The legume family (Leguminosae)

The Leguminosae (alternative name Fabaceae) is the third largest flowering plant family, containing 19,325 species, and accounts for over 8% of the world’s flowering plants.

The legume (or bean) family, which includes lentils, peas, beans, peanuts and soya, is hugely important as a source of food due to its high protein content. It is second only to grasses (cereals) in agricultural importance, and many species are also used for forage, hay, silage and green manure.

Typical pea flowers of Styphnolobium japonicum (pagoda tree). (Image: Brian Schrire)

About legume species

Species of legume are found throughout the world in a wide variety of habitats that include arid environments and tropical rainforest, and range in size from small herbs to huge tropical forest trees.

The majority of species have leaves subdivided into smaller leaflets and flowers with five petals, five sepals, ten stamens and one ovary, but there exists many exceptions to this floral groundplan. The fruit of many species is a pod or legume that opens its two halves to disperse the seeds, but again there are many exceptions.

Currently the legume family is divided into three subfamilies, but molecular research has conclusively shown that one of these will need to be divided further into more subfamilies in the future.

Legumes and fungi

Many legumes are able to fix atmospheric nitrogen through an association with root bacteria or have a close association with species of fungi, both strategies allowing them to colonise and grow in even the poorest soils, whilst also helping to stabilise and improve them. For this reason their economic importance is likely to grow as humans put more and more pressure on marginal lands.

Find out more about plant-fungal relationships

Rough sawn brown salwood (Acacia mangium) billets ready for further processing in Johor State, Malaysia. Image: Stephen Midgley, 2007

A source of hardwoods

Legumes are also a source of some of the best hardwoods (e.g. the so-called rosewoods from Dalbergia species and the bloodwoods from Pterocarpus species). Professional violin bows are today still manufactured from the Brazilian legume tree Caesalpinia echinata. In addition, a significant number of legumes are important sources of dyes (e.g. the blue dye indigo from a number of Indigofera species), gums (such as gum arabic from Acacia), oils (from, for example, Copaifera species), medicines and fuel.

Kew's legume work

The Leguminosae are an important focus of research at Kew. The Kew legume team undertakes research across many disciplines, and contributes to a network of global expertise on the subject. The team’s aim is to fill in the gaps in our knowledge of the group through research into the classification, evolution and diversity of the family, using this to aid sustainable use and conservation projects especially in threatened environments. It explores the many and varied uses of legumes and also looks after the various legume collections at Kew which are so important to current and future plant biologists.