A nut is a type of fruit. Like all fruits, a nut develops from the ovary of a mature, fertilized flower. A nut is thick, dry, hard, and partly or entirely enclosed by a husk. A nut is indehiscent, in that it does not open along a naturally occurring seam, and remains closed even when fully mature.
A nut is a simple fruit, in that it is derived from the pistil of a single flower. Although a nut contains only one seed, the flower from which it develops has a compound ovary, with many ovules (immature and unfertilized seeds). Following fertilization, the other ovules of the flower undergo spontaneous abortion and die.
Familiar nuts include acorns, hickory nuts, walnuts, and beechnuts. The word nut is also used mistakenly to refer to the seeds or fruits of some other plants. Thus, pine nuts and peanuts are really seeds and not nuts. Brazil nuts and coconuts are really a different type of fruit, technically referred to as drupes, and not nuts.
Most nuts have a large concentration of protein, and are an important food source for wildlife. Humans often eat nuts as well. Formerly, Native Americans would leach out the astringent tannins from acorns so they could be eaten. North Americans once prized the nuts of the American chestnut (Castanea dentata) as a food. However, these trees have been decimated by an introduced fungus, known as the Chestnut blight. Now, nuts of the sweet chestnut tree (Cadtomea sakua) are occasionally served instead.
Peter A. Ensminger