A seed is a mature ovule enclosing an embryonic plant, stored food material (in endosperm, persistent nucellus or embryo itself) and a seed coat formed by one or two integuments. In h broad sense the term seed is also applied to small one-seeded, dry fruits (e.g., grains of wheat or barley which are in fact made up by fusion of fruit wall and seed coat) or other disseminules (fruits with attached bracts, inflorescences or even vegetative structures such as tubers and bulbils). The size, shape, color and surface of the seed show innumerable variations. Most orchids have minute seeds like dust particles.
Seeds of a majority of flowering plants are a few millimeters in diameter (e.g., mustard, guava and poppy) or extend to a length of about a centimeter (e.g., castor, cucumber and groundnut). Some tropical trees and lianas have fruits with very large seeds. The double coconut, Lodoicea maldivica has bilobed seeds as large as 10 cm weighing nearly 6 kg. The seed surface may be smooth, wrinkled, striated, ribbed, furrowed or it may have a variety of patterns on it. The surface may be glossy (as in linseed and castor), fleshy or pulpy (in Magnolia) or covered with hair (in cotton).