Fifteen common species of the pea family, the Leguminosae, occur with grasses in Britain's fields hedgerows, and roadside verges. They range from large shrubs, such as gorse, to very small-flowered clovers, which dominate weedy lawns. Evolution in South West Europe has produced about 55 different groups, (the genera), most of which only occur in Spain and Portugal. The clovers of the genus (Trifolium) have a particularly high biodiversity, with about 50 species living in southwest Europe alone.

Domesticated legumes, described as pulse-crops, are vital global inputs to human nutrition, particularly the various species, and varieties, of peas and beans. Populations of nitrogen-fixing bacteria live in root nodules of these crops. Pulses are therefore important sources of human food protein. Because they require low inputs of fertiliser, they are examples of 'sustainable production'. Fodder legumes are also a protein-rich food for farm livestock. In Britain, the breeding of white and red clovers makes an important contribution, when sown with grass, to create upland grazing pastures for sheep.

From this broad perspective there is great scope for developing work on legumes in order to support programmes of study in science which require illustrations of 'plants as organisms', and links with applied science.

Legumes, such as clovers and trefoils, as a distinct group, illustrate four levels of biodiversity. These were highlighted in the UK biodiversity action plan as an educational basis for answering the question 'What is biodiversity?'

These levels are:

- diversity between and within ecosystems;
- diversity between species;
- genetic variation within individual species;
- variation as a 'gene bank' for future developments in medicine and agriculture.

They have been incorporated into SCAN's curriculum guidelines for developing practical work to investigate 'biodiversity' (Fig 2). Each topic is a window into a programme of study in 'Science: Life processes and living things'. The knowledge net has been adapted for organising work on legumes, particularly clovers, in Fig 3

Fig 2 General knowledge net for studying biodiversity

Fig 3 Biodiversity knowledge net for studying legumes