A family of hardwood trees containing about 1000 species but only eight genera. However these include Quercus (oaks), Fagus (beeches), Castanea (chestnuts), and Nothofagus (southern beeches), which together make up a large proportion of the broad-leaved forests of the world. It is probable that, in terms of biomass, this is the most abundant family of flowering plants. Representatives are not, however, found in the equatorial rain forests of Africa and South America. The flowers are unisexual and usually borne in catkins or spikes. The fruit is a nut, which is partly or completely enclosed within a *cupule
. Certain species of chestnut, especially sweet chestnut (C. sativa), are grown for their fruits. However timber, obviously, is the most economically important product of this family and, on a far smaller scale, certain species of oak yield cork (Q. suber) and tannins. Many species are grown as ornamentals.