Azuki, sometimes spelled adzuki and called red bean (Vigna angularis), is the name of the second most important legume in Japan after soybeans. Its annual production in China is estimated at 800,000 metric tons.
About 100 species of the pantropical Vigna have been reported, most in Africa and Asia. Nine of them have been domesticated, two in Africa and seven in Asia. Azuki is closely related to the cowpea or yardlong bean (V. unguiculata), mungbean (V. radiata), and several species in the genus Phaseolus.
Wild Form
The domestic azuki is presumed by researchers to have been developed from the wild bean Yabutsuru-azuki (V. angularis var nipponensis), and that plant is currently found throughout Japan, the Korean peninsula, China, Nepal and Bhutan. Forms of azuki that are intermediate between domesticated and wild are primarily found in Korea and Japan.
The differences between domestic and wild azuki include morphological and physiological traits, with domestic forms showing fewer but larger seeds (generally eight times that of the wild), fewer but longer pods, and a broader range of habitat choices. The domestic version does not twine as much as the wild one does, and seed dispersal and dormancy are reduced in the domesticated azuki.
Seed and coat color variation is present in azuki cultivars. Unlike the wild beans, which have black and mottled patterns on a grey or green seed coats, domesticated forms have typically red or white seed coats. Wild seeds vary in color between yellow brown, grey, yellow green and brown mottles on light brown skin; cultivated ones typically are plain white, black or black mottled on red or variegated red skins.
Domestication History
Scholars agree that azuki was domesticated in East Asia, but there is no conclusive consensus concerning exactly where that might have occurred: strong candidates include Korea, Japan and China. Some of the evidence cited in the literature includes the fact that Azuki has existed as a crop complex for quite a while in Japan; and in historic documents dated to the Chinese Eastern Zhou dynasty (1046-256 BC), azuki is said to have been domesticated later than other crops.
A Himalyan form (V. nepalensis) appears to be the most closely related wild version to cultivated azuki beans. Carbonized azuki bean seeds have been found in archaeological sites in Japan dated about 4,000 years ago, predating those found in China and Korea. The oldest well-preserved specimens in Japan are in Jomon sites dated 8,000 cal BP, and the frequency of azuki reports increases through the Late Jomon.
Why Don't We Know?
One hindrance to determining the original location of domestication is the high percentages of introgression between the wild and cultivated forms: they can interbreed, resulting in intermixed genetic structures. The ready expansion of wild azuki into human habitats may have assisted domestication, in that some morphological and physical changes in the beans may have been created as a result of moving near organic-rich neighborhoods. That too muddies the specific wild/domestic interpretation.
In addition, identifying the secure domestication location is difficult because azuki is not easily differentiated from the mung bean: and in general seed colors are not distinguishable in archaeological specimens.
The safe bet, and it's probably what we'll have to live with for a while, is that azuki was domesticated someplace in east Asia, by no later than ca 5,000 cal BP.
Important Sites for Azuki
- Shizitan Locality 9 (China), Late Paleolithic, 13,800-8500 cal BP
- Torihama (Japan), Early Jomon, ca 8000 cal BP
- Pyeonggeodong (Korea), Middle Chilmun), 4960-4650 cal BP
- Shimoyakabe (Japan), Middle Jomon, 4890-4850 cal BP (soybean or azuki)
- Lianchengzhen (China), Late Longshan, 4060–3840 cal BP
- Dunggasi (China), Shang, 3600-3300 cal BP
- Daundong (Korea), Middle Mumun, 2900-2500 cal BP
Sources
This glossary entry is a part of the About.com guide to Plant Domestication, and the Dictionary of Archaeology.
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