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Leguminosae

The Leguminosae (Fabaceae or bean family) is the third largest flowering plant family with 19,400 species in 740 genera and constitutes nearly one twelfth of the world's flowering plants. Leguminosae and close relatives in the Fabales clade (Polygalaceae, Surianaceae and Quillajaceae) are an important focus of research at Kew.

Research at Kew

Legumes, in particular, have been a focus family at Kew since the work of Bentham in the mid 19th century. More recently, participation in a growing number of multi-disciplinary projects, both within and outside Kew, as well as in five International Legume Conferences, has shaped the present thrust of legume research at Kew and to a large extent internationally. The conferences alone have generated 13 volumes (11 published by Kew) in the Advances in Legume Systematics, Advances in Legume Science, and Advances in Legume Biology series and Kew staff, across several departments, have made major contributions to these. 

Research is multi-disciplinary and includes studies in phytochemistry, wood anatomy, palynology, plant-animal interactions, sustainable plant use, reproductive biology, ontogeny, molecular systematics, seed germination and storage, and taxonomy. The team is a major contributor in an international network, with a broad focus on higher level systematics, effective use of modern techniques and increasing use of electronic media for identification, inventory and GIS.

The staff 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 Acacia, Berlinia, Caesalpinia, Crotalaria, Indigofera, and Inga, 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.

Over recent years Kew’s regional focus for legumes has been in Eastern and Southern Africa, Cameroon, Gabon, Madagascar, Mexico, Brazil, Bolivia, Peru and Ecuador – the breadth of this focus is not matched at any other institute. Fieldwork has been geared to collecting critical taxa by region and providing a wide range of plant materials to facilitate collaboration. The material is cross-referenced to authentically named herbarium vouchers.

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.

The overall objective of the legume team at Kew 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.

Economic importance of legumes

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.

Legume collections

Since 2006, between 3,000 and 4,000 new herbarium specimens have been accessioned each year, and on average the legume collection receives two international visitors per week, peaking to five or more during university vacations or conferences. It is a policy of the legume section to ensure that users have access to the most recently accessioned material and to collections carefully curated according to the most up-to-date revisions and monographs. Floristic work has provided the nucleus for more detailed monographic work and has been an essential first step towards an inventory of the legumes in under-explored areas.

The legume collection in Kew's Herbarium is one of the most comprehensive in the world (with about 750,000 specimens, including c. 30,000 types) and uniquely contains global representation of nearly all 740 genera currently recognised, thus making it ideally suited for targeted monographic and floristic work and multi-disciplinary science. The whole legume collection has been moved from the old part of the Herbarium to the new Wing E building, a task that took nearly a year to complete. The 740 legume genera have been rearranged by a new classification based largely on Legumes of the World published in 2005, and this is a radical update of the previous Bentham and Hooker (1865) arrangement.

The Herbarium collections are cross-referenced to extensive ancillary collections such as fruits (6,000+ samples), material preserved in spirit (c. 2,000), illustrations (6,000 many originals), and over 14,000 photographic images. Major genetic resources are the seed collections, live plants (c. 1,300 plant accessions covering over 800+ taxa), and the DNA Bank (2007 legume accessions).

The Herbarium houses c. 5,000 comparative seed collections (including those in the Krukoff collection), and 2,634 fruit and seed samples representing 150 genera are held in the Economic Botany Collections (EBC). In addition, the EBC holds a total of 9,932 specimens and artefacts of legume origin (4,749 of which are wood samples) in their collections.

Currently on the micromorphology slide database there are 2,424 legume slides (including many additions since 2005, especially for the genera Acacia and Dalbergia). There are c. 190 legume chromosome collections covering c. 110 species, 2,854 mass spectrometric analyses (LC-MS and GC-MS) of extracts of legumes archived electronically, and over 3,085 pollen slides covering 2,516 species (for the whole Fabales clade 3,196 slides representing 2,599 species).

As of October 2011, the seed bank at Wakehurst included 8,576 legume accessions representing 3,430 species in c 300 genera. The intraspecific variation held in this collection is important for future habitat restoration and other conservation strategies.

Databases

Legume researchers at Kew have access to the plant micromorphology bibliographic database, the economic botany bibliographic database, extensive bibliographic and pictorial resources in the library and a comprehensive reprint collection. Kew compiles, edits and globally distributes the annual legume systematics newsletter Bean Bag. On average, two to three, international visitors consult the various legume collections every week. A significant number of these are long-term visitors (two months or longer).

Legume specimens are 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.

Future work

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.

What is needed for the legume team to grow strategically is 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.