Horse chestnuts, water chestnuts and Brazil nuts are not chestnuts at all
Only trees of the genus Castanea, cousins of oaks and beeches, bear true chestnuts. Horse chestnuts are mildly poisonous lookalikes, water chestnuts are sedge tubers, and Brazil nuts are unrelated. The real thing arrives inside a burr so spiny it often opens only after falling to the damp ground.
Chestnuts are deciduous trees and shrubs native to temperate parts of the Northern Hemisphere, in four main groups: American, European, Chinese and Japanese. Sizes vary enormously. The European sweet chestnut can reach 35 to 36 metres and the American around 30, while Japanese trees average about 10 m and some chinkapins stay shrubby. Old bark turns thick and furrowed, the grooves twisting around the trunk like the strands of a great cable.
Every tree carries two kinds of long catkins. Some are purely male and mature first; others also bear small clusters of female flowers near the twig. The pollen has a heavy, sweet smell some people find unpleasant. Because the flowers cannot fertilise themselves, two trees are needed, and all Castanea species hybridise readily. The fruit sits in a very sharp burr 5 to 11 cm across holding one to seven nuts, which splits into two or four sections when ripe, helped by soil moisture.
Each nut has a hard shiny hull and a thinner inner skin, the pellicle, that clings to grooves in the creamy flesh. Varieties differ: American nuts are tiny, around 5 grams, but sweet and easy to peel, while some Japanese cultivars reach 40 grams with stubborn skins. Cultivars that reliably produce a single rounded nut per burr may carry the name marron, as in marron de Lyon. Chestnuts do not wait out a dormancy period and can sprout roots as soon as they land in autumn, but they lose viability quickly if they dry out.
The name comes from an earlier English chesten nut, from Old French chastain, Latin castanea and Greek kastanon. That Greek word may relate to the ancient town of Casthanaea in Magnesia, though the town was probably named after its trees. The tree appears twice in the King James Bible, including the story of Jacob placing peeled twigs in his flocks' watering troughs.
Source: Chestnut
