Kuwai
From Wikipedia, the free encyclopedia
Kuwai (Japanese: クワイ) is a Japanese plant whose underground stem (rhizome) is edible. It is a cultivar of Sagittaria trifolia. It has different common names in different regions of Japan.[1] The underground stems of this neighboring species are also eaten in China.
Kuwai and Chinese cígū (慈姑) are different cultivars, but both are treated as kuwai in Japan and cígū in China. The etymology of the Japanese name kuwai is uncertain.[2]
Kuwai is a cultivar of Sagittaria trifolia. Its scientific name is Sagittaria trifolia L. 'Caerulea.'[3] However, it is sometimes treated the same as another cultivar or as the same as Sagittaria trifolia. On the contrary, some scholars have assumed it to be Sagittaria sagittifolia without acknowledging Sagittaria trifolia.[4]
The cultivar Sagittaria trifolia was created in China.[1] For this reason, the origin of kuwai is considered to be China.[5] It is cultivated as a vegetable only in China and Japan.[5] In Japan, it has been actively cultivated since the Edo period.[6]
Chinese kuwai is white, and its underground stem is larger than the Japanese one. This underground stem is also edible in China. It is cultivated only in Japan, but it is called shiro(white)-kuwai to distinguish it from Japanese kuwai. In contrast, Japanese kuwai is sometimes called ao kuwai to distinguish it from Chinese kuwai. In Japan, the scientific name of the white kuwai is often given as Sagittaria trifolia L. 'Sinensis', while the same species is known as Sagittaria sagittifolia subsp. leucopetala in China.[4]
In Japan, three varieties of kuwai are grown: the blue-violet ao kuwai, the pale blue shiro kuwai, and the small Suita kuwai.[7] All are grown in paddy fields.
- Ao kuwai
- This is the most common variety grown in Japan. Its grass is relatively short, and its leaves are medium-sized and green. Its tuber is oblong, and its outer skin is blue. Among the ao kuwai strains, the one with a flat bottom of the tuber is called Shinden kuwai, and the slightly waist-high, round-bellied strain is called Kyo kuwai.[8] The underground stem weighs 6 g.[9]
- Shiro kuwai
- This variety is widely grown in China and is rarely seen in Japan. It is a tall plant with large, light green leaves. [8] The tuber is white in color, round and spherical, and its flesh is tougher than that of ao kuwai and has a crunchy texture.[10] Its taste is light and bitter.[8][7] It is used as an ingredient in Chinese cuisine.[8] The weight of the underground stem is 28g.[9]
- Suita kuwai
- The closest wild variety of kuwai to Omodaka, with smaller tubers but denser flesh and less bitterness, and said to have a good taste.[8][7] It is also said to be a strain of Omodaka[8] The botanist Tomitaro Makino gave it the scientific name as a variety of omodaka, which was cultivated in Japan apart from the introduced lineage.[11] The weight of the underground stem is 4 g.[9]
Distribution
As mentioned above, the distribution of kuwai varies greatly depending on how it is classified. If we consider it Sagittaria sagittifolia, it is widely distributed in Asia, Europe, the Americas, and other regions of the world, from temperate to tropical across the globe. The wild species Sagittaria trifolia is believed to be native to Southeast Asia. The cultivated variety kuwai was created in China.[1] For this reason, the origin of kuwai is China.[5] The areas where it is cultivated as a vegetable are limited to China and Japan. [5] In Japan, it has been actively cultivated since the Edo period. [6]
Plant life
Plant forms
Ao kuwai, a typical Japanese kuwai, is a monocotyledonous perennial aquatic plant, growing to about 110 - 125 centimeters (cm) in height.[5] The leaves are 30 cm long, arrowhead-shaped without notches, and the leaf blade has a spongy interior.[5] Stolon arise from each node of the stem and grow up to 60 – 80 cm long.[5] Nodes are also found on the creeping stem, from which two or three secondary creeping stems arise.[12] Tubers are attached to the tips of the rhizome, which are larger than those of the original omodaka species. The tuber is bluish with horizontal nodules and is surrounded by thin scales with a 5 – 6 cm long apical bud at the tip. The flowers are dioecious. It produces conical inflorescences with white-petaled flowers. Fruiting is almost non-existent after flowering.[12]
Growth
Kuwai is cultivated in paddy fields. Germination of kuwai occurs around early July, when planting takes place, at a germination temperature of 13 °C to 15 °C or higher.[12] The growth of kuwai can be divided into two phases: the vegetative growth phase (July–August), from germination to leaf number increase, and the reproductive growth phase (late August to mid-November), from creeping stem development to tuber enlargement.[13] The optimum temperature for growth during the vegetative growth phase is 20 °C to 30 °C, but the rate of increase in leaf number is temperature-dependent and is accelerated by high temperature conditions.[13] Creeping during the vegetative growth period occurs after 14 to 15 true leaves have developed, followed by the development of one creeping stem for every leaf blade.[13] After the creeping stems have elongated, they form tubers encased in two bracts, which begin to enlarge when daylight hours are shortened and the plant is exposed to low temperatures of around 15 °C.[13] Although the stolons die when exposed to frost, tuber enlargement takes place below the water surface until late fall.[13]
