plastid An organelle that is believed to have evolved from an autotrophic (see AUTOTROPH) endosymbiont early in plant evolution. Plastids occur in a variety of morphologies, including chloroplasts, chromoplasts, and leucoplasts, which are capable of being interchangeable. (Chloroplasts can develop into chromoplasts, and leucoplasts into chloroplasts.)

plastid An organelle within a plant cell, often occurring in large numbers. Apart from the nucleus, plastids are the largest solid inclusions in a plant cell. For convenience they are classified into those containing pigments (chromoplasts) and those that are colourless (leucoplasts), although changes from one to the other frequently occur. Plastids develop from proplastids, colourless bodies found in meristematic and immature cells; they also arise by division of existing plastids. See also chloroplast.

plas·tid / ˈplastid/ • n. Bot. any of a class of small organelles, such as chloroplasts, in the cytoplasm of plant cells, containing pigment or food.

plastid Type of organelle (specialized structure) found in the cells of plants and green algae. Chloroplasts and leucoplasts are two examples of plastids, which have a double membrane and contain DNA.