Leguminosae
Introduction
The Leguminosae (Fabaceae or bean family) is the third largest flowering plant family with 19,325 species in 728 genera and constitutes nearly one twelfth of the world’s flowering plants.
The legume family is of great significance because so many species are used throughout the world as sources of food and medicine. It is second only to grasses in economic importance and supplies foods, fodder and a wide range of products to many millions of people around the world, although fewer than 50 legume species provide 90% of the world's current legume requirements. Legumes provide some of the finest hardwoods and are valued for dyes, gums, oils, medicines and as fuels. Chemical defences are critical in legumes and have evolved, in part, to protect their protein-rich seeds from pests. Enormous potential exists to utilise more species but, without baseline taxonomic work leading ultimately to a detailed understanding of species circumscription and variation, this potential will not be met. Centres of legume diversity include Brazil, Cuba, Mexico, New Caledonia, and South and West Africa. All of these areas are threatened with habitat destruction, which is particularly significant in the drylands and wet tropics. There is an urgent need to document and study in detail the legumes of these areas. The IUCN World List of Threatened Tree Species (1998) includes 697 legume taxa (in 158 genera), some of which are very poorly known and might be close to extinction in the wild. The list is far from complete. The nutritive value of legumes is largely due to their special ability to accumulate nitrogen. Rhizobia in root nodules and fungal associations assist leguminous plants to scavenge essential elements from even the poorest soils. This versatility of legumes enhances their economic importance, which is likely to increase as human pressures demand more effective use of marginal land. The ability of legumes to stabilise and improve soils, while also offering natural products of potential value to the grower, was first recognised in arid regions where many systems of agro-forestry now use legumes as a major component. Legumes have thus become a natural major focus of Kew’s seed bank collecting programme within the drylands and thus constitute a large component of Kew’s ex situ conservation work.
Leguminosae and close relatives in the Fabales clade (Polygalaceae, Surianaceae and Quillajaceae) are an important focus of research at Kew. The Kew legume team undertakes multidisciplinary research in collaboration with a global legume network. The team is centred around the Legume Section in the Herbarium and is strengthened by staff with legume interests from the Jodrell Laboratory (Molecular Systematics, Sustainable Uses, and Micromorphology sections), HPE (through sizeable living collections) and the Seed Conservation Department (ex situ conservation of legume seed). A key strength of the team is its unsurpassed knowledge of legume genera across their global range, permitting regional, monographic and global syntheses of the family. The rapid advance in legume systematics in the past ten years, based on wide-ranging analyses of multiple data-sets including sequence data, has resulted in the documentation of many novel patterns of relationship at the genus level and above, and these, in turn, provide the backbone for a new legume classification. The multidisciplinary approach of Kew`s legume science is now addressing gaps in the big datasets, as well as reanalysing old data in light of the new phylogenies and generating new data in pollen, wood and chemical research to test existing hypotheses and create new ones. As of January 2006, the seed bank at Wakehurst Place included 4,446 legume accessions representing 1,740 species in 280 genera. The intraspecific variation held in this collection is important for future habitat restoration and other conservation strategies. What is needed for the legume team to grow strategically is more space for collections, an increase in the targeted collection of research material, more combined data analyses to develop robust hypotheses of relationship, and an increase in top quality PhD students and post-doctoral research fellows.
The overall objective of the team is to increase knowledge of legume diversity, evolution, classification, conservation and use through high quality research, and to disseminate these results widely. The team also cares for the many different legume collections across the institution and curates these to the highest standard so that future generations of plant biologists have access to the best research resources. Legume specimens are also being electronically databased and imaged as part of long-term data-sharing and capacity building programmes with partner countries. Web-based projects are being developed to capture at the generic level legume information recently published in Legumes of the World, and at the species level through joint work using the International Legume Database and Information Service (ILDIS).
In terms of existing expertise, Kew has a broad generic view across the family, regional expertise in major tropical areas, and taxonomic speciality at tribal and subtribal level in selected groups. There has also been extensive multidisciplinary work in the comparative biology of legumes based on wood anatomy, pollen morphology, molecular systematics, comparative phytochemistry and uses. The combined data from these disciplines have highlighted the need for a radical restructuring of higher level legume classification, a project in which the Kew legume team is actively involved.
The expertise, wide range of legume taxa, and the extensive research facilities at Kew have been the impetus for targeting problems identified through the international legume conferences, including, for example, the circumscription and phylogeny of basally branching lineages in Caesalpinioideae and Mimosoideae, and the disputed position of Swartzieae between Caesalpinioideae and Papilionoideae. Revisions and monographs have been undertaken of large, economically important, multi-use genera in the tropics, including Inga, Acacia, Caesalpinia, Crotalaria, and Indigofera, with the aim of producing illustrated, user-friendly identification manuals. Each project has been developed around a collaborative network of partners for maximum effectiveness. In 2005 Kew published Legumes of the World, an output developed from Kew`s long-standing expertise in legume systematics, its globally-based collections and international network.
The legume team provides a specialist naming service and is active in the production of checklists, Floras and monographs that aim to provide the fundamental identification and classification on which so many users depend. All of these resources are directed towards improved conservation and plant-use programmes, particularly in areas rich in legumes. Documenting and exploring the many and varied uses of legumes is a major component of the team's work.
Information is synthesised partly through the ILDIS, which provides the framework for nomenclatural consensus. As a major contributor to the ILDIS, Kew is helping to build a comprehensive species-level database of the family across its global range and has published two regional checklists since 2003. The database currently holds about 36,000 names covering c. 19,000 taxa and is the leading example of its type. This links to Kew`s broader global checklist development programme and its commitment to meeting target 1 of the Global Strategy for Plant Conservation.
The legumes are generally understudied in the drylands of South America and there is still need for more work in the drylands of Africa. There is also a need for work on phylogenetically basally branching lineages to understand the diversification of the Leguminosae in more detail, and on the large genera (the family has 41 genera with more than 100 species each) which account for the majority of the species diversity in the family. These will continue to be key elements of the future strategy of legume research at Kew.