Nitrogen-independent plants & seeds rich in energy and proteins 
Grain legumes are crop plants belonging to the legume family, which also includes forage legumes.
This botanical family is known as the Fabaceae, or alternatively the Leguminosae, and is characterised by:
- flowers that have five petals (papilionaceous flower with a butterfly form),
- a superior ovary that ripens to form a fruit, the specialised pod which contains seeds, and
- for nearly all of its members, the ability to use atmospheric nitrogen to produce their own protein compounds, as a result of the symbiosis with nitrogen-fixing bacteria within organs known as nodules developed on the plant roots.
Therefore, thanks to this third characteristic, unlike other cultivated plants, legume crops do not need nitrogen fertilisation for optimal growth in general.

Forage legumes are grown so that the whole crop can be fed to animals, either by grazing or the production of silage or hay, or sometimes for industrial purposes. The clovers (Trifolium spp.) and medics (Medicago spp.) and especially lucerne (also known as alfalfa), are examples of forage legumes.
Grain legumes are crop plants cultivated primarily for their seeds which are harvested at maturity and are rich in protein and energy. The mature dry seeds of grain legumes are usually called pulses in the trade and industry sectors. They are used either for animal feed or for human consumption. The term pulses excludes the ‘leguminous oilseeds’, such as soyabeans, that are used primarily for their high oil content.
More about terminology in the brief Lexicon (in different languages).

More than forty species and countless varieties of grain legumes are cultivated throughout the world, and a distinction is sometimes made between temperate (or cool season) and tropical (or warm season) types, although the species within these categories can vary.
Of the major grain legumes grown in Europe, peas (Pisum sativum), faba beans (Vicia faba) and lentils (Lens culinaris) belong to the tribe Fabeae (widely known as the Vicieae), soyabeans (Glycine max) and Phaseolus beans belong to the Phaseoleae, lupins (Lupinus spp.) belong to the Genisteae and chickpeas (Cicer arietinum) to the Cicereae.

Three-quarters of the world production of grain legumes (185 million tonnes) is soyabeans, grown primarily in the USA, Brazil, Argentina, Paraguay and Uraguay, for their fat content (20%) and the high-protein by-product soyabean meal destined for the animal feed industry. The world production of soyabeans has increased by 215% over the last 30 years compared with just 50% for other grain legumes.
The world production of grain legumes other than soyabeans amounts to 57 million tonnes.
The European Union with 25 member-states (EU25) has only 2% of world grain legume production, 0.5% of soya world production and 9% of other grain legumes.
(More in the pages 'Trends in production').

More about botany and phylogeny
There is confusion as to the correct name for the family, and whether leguminous plants should be treated as one family or three. Both names,  Fabaceae and Leguminosae, are acceptable following Articles 18.5 and 18.6 of the International Code of Botanical Nomenclature (ICBN) (Greuter et al. 2000). However, if the suffix ‘aceae’ is to be added in all cases to the stem of a legitimate name of an included genus, then Fabaceae is the only legitimate name for the family, derived from the genus Faba (now considered a generic synonym of Vicia). On the other hand, the family name Leguminosae has existed as an accepted alternative name for Fabaceae since the 1978 ICBN that permits the use of alternative names for eight large well-known and long-established families “sanctioned by long usage” (Lewis et al. 2005).

Although Fabaceae is the name used for the family by the Angiosperm Phylogeny Group (APG) and an increasing number of legume specialists, others consider its use to be ambiguous because of the difficulties that arise when this very large family (650 genera and over 18,000 species) is split into three subfamilies or sometimes, but less often, three separate families:
- Subfamily Caesalpinioideae or family Caesalpiniaceae
- Subfamily Minosoideae or family Mimosaceae
- Subfamily Faboideae (= Papilionoideae) or family Papilionaceae (= Fabaceae sensu stricto).
Thus Fabaceae may be used in two senses, a wide one (sensu lato) where it refers to legumes as a whole (three subfamilies) or a narrow one (sensu stricto) where it refers to the subfamily Papilionoideae (containing the genus Faba) of the family Papilionaceae.

The alternative family name Leguminosae can only be used in the wide sense with Caesalpinioideae, Minosoideae and Papilionoideae at the subfamily level. This is the taxonomic nomenclature adopted by Lewis et al. (2005).

The Papilionoideae is the largest of the three subfamilies of the Leguminosae and it displays the widest range of morphological diversity. The grain legumes belong to this subfamily, but there are different schools of thought regarding the positioning of the different grain legumes genera in the tribes of the Papilionoideae subfamily.

Sources
Greuter, W. et al. (Eds) (2000). The International Code of Botanical Nomenclature (Saint Louis Code). Köeltz, Konigstein, Germany.
Lewis, G., Schrirer, B., Mackinder, B. and Lock, M. (Eds) (2005). Legumes of the World. Royal Botanic Gardens, Kew, London, UK.
http://encyclopedia.thefreedictionary.com/Fabaceae
http://encyclopedia.thefreedictionary.com/Legumes
http://www.hort.purdue.edu/newcrop/proceedings1990/V1-154.html