RICE TAXONOMY AND BOTANY | MARTINS LIBRARY

         Rice is the grain with the second highest worldwide production after maize (Boumas, 1985). The domesticated rice comprises two species of food crop in the Poaceae (true grass) family Oryza sativa and Oryza glaberrima (Linscombe, 2006). These plant are native to tropical and subtropical Southern Asian and South Eastern Africa, respectively (Linares, 2002).

            Rice is grown as a monocarpic annual plant, although in the tropical areas it can survive as a perennial and can  produce a ration crop and survive for up to 20years (Boumas, 1985). It is also an important crop in sub tropical and temperate zones, the yield being higher in temperate areas than in the tropics (Boumas, 1985). It can grow up to 1- 1.8 m tall, or more depending on the variety and soil fertility. As a member of the grass family, rice has long, slender leaves between 50- 100cm long and 2-2.5 cm broad. The small mind pollinated flowers are produced in a branched arching to the pendulous inflorescence 30- 50 cm long. The edible part of the rice plant is the rice grain which is a caryopsis 5–12 mm long and 2-3 mm thick, and which includes glumes, endosperm, and embryo (Boumas, 1985). Some varieties even have awns at the tips of the grain. The awn is some times very long on certain varieties, so that special machines are required to break off and remove the awns prior to the de-husking of the paddy (Belsnio, 1980).

            According to Li (2003), rice grain is described as rough rice or paddy, consisting of brown rice (or caryopsis) and the hull. Brown rice consists of the endosperm, embryo and several thin layers of differentiated tissues – the pericarp (the ovary wall), the seed coat and the nucleus. Li (2003) further suggested that the seed coat consist of six layers of cells, with the aleuronic layer, being the innermost. The embryo contains the embryonic leaves (plumule), enclosed by a sheath (coleoptiles) embryonic primary root (radical), unsheathed by the coleorhizae, and the joining part (mesocotyl). According to Ihekoronye and Ngoddy (1985), the grains of rice consist of the endosperm, the main starchy portion, and the embryo or germ, which are separated by the scutellem. These are shown in Figure 2.1. Rice endosperm consists mostly of starch granules in a proteinaceous matrix, together with sugar, fats crude fibre and organic matter. The proximate compositions of rice endosperm are;

Table 2.1: proximate composition of rice endosperm

Source: Ihekoronye and Ngoddy 1985

Hull weight is about 20% of the total grain weight. The hull of some rice grains has the palea, lemmas, and richilla, while others have rudimentary glumes and perhaps a portion of the pedicels. The lemma is usually tough, archmenlike, sometime awned, and bigger than the palea. Grain ripening stage (15-65 days) can be subdivided into milky, dough, yellow- ripe, and maturity stages based on the texture and color of the growing grains. According to Hammer- Moister (2008), knowledge about grain quality starts with knowing the anatomy of a single grain, whether the grain is to be used for feed or for human consumption.