- Oryza sativa is an annual, herbaceous monocotyledonous plant. It typically grows to a height of 0.4 to 1.5 meters, depending on the variety and growing conditions.
- It exhibits the characteristic morphology of grasses, with slender, erect culms (stems), hollow internodes, and nodes that are sometimes slightly swollen.
- The leaves are alternate, simple, and linear-lanceolate in shape, typically 20–100 cm long and 1–2 cm wide. Each leaf consists of a sheath, ligule (membranous or hairy), and a prominent, tapering blade.
- The plant has a fibrous root system adapted to both aerobic and anaerobic (flooded) conditions.
Inflorescence and Flower
- Rice produces a terminal panicle inflorescence, 15–30 cm long, which may be either open or compact depending on the cultivar. The panicle is made up of numerous spikelets, each borne on a pedicel. Each spikelet typically contains a single floret.
- The rice flower is small, bisexual, and wind-pollinated (anemophilous). It has two lodicules (modified perianth structures), six stamens with prominent, versatile anthers, and a single ovary with two feathery stigmas which aid in pollen capture. Anthesis usually occurs early in the morning, and fertilization is completed within a few hours.
- Self-pollination is common in O. sativa, though cross-pollination can occur at low frequencies.
Fruit and Seed
- The fruit of rice is a caryopsis—a dry, one-seeded fruit typical of grasses—commonly referred to as a grain. The seed is enclosed by a husk (lemma and palea) that remains attached at harvest in rough rice. Upon milling, the husk is removed to produce brown rice (with bran intact), and further polishing yields white rice.
- Rice grains vary widely in size, shape, and color depending on the variety. Grain length and width are key classification traits: short, medium, or long-grain.
- Wild and pigmented rice types may display red, purple, or black seed coats due to anthocyanin or proanthocyanidin content.
Special Characteristics and Adaptations
- Flood Tolerance: Rice is uniquely adapted to grow in submerged or waterlogged conditions. Specialized tissues called aerenchyma facilitate oxygen transport from shoots to roots.
- Photoperiod Sensitivity: Some landraces are highly sensitive to day length, flowering only under specific light conditions, while modern cultivars may be day-neutral.
- Genetic Diversity: O. sativa has two major subspecies: indica (long-grain, tropical) and japonica (short-grain, temperate), with numerous ecotypes adapted to upland, lowland, rainfed, and deepwater environments.
- Wild Relatives: The Oryza genus contains over 20 species, including Oryza rufipogon and Oryza glaberrima (African rice), which are important for breeding disease resistance and stress tolerance.
Reproductive Cycle and Growth Stages
- The rice life cycle spans approximately 3–6 months, depending on the variety:
- Germination and seedling establishment
- Vegetative growth (leaf and tiller development)
- Reproductive stage (panicle initiation, flowering)
- Grain filling and maturation
- Harvesting
