Rice grains can exhibit large variations with respect to differing varieties. Anatomically, rice grains vary in the grain length, grain shape, translucency and the chalkiness. Many of the other variations in rice plant, and the rice grain specifically, involve genetic differences which are not always anatomically noticeable, such as pest resistance or temperature tolerance. Additionally, certain grain qualities are actively bred for by the crop community to enhance the ability to harvest rice.

Notice the variety that can be seen in these rice grains which were harvested from the same plant. The grains appear in varying sizes and shapes.

Grain length and shape are simple, visual ways of categorizing the rice grains based on their relative size. The grain length can be categorized as extra long (over 7.0 mm), long (between 6.0-6.99 mm), medium (between 5.0-5.99 mm) and short (less than 5.0 mm). The grain shape refers to the grain length to width ratio; and are categorized as slender (ratio greater than 3.0), medium (ratio between 2.1-3.0), bold (ratio between 1.1-2.0) and round (ratio less than 1.1). These guidelines are not exact, there is variation among the rice community as to an exact scale with which to judge the rice grains. "Grain length and shape are quantitatively inherited. the F1 is typically intermediate between its parents in size...grain size is highly heritable in most environments although low temperature after flowering can slightly reduce grain length." (Jennings, 1979; pg. 104)

This rice grain could be described as being in either the long or extra long range, and the shape as being either slender or medium.

To learn more about the internal anatomy of the rice grain, visit the grain anatomy page.
The grain translucency and chalkiness refer to the visual characteristics of the grain. Translucency is the color of the endosperm. It is rated as clear, intermediate or opaque. The chalkiness refers to the presence or absence of a white belly, white center or white back. These terms are often grouped under the simple title of white belly. the presence of a white belly in the rice grain is due partially to the genetic makeup of the variety, but is also due to the "temperature immediately after flowering; high temperature increases white belly while low temperature decreases or eliminates it." (Jennings, 79: pg. 101) The environmental effect can distinctly alter the interpretation of the chalkiness of the grain not due to the genetic makeup of the plant species.

The white belly pictured here can be difficult to see, try examining a rice grain yourself to notice the irregularities in the grain color.

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