Oryza sativa (rice)

Oryza sativa is cultivated in Europe, Africa, tropical and temperate Asia, Australia, and North and South America.

Domestication of rice

The history of rice domestication is not fully understood. Its wild ancestor, Oryza rufipogon, grows throughout south and southeast Asia, and finds of rice at early sites in the region may derive from harvesting of wild grain, rather than cultivation. The earliest records of domesticated rice are probably those from the Lower Yangtze river valley of southern China, dating from about 6000 BC. Archaeological and historical evidence suggests that rice spread slower than most crops, in part owing to its specialised need for abundant water. For example, rice did not become an important crop in North America until the late 17th century.

Fruiting head of Oryza sativa (Image: RBG Kew)

The rice plant is a grass which can grow to over 1 m tall, or to 5 m long in deep water. The stem is upright and composed of a series of joint-like nodes, with a leaf growing from each node. The seeds (or grain) grow on branch-like spikes which arch over. The grain is the most economically important part of the rice plant, and its endosperm is the final product consumed.

There are many cultivar groups of Oryza sativa of which the two most important are O. sativa ‘Indica’ and O. sativa ‘Japonica’. O. sativa ‘Indica’ produces long-grain rice and is grown in tropical areas such as southeast Asia and the Philippines, whilst the short-grained O.sativa ‘Japonica’ is cultivated in temperate areas including Japan and northern China. Another species, O. glaberrima, is cultivated on a much smaller scale in Africa. ‘Wild rice’ is produced from an entirely different species of grass, Zizania palustris, and is harvested from wild plants in North America.

Harvesting rice (Image: RBG Kew)

After being harvested, rice is de-husked to remove the inedible hull. The resulting grains are usually eaten as white, polished rice from which the bran has been removed. Whole "brown" rice is mainly popular as a "health food" in western countries. Rice is most often consumed as whole grains, boiled or steamed in water. Rice flour lacks gluten and so is usually consumed as noodles, as the absence of gluten results in poor quality bread. Rice cultivars with starch that is low in amylose are waxy or glutinous, and are used industrially as a thickening agent for sauces and puddings, and in eastern Asia for snack foods, such as rice crackers and cakes.

The main rice-products used as medicines are made from brown rice and rice oil from rice bran. Some of the traditional medicinal uses of rice are supported by scientific studies. Rice can be used to treat skin conditions. The rice is boiled, drained, allowed to cool and then mashed. The rice is made into a paste or moulded into balls and these can be applied to boils, sores, swellings and skin blemishes. Other herbs are sometimes added to the rice balls to increase their medicinal effects. Sticky glutinous rice is often taken to treat stomach upsets, heart-burn and indigestion. Extracts from brown rice have been used to treat breast and stomach cancer and warts. They have also been used to treat indigestion, nausea and diarrhoea.

Laboratory studies have shown that rice products may have anti-cancer properties and the potential to treat other conditions such as diabetes, kidney stones and heart disease.

The medicinal properties of rice vary depending on the types used. Many of the beneficial compounds present in brown rice are absent from highly-refined white rice. Rice bran can contain up to about 25% fibre, which is known to assist the absorption of fats in the gut. It also decreases levels of cholesterol in the blood, aids digestion and can be used as a mild laxative. The oil from rice bran contains vitamin E and minerals. The vitamin E group of compounds in rice have antioxidant properties, and these compounds could explain some of the traditional medicinal uses of rice, particularly to treat cancer.

Kew's Millennium Seed Bank partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

Description of seeds: Average 1,000 seed weight = 27.5 g.
Number of seed collections stored in the Millennium Seed Bank: Four.
Seed storage behaviour: Orthodox (the seeds of this plant survive drying without significant reduction in their viability, and are therefore amenable to long-term frozen storage such as at the MSB)
Germination testing: 100% germination (germination medium = 1% agar; germination conditions = 26°C, 12/12).
Composition values: Oil content = 2.2-17.5%.

Kew's 'Difficult' Seeds Project - find out more about storing and germinating the seeds of Oryza sativa

You can see Oryza sativa growing in the Waterlily House, where it is usually on display for most of the summer.

Pressed and dried specimens of rice are held in the Herbarium, one of the behind-the-scenes areas of Kew. Details, including images, of some of these specimens can be seen on-line in the Herbarium Catalogue.

There are 130 specimens of O. sativa in the Economic Botany Collection, including paper, brushes, starch, flour, seed, toasted rice and medicines produced from rice.

GrassBase - The Online World Grass Flora – Oryza sativa

Flora Zambesiaca – Oryza sativa

More about rice on Kew's Plant Cultures website

Kew education resources - rice information sheet

Sponsor a Marianne North painting - Rice harvest, near Bandong, Java