Azuki bean (Vigna angularis)

Azuki bean (Vigna angularis) is a plant species in the Fabaceae family. It is an annual herb—bushy and erect, though sometimes trailing or creeping—that can root at the stem nodes and reach heights or lengths of up to 90 cm. It possesses a taproot 40–50 cm in length.

The leaves are alternate and trifoliolate. The stipules are small and peltate, often three-branched with a basal appendage, while the stipels are lanceolate. The leaflets range from lanceolate to ovate, measuring 5–10 cm in length and 5–8 cm in width; they are acuminate (tapering to a point) and may be entire (unlobed) or three-lobed.

The inflorescence is an axillary pseudo-raceme containing 2–20 flowers. The pedicels (flower stalks) are long on the lower nodes and become very short toward the upper nodes. The flowers are bisexual and papilionaceous (pea-like). Each flower has a short pedicel with an extrafloral nectary at its base. The bracteoles are longer than the calyx. The calyx is bell-shaped with short teeth.

The corolla is 15–18 mm long and bright yellow; it consists of a rounded standard (banner petal), oblong wings, and a keel that curves to the right, featuring a horn-like spur on the left side. There are 10 stamens, with 9 fused together and 1 remaining free. The ovary is superior and covered in short hairs; the style curves sharply near the top and is hairy on one side toward the apex, ending in a lateral, disc-shaped stigma.

The fruit is a cylindrical pod, 5–13 cm long and 0.5 cm wide. The pods are pendulous (hanging downward), slightly constricted between the seeds, and appear pale yellow, blackish, or brown; each contains 2–14 seeds. The seeds are cylindrical with rounded ends, somewhat flattened, 5–7.5 mm long, and 4–5.5 mm wide. They have a smooth surface and can be wine-red, cream, yellowish-cream, black, or mottled. The weight of 1,000 seeds ranges from 50 to 200 g. The seeds germinate underground, producing a single pair of opposite, heart-shaped primary leaves.

V. angularis grows at temperatures between 15–30°C, with an average annual rainfall of 500–1,750 mm and a soil pH of 5–7.5. Seeds can remain viable for up to 5 years if stored at a moisture content of approximately 13% and a relative humidity of 15%. Germination requires a soil temperature of 6–10°C, with an optimal range of 30–34°C. Seedling emergence takes 7–20 days. Growth is slow. The flowering phase lasts for 30–40 days and may occur up to three times. The total growth duration for this species is 60–190 days. Nitrogen fixation rates can reach 100 kg N/ha. The roots form nodules through a symbiotic relationship with Bradyrhizobium bacteria.

The seeds have a sweet flavor with a nutty undertone. Once dried, the mature seeds can be consumed whole after being cooked. They are also processed into flour for use in soups, cakes, various snacks, and ice cream, and are even utilized in the production of shampoos and face creams. Immature seeds and sprouts can be eaten as vegetables. The seeds can serve as a coffee substitute or be processed into confections. The plant is also cultivated for livestock fodder, green manure, and soil conservation.

The seeds exhibit a hypocholesterolemic effect. Hot-water extracts show hypoglycemic and antitumor properties, while aqueous extracts from the seed coat demonstrate hepatoprotective activity. The seeds are used to address kidney disorders, constipation, abscesses, certain types of tumors, the threat of miscarriage, retained placenta, breast milk production, blood circulation, and urinary issues. The leaves are used to alleviate fevers, and the sprouts are used to prevent miscarriages caused by injury.

Raw seeds (per 100 g) contain 13.4 g of water, 1377 kJ (329 kcal) of energy, 19.9 g of protein, 0.5 g of fat, 62.9 g of carbohydrates, 12.7 g of dietary fiber, 66 mg of calcium (Ca), 127 mg of magnesium (Mg), 381 mg of phosphorus (P), 5.0 mg of iron (Fe), 5.0 mg of zinc (Zn), 17 IU of vitamin A, 0.46 mg of thiamin, 0.22 mg of riboflavin, 2.6 mg of niacin, 0.35 mg of vitamin B6, 622 μg of folate, and 0 mg of ascorbic acid. Essential amino acids (per 100 g) include tryptophan 191 mg, lysine 1497 mg, methionine 210 mg, phenylalanine 1052 mg, threonine 674 mg, valine 1023 mg, leucine 1668 mg, and isoleucine 791 mg. The primary fatty acids (per 100 g) include linoleic acid 113 mg and oleic acid 50 mg.

TAXON

Kingdom: Plantae
Phylum: Tracheophyta
Subphylum: Angiospermae
Class: Magnoliopsida
Order: Fabales
Family: Fabaceae
Subfamily: Faboideae
Tribe: Phaseoleae
Subtribe: Phaseolinae
Genus: Vigna Savi in Nuovo Giorn. Lett., ser. 3, 8: 113 (1824)
Species: Vigna angularis (Willd.) Ohwi & H.Ohashi in J. Jap. Bot. 44: 29 (1969)

HOMOTYPIC SYNONYMS

Azukia angularis (Willd.) Ohwi in Bull. Natl. Sci. Mus. Tokyo 33: 77 (1953)
Dolichos angularis Willd. in Sp. Pl., ed. 4. 3: 1051 (1802)
Phaseolus angularis (Willd.) W.Wight in Bull. Bur. Pl. Industr. U.S.D.A. 137: 17 (1909)

HETEROTYPIC SYNONYMS

Azukia angularis var. nipponensis (Ohwi) Ohwi in Fl. Jap. (Tokyo): 691 (1953)
Dolichos angulatus Willd. in Enum. Pl. Hort. Berol., Suppl.: 51 (1814)
Phaseolus atsuki Siebold in Verh. Batav. Genootsch. Kunsten 12: 57 (1830)
Phaseolus nipponensis Ohwi in J. Jap. Bot. 13: 435 (1937)
Vigna angularis var. nipponensis (Ohwi) Ohwi & H.Ohashi in J. Jap. Bot. 44: 30 (1969)

PUBLICATIONS

Acevedo-Rodríguez, P. & Strong, M.T. (2012). Catalogue of seed plants of the West Indies. Smithsonian Contributions to Botany 98: 1-1192.

Balslev, H. & Chantaranothai, P. (2023). Flora of Thailand 4(3.3.): 489-715. The Forest Herbarium, Royal Forest Department.

Chang, C.S., Kim, H. & Chang, K.S. (2014). Provisional checklist of vascular plants for the Korea peninsula flora (KPF): 1-660. DESIGNPOST.

Coi, B.H. in Lee, Yong No (2024). Flora of Korea 5a-3: 1-97. Kyo-Hak Publ. Co., Ltd.

Kumar, S. & Sane, P.V. (2003). Legumes of South Asia. A Checklist: 1-536. Royal Botanic Gardens, Kew.

Lee, W.T. (1996). Lineamenta Florae Koreae: 1-1688. Soul T'ukpyolsi: Ak'ademi Sojok.

Lock, J.M. & Heald, J. (1994). Legumes of Indo-China a check-list: 1-164. Royal Botanic Gardens, Kew.

Lock, J.M. (1989). Legumes of Africa a check-List: 1-619. Royal Botanic Gardens, Kew.

Meena, S.L. (2012). A checklist of the vascular plants of Banaskantha district, Gujarat, India. Nelumbo 54: 39-91.

Nelson Sutherland, C.H. (2008). Catálogo de las plantes vasculares de Honduras. Espermatofitas: 1-1576. SERNA/Guaymuras, Tegucigalpa, Honduras.

Villaseñor, J.L. (2016). Checklist of the native vascular plants of Mexico. Revista Mexicana de Biodiversidad 87: 559-902.

Wu, Z. & Raven, P.H. (eds.) (2010). Flora of China 10: 1-642. Science Press (Beijing) & Missouri Botanical Garden Press (St. Louis).

Yakovlev, G.P., Sytin, A.K. & Roskov, Y.R. (1996). Legumes of Northern Eurasia. A checklist: 1-724. Royal Botanic Gardens, Kew.

Zhao, Y.Z., Zhao, L.Q. & Rui, C. (eds.) (2019). Flora Intramongolica, edition 3, 3: 1-513. Typis Intramongolicae popularis, Huhhot.

Zhu, X.Y., Zhang, R.P. & He, Y.L. (eds.) (2021). An inventory of legume species diversity of Myanmar: 1-297. China Minzu university press.

VERNACULAR NAME

Bunun: Bainukalitang
Chinese (simplified): 赤豆 - 红豆 - 红小豆
Chinese (traditional): 野紅豆 - 紅豆
Czech: Vigna hranatá
Dutch: Adukiboon
English: Azuki bean, Adzuki bean, Red bean, Red azuki bean, Red mung bean
Finnish: Adsukipapu
French: Haricot adzuki
Indonesia: Kacang azuki, Kacang merah kecil, Kacang tolo merah
Japanese: アズキ
Java: Kacang asuki
Korean: 팥
Polish: Fasola azuki
Portuguese: Feijão-azuqui e afins
Russian: Вигна угловатая
Slovak: Vigna hranatá

Aryo Bandoro
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