-native' wild flowers.
When can a plant be called native?
Surviving habitats have mostly been reduced to small islands and strips, all too frequently surrounded by uninteresting urban, industrial or intensively farmed land. This makes the species, and their variants, that survive in such pockets vulnerable to damage by insensitive management, by building and other development and as a result of invasion by, and crossing with, alien species. They will also be susceptible to factors such as climatic change, agricultural and industrial pollution, including acid rain, and other long-term, major environmental damage.
The problems of introduced species in the wild have long been recognised worldwide, especially when they invade cultivated ground or treasured stands of natural vegetation. The classic example is the damage to the Australian outback, which became covered by thousands of hectares of an introduced cactus, Prickly Pear (Opuntiaficus-indica). In Britain, large areas of land have disappeared under thickets of Japanese Knotweed (Faliopia japonica), an aggressive invader from the Himalayas and eastern Asia, once an esteemed garden plant.
The problems posed by introduced variants of indigenous species have received considerably less attention.
Our non-native flora
Some botanists have resisted all introductions of plant species to Britain. Others take a positive attitude to introductions, recognising that these plants can make a significant contribution to our flora. So many of our wild flowers, trees and shrubs are not native, although their origins are obscured by time. Stone Age settlers introduced well-loved cornfield weeds, such as Cornflower (Centaurea cyanus) and Corn Cockle (Agrostemma githago), both of them treasured rarities today. The same people may have introduced Beech (Fagus sylvatica), and the Romans introduced Sweet Chestnut (Castanea sativa).
Other non-native trees and shrubs have been widely planted in the recent past, to become characteristic features of the countryside, notably Horse Chestnut (Aesculus hippocastanum) from Greece and Albania, now as much a part of the English scene as church, cricket and village pub. Other trees, such as Holm Oak (Quercus ilex), well established locally in southern England, and several of the attractive Southern Beeches (Nothofagus) from temperate South America, already growing wild in the Quantock Hills of Somerset and elsewhere, will be just as familiar in time.
Fewer examples have been recorded of the deliberate introduction of individual annuals and herbaceous perennials, i.e. the plants known collectively as 'wild flowers'. However, a number of species have arrived as crop plants and have escaped into town and countryside. Many crop plants are distinct variants of native species and the crop itself may also become established in the wild. Garden plants too, especially the denizens of the traditional cottage garden, are established in the wild, not only around villages and on roadsides but also beside rivers and in woodland, adding colour and variety to our flora and landscape.
Striking examples, which have come to be regarded by most people as native wild flowers, include Himalayan Balsam or Policeman's Helmet (Impatiens glanduhfera) and several species of Monkey-flower (Mimulus), Comfrey (Symphytum) and Mullein (Verbascum). Some of these are invasive - and a few such as the notorious Giant Hogweed (Heracleum mantegazzianum) can be a menace – but they are for the most part welcome. One garden introduction in particular that has improved the landscape is the delicate, creeping Slender Speedwell (Veronica fihformis), a native of the Caucasus. In early May, grassy places and lawns shimmer with its thousands of tiny blue flowers, in part making up for grassland flowers lost through intensive agriculture.
Wild flowers in gardens and for amenity
The large-scale cultivation of wild flowers is a recent phenomenon, which seems to have begun in Holland shortly after the Second World War. There, as in Britain, the movement arose as a reaction to the loss of natural habitats in a densely populated country with intensive agriculture. The last 15 years have seen an extraordinary expansion of the wild flower seed industry in Britain, much of it following the publication in 1981 of the Nature Conservancy Council's booklet, Cicating attractive grasslands using native plant species. Conservation, wildlife gardening, the creation of new habitats and the use of wild flowers in amenity landscaping have become fashionable, promoted by the influential horticulture industry and the media.Plantlife applauds this interest and awareness of our wild flora, but not only must we consider the many effects that our enthusiasm may be having on existing native plant communities, but also establish the source of seed and plants.
Non-native sources of seed
"The seed of wildflowers is increasingly easy to come by, but ... foreign stock is widespread. This can be quite a serious problem, as the foreign strain of some of our wildflowers is much more vigorous than the native type, and could well overwhelm the indigenous stock. The responsible seedhouses are very particular about this point" our italics.
Despite the good intentions of many seed suppliers and those promoting the use of wild flowers, it has become apparent that much of the seed being distributed in Britain is not of native origin. As long ago as 1969, a non-native variant of Bird's-foot Trefoil (Lotus corniculatus), apparently a native of the southern Alps, had been reported from road-verges in Denmark and other parts of northern Europe. This and non-native variants of other plants were widely sown in Britain from the early 1970s. Botanists expressed concern about possible effects on the genetic constitution of the flora, and some preliminary research was carried out on the interaction between native and non-native variants of Bird's-foot Trefoil.
In 1989, the late Dr John Dony raised the matter of introduced wild flower seed in an impassioned plea at an Annual General Meeting of the Botanical Society of the British Isles. Based on his experience of recording the flora of Bedfordshire, he stated that the deliberate use of wild flower seed, especially of foreign origin, would render pointless the task of the botanist attempting to record the distribution of native wild flowers.
How do we know that some wild flowers are not native?
If you look at a site that has been sown with wild flower seed, have a closer look at some of the common species such as Bird's-foot Trefoil. Note whether or not the plants are robust, tall and erect; are the flowers the same colour as you normally see in this species? Similarly, Kidney Vetch: are plants unusually robust and erect and are the leaflets different in shape to the plant of chalk grassland? If Salad Burnet is present, and in fruit, have a look at the fruits - perhaps they are unusually warty. It is these sort of distinguishing differences between plants that attract the eye of the botanist interested in variation within species.
The botanist will then look through the various available Floras, new and old, to identify which variety, subspecies or distinct variant that he or she may have seen. The Flora should also indicate the native range of the plant. Again and again, we have found that too many wildflowers sown in Britain clearly originate in other parts of Europe. Sometimes we can be reasonably precise. It would seem that every plant of Kidney Vetch sown on roadsides in Britain belongs to a subspecies (indeed a variety of that subspecies!) that is native to the valleys of the Alps and other mountains of central Europe. Meanwhile, the native plant is now scarce over much of lowland Britain.
Evidence from life-history
Evidence from seed testing
Some seed is known to have been grown on in this country from plants raised from imported seed. This material is no more British in origin than "British Sherry", even though it can legally be termed native wild flower seed.
Evidence from seed suppliers
How widespread is the problem?
Examples are everywhere: from the Brixton gardener interviewed on BBC2' s Gardeners World, disappointed that the White Clover in his urban wild flower garden was "agricultural", to the robust variants of common wild flowers that can be purchased in pots at a range of horticultural outlets. One seed-mixture distributed by conservationists as part of a package to attract bumblebees contained a huge variant of Red Clover, but mercifully most of the seed of the other species included failed to germinate!
Two notable examples illustrate that even prestigious conservation projects are at risk from non-native seed.
Magog Trust, Cambridge, 1991-2
These included Cornflower (Centaurea cyanus), many of horticultural origin, with pinkish-purple flowers, Corn Marigold (Chrysanthemum segetum), rarely found on the chalk, a southern European subspecies of Hawkweed Oxtongue (Picris hieracioides), Fodder Burnet (Sanguisorba minor subsp. muricata) instead of the native Salad Burnet (S. minor subsp. minor, which grows nearby, and agricultural Red Clover (Tnfolium pratense var. sativum).
The most astonishing discovery at this site was St Martin's Buttercup (Ranunculus marginatus var. marginatus), closely related to the native Hairy Buttercup (R. sardous). This species is native to a large area from Albania to Iran, and has previously been reported from Britain only as a rare casual. R. marginaflis var. tracliycarpus, with warty rather than smooth fruits, persisted as a weed for many years on St Martin's in the Isles of Scilly. This obscure plant has recently turned up at another site, this time in the north of England, that had been landscaped with wildflower seed. In both cases it was undoubtedly the 'buttercup' or 'bulbous buttercup' included in the seed-mixture.
Garden Festival Wales, Ebbw Vale, 1992
Perhaps the most distinctive plant in the sward was Flattened Meadow-grass (Poa compressa), used with Rye-grass, (Lolium perenne) as the basis of the sward. Flattened Meadow-grass is, however, a rather scarce plant over much of Wales. The most abundant and prominent plant was Fodder Bird's-foot Trefoil (Lotus corniculatus var. sativus), with clumps of weakly erect stems 40-60 cm. An observant visitor, overheard as she walked past, remarked: "That doesn't look like ordinary Bird's-foot Trefoil"! No it did not, but a few hundred metres away, adjacent to the Festival Farm, was an attractive, established pasture of mixed grasses, native Bird's-foot Trefoil, Red Clover and Self-heal. Here one could observe that the native plant is much neater and more prostrate in habit. Also, in the main body of the Festival itself were a few square metres of wildflower-rich grassland planted by means of turves, as part of the National Trust's landscape exhibit. This grassy patch contained native variants of both Bird's-foot Trefoil and Oxeye Daisy.
However, of the three clovers used in the Wild Flower Meadow, Alsike, Red and White, only the Red Clover was the gross forage variant (Trifolium pratense var. sativum). A handsome variant of Hardheads or Knapweed (Centaurea nigra), with long ray florets, that was present does not usually occur in Wales. The Oxeye Daisy used was the robust garden hybrid, Leucanthemun x superbum. More unusual constituents of the sward were plants of Yellow Chamomile (Anthemis tinctoria) and one of the long-headed species. Neither plant is a native but both are widespread in central Europe. They are likely to have been contaminants in the seed-mixture, supporting the suspicion that at least some of the seed had come from central or southern central Europe. The two members of staff at the nearby Countryside Centre exhibit were surprised, and not a little disappointed, when I discussed the meadow with them - for they had assumed that it represented a native sward - but details of the seed sources requested at the Garden Festival office were never forwarded. Clearly, a large amount of non-native wildflower seed is being used in Britain, even for conservation projects. Clovers and other peaflowers are a particular problem because they are readily available as agricultural seed. These form an important group because their native populations represent a genetic resource of inestimable potential value. Not only are agricultural clovers frequently recommended by experts for land restoration and landscaping, but considerable sums of money are currently available to bodies such as the Department of Transport for landscape planting.
Trouble in store? Wild flowers on 'set-aside' land
Several commentators have suggested that wildflower seed might be used to beautify otherwise sterile landscapes, as well as providing food for insects such as butterflies and bumblebees, and one alternative to set-aside might be the creation of broad, wildlife-rich field margins. This has been tried locally on an experimental scale and is recommended by the Game Conservancy and others. Wildflowers sown on field margins have been shown to slow the rate of growth of noxious field weeds. However, this sort of project on a large scale might cause considerable problems for the long-term interpretation of our flora and trivialise our landscape and floral heritage.
Learning from others
Can we learn from other European countries?
In Scandinavia, the Nordic Council of Ministers has established a Nordic Gene Bank to conserve both native and introduced genetic resources in Scandinavia and Iceland, especially populations of native forage grasses and clovers. It is worth considering the Council of Europe's Recommendation on the introduction of non-native species, adopted by their Committee of Ministers in June 1984, that the governments of member states:
"prohibit the introduction of non-native species into the natural environment", except where a study to evaluate the possible consequences of such introduction has been carried out; and that member states "take the necessary steps to prevent as far as possible the accidental introduction of non-native species".
We are not always dealing with distinct species when we consider non-native wild flowers, but surely the principles should be the same?
The problem of alien versus native variants of species in our flora will become even more significant when genetically manipulated organisms are released into the wild. Almost no thought has been given to this issue in Britain, although in Holland a report has been prepared by geneticists and field botanists on the possible impact on the native flora of gene-flow from cultivated plants. In the U.S.A., where there is a long tradition of seeding road-verges with native wild flowers (especially each State's official flower), there is more discussion of 'restoration ecology' and the whole approach to wild flowers is more sophisticated, with discussion of the practical and aesthetic issues.
Are we just too haphazard, whimsical and irresponsible in Britain?
Some constructive ways forward
It is essential that native seed of local provenance be used in this sort of project, which cannot be achieved by the use of a standard commercial seed-mixture! All over Britain there are surviving pockets of ancient grassland and other plant communities that can be carefully conserved, restored and expanded.
Suppliers show the way
It is important that all of us, public and private sector conservation organisations, seed suppliers, botanists, naturalists and the many users of wild flower seed come together to discuss these issues. A step in this direction is the Wild flower Seeds Working Group.
The Wild Flower Seeds Working Group
Discussion has centred on the creation of a national seed-bank of widespread species, with collections included from all parts of Britain. Eventually the Wild Flower Seeds Working Group would like to see an accreditation system for suppliers who distribute native seed. These measures would go some way towards limiting the actual and potential damage to Britain's biodiversity that the present unrestricted use of seed is creating.
In this way, we shall be able to encourage the greater use of native wild flower seed, to bring back the floral carpets that once brightened our landscape. Any work of restoration, be it a painting, a building or a habitat, needs careful thought and discussion. Let us all consider the implications of the quality of wild flower seed and do our best to conserve our most precious, beautiful and irreplaceable natural resource, our biodiversity.
Non-native wild flowers to watch
It is probably significant that many non-native wild flowers, especially peaflowers or legumes, are readily available from agricultural suppliers. Their frequently tall, erect habit reveals their a history of selection as fodder crops, since it makes them easier to cut, either by scythe or machinery. Few of them, apart from Red and White Clover, continue to be grown as fodder crops in Britain, although they are still grown in other parts of Europe and elsewhere.
Red Clover (Trifolium pratense)
White or Dutch Clover (Trifolium repens)
Black Medick (Medicago lupulina)
Bird's-foot Trefoil (Lotus corniculatus)
Fodder Bird's-foot Trefoil has been widely used in seed-mixtures for roadside verges in Britain since the mid-1970s and has recently been reported from Ireland. Its use in wildflower seed-mixtures is partly a result of the limited availability of native seed and also an EC regulation that only approved sources of seed of agricultural species may be used commercially.
Kidney-vetch (Anthyllus vulneraria)
An unsuitable coastal variant of Kidney Vetch, with much-branched stems, is sometimes sold by nurseries. In many parts of lowland Britain, native Kidney Vetch is now rare, and it would be a pity for it to be replaced by non-native plants. In Scotland and Ireland there exists yet another subspecies of this variable plant, and on coasts of western Britain there is a rare and unique subspecies that grows on cliffs and sand-dunes.
Sainfoin (Onobrychis viciifolia)
Salad Burnet (Sanguisorba minor)
Oxeye Daisy (Leucanthemun vulgare)
Yarrow (Achillea millefolium)
Corn Marigold (Chrysanthemum segetum)
One non-native variant of a grass, in particular, has attracted the attention of several botanists. We have seen and come across several records of a robust variant of Yellow Oat-grass (Trisetum flavescens), 80-100 cm tall, that is distinct from the native plant and probably comes from S.E. Europe. This may well become a problem in restored chalk grassland, where the native plant would be appropriate.
We are grateful to Bob Flood (NIAB, Official Seed Testing Station) for data on seeds coming into Britain. We are pleased to record the assistance of Botanic Gardens Conservation International (BGCI), Kew, who provided the author with office facilities for a period during the compilation of this booklet. Plantlife is indebted to English Nature for their generous funding of this project.