According to the botanical definition, nuts are a type of dry one-seeded fruits that are indehiscent i.e. they do not split apart along a single seam once they have reached maturity. The pericarp (fruit wall) becomes hard at maturity. Examples are Acorns (in oaks), Chestnuts, Hickory and Hazelnuts etc.
In culinary terms, however, the word nut is used more broadly to include fruits, and even seeds, that are not botanically qualified as nuts, but those have a similar appearance and culinary role. Any large, oily kernel found within a shell and used in food may be regarded as a nut. The term nut is also used to refer to various hard-shelled fruits or seeds.
Thus both botanical (true) nuts and non botanical nuts (various hard-shelled fruits and seeds) are included in the list of culinary nuts.
Culinary nuts are:
- True nuts (dry indehiscent single seeded fruits): Acorns, Chestnuts, Hickory and Hazelnuts
- Seeds of Drupe fruit (fleshy fruit with a single stone or pit) also called as Drupaceous nuts: Cashew nuts, Brazil nuts, Coconut, Walnuts, Pecans, Almond, Pistachio nuts
- Seeds of Legumes (Dry dehiscent fruits): Peanuts
- Follicle (Dry unilocular dehiscent fruit): Macadamia
- Seeds of Gymnosperm: Pine nuts
Cashew nut is the seed of the drupe fruit which is kidney or boxing-glove shaped and grows at the end of the pseudo fruit.
The fruit (Capsule) of Brazil nuts has a hard woody shell, and inside contains 8–24 triangular seeds 4–5 centimeters long, packed like the segments of an orange; it is not a true nut in the botanical sense.
The Coconut is considered a dry fibrous drupe with a green, waterproof outer layer (exocarp), a thick, buoyant, fibrous husk (mesocarp) and a hard, woody, inner layer (endocarp) surrounding the large seed. The actual seed embryo is embedded in the coconut meat (endosperm).
Walnuts and Pecans are not true nuts but technically drupes, called drupaceous nuts. The husks are produced from the exocarp tissue of the flower while the part known as the nut develops from the endocarp.
Almond is the seed of the drupe fruit. The outer covering or exocarp of the fruit is a leathery grey-green coating (called the hull), which contains inside a hard shell, and the edible seed, commonly called a nut in culinary terms.
The Pistachio nut is the seed of thin walled drupe. The fruit has a hard, whitish exterior shell. The seed has a mauvish skin and light green flesh. The characteristic feature of the pistachio fruit is the semi-opening of the shell after maturity.
Peanuts are the seeds of the Legumes that are dry dehiscent fruits.
The fruit of Macadamia is a very hard woody globose follicle with a pointed apex, containing one or two seeds, dehiscing by the ventral suture in order to release seeds
Pine nuts are edible seeds of Pines which develop on the surface of cone scales, exposed to the environment.