legume [ LEG-yoom, li-GYOOM ] noun: a dry, dehiscent fruit derived from a single carpel, usually opening along two seams; plant belonging to the Fabaceae
Photo © Elaine Mills
In French, the word légumes refers to vegetables in general while in English legumes is commonly used to denote particular vegetables, namely beans, peas, and the like. However, in botany, legumes are not vegetables at all but the fruit of the Fabaceae (pea, bean, and legume family, originally called the Leguminosae).
The fruit is a dry, several seeded, often long, two-seamed pod that develops from a flower with a single-celled ovary. The pods are mostly dehiscent and when mature split along both seams exposing the seeds within. Two legumes, whose seams do not naturally split open, are peanuts and carobs. Follicles are sometimes referred to as pods and may be mistaken for legumes, but they dehisce only along one suture.
The Fabaceae are the third largest family among the angiosperms with 20,000 species. They include staple food crops, like beans and peas, with significant agricultural value as relatively inexpensive sources of protein and other nutrients, as well as forage crops for livestock, like alfalfa and clover, all of which have the ability to replenish soil that has been depleted of nitrogen and improve soil aggregation and microbe diversity and activity. They also include perennials like native Baptisia australis (blue wild indigo), Senna obtusifolia (sicklepod), and Thermopsis (false-lupines); deciduous trees such as natives Cercis canadensis (eastern redbud), Cladrastis kentukea (American yellowwood), and Robinia pseudoacacia (black locust) and invasive Albizia julibrissin (mimosa); and vines such as Lablab purpureus (hyacinth bean), invasive Pueraria montana (kudzu), and Wisteria (both native and invasive).
Left to right: Native Baptisia australis, Senna obtusifolia, Thermopsis villosa, natives Cercis canadensis and Cladrastis kentukea, invasive Albizia julibrissin, Dolichos lablab.
Since ancient times, legumes have been cultivated across the globe for human consumption. They are dependable and easy to grow, with low water use and the capacity to improve rather than deplete the soil. They are a food rich in protein, fiber, essential amino acids, vitamins, and minerals and mostly low in fat. The dried seeds, known as pulses, have a long shelf life during which they maintain their nutritional value. Regular consumption of legumes has been linked to the prevention of several chronic diseases. Crop legumes are usually divided into several categories:
- Pod beans are harvested when the pods are young and tender and the entire fruit is eaten fresh as a vegetable. These include the common bean—green bean, French bean, snap bean, string bean, yellow wax bean—(Phaseolus vulgaris, indigenous to the Americas) along with snow pea and sugar snap pea (Pisum sativum var. macrocarpon, native to the Mediterranean region and Near East), fava or broad bean (Vicia faba, native to north Africa and southwest Asia), and red noodle bean (Vignaunguiculata ssp. sesquipedalis, originating in southeast Asia).
Left to right: Green bean legumes, Dragon Tongue (purple-streaked white) and Roma II (green) legumes, red noodle bean legumes, sugar snap pea legumes.
- Fresh-shelled beans are harvested when the pods are plump with full-size, tender seeds. The seeds are removed from the pod, which is discarded, and prepared and eaten while soft. These include the black bean, cannellini bean, and cranberry or borlotti bean varieties of Phaseolus vulgaris, lima or butter bean (Phaseolus lunatus from Central and South America), and garbanzo bean or chickpea (Cicer arietinum, originating in southeastern Turkey), all of which are also harvested dried. The pods of edible soybean (Glycine max, native to East Asia), which the Japanese call edamame, are cooked and served intact, but only the seeds are consumed by biting down on the pod to pop the seeds into the mouth, after which the pod is discarded.
- Dried beans are harvested when the seeds rattle in the mature, dried-out pods. The pulses are also shelled and the pods discarded. They are stored dry or canned. Pulses include the kidney bean, navy bean, pinto bean, and white bean varieties of Phaseolus vulgaris as well as lentil (Lens culinaris, native to France, Spain, and parts of the Middle East), adzuki bean (Vigna angularis, indigenous to East Asia), mung bean (Vigna radiata, originating in the Indian subcontinent) and cowpea or black-eyed pea (Vigna unguiculata, indigenous to sub-Saharan Africa).
- Oilseed legumes such as soy bean and peanut (Arachis hypogaea, originating in eastern South America) are relatively high in protein and fiber like other legumes but both are considerably higher in fat content and peanuts are much higher in calories.
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Note: Some legumes and seeds contain compounds that can release toxins when consumed raw or if they are not properly prepared—thoroughly soaked and/or cooked at a certain temperature for a specified amount of time.
References
COWPEA. PEA. USDA, NRCS. 2023. The PLANTS Database (http://plants.usda.gov, 02/27/2023). National Plant Data Team, Greensboro, NC USA.
Crawford E. et al. 2019. All About Beans Nutrition, Health Benefits, Preparation and Use in Menus (FN1643). Ag Home. Extension. North Dakota State University.
FAO. 2016. Pulses: nutritious seeds for a sustainable future. Rome. ISBN: 978-92-5-109172-2.
Glycine max. Phaseolus vulgaris,. Pisum sativum. Missouri Botanical Garden Plant Finder.
Keshavarz R, Didinger C, Duncan A, Thompson H. 2020. Pulse Crops and their Key Role as Staple Foods in Healthful Eating Patterns – 0.313. Colorado State University Extension.
The Editors of Encyclopaedia Britannica. Updated February 18, 2023. legume fruit of Fabaceae plants. Encyclopaedia Britannica.
Zapp M. Updated July 27, 2022. Dried Beans Versus Fresh Shelled Beans. Penn State Extension.