Someone had recently posted a question on AtlasQuest on a discussion board about chestnuts, about what they look like and if horse chestnuts were edible. I referenced a few books and answered the question, and then decided to go out and get some nuts.
First up, we will look at edible chestnuts. American chestnut (Castanea dentata) is native to North America. Unfortunately, many were devastated by a fungus introduced in the late 1800's from Chinese chestnut trees being imported. It is thought that three billion trees were killed. American chestnut still grows in the northwest, some pockets in Michigan and New Jersey, and throughout Appalachia. Another name for native American chestnuts is chinquapin. It is very difficult to distinguish American chestnut from Chinese chestnut (Castanea mollissima), and they often hybridize with each other. Both trees have green, sharply toothed leaves, the C. dentata more so than the C. mollissima. The flowers are produced in yellow-white catkins in spring, with a somewhat offensive odor. The nuts are encased in an incredibly spiny burr, that will open to drop the nuts soon before the first frost. Nuts from both trees are edible, although C. dentata is said to be sweeter. One of the few distinguishing characteristics is the twig buds. On C. dentata, the buds are smooth, on C. mollissima the buds are downy. It apppears we found a Chinese tree. The nuts had already released from the burrs, and we could see the ponty end with a hairy tuft and the oblong lighter spot on the other side of the nut. We grabbed a few nuts and brought them home to roast. Before roasting them in a very hot oven at 400°, I scored an "X" on the bottom of each nut to prevent them from exploding. The nut is covered by two skins, the leathery, brown outer hull, and a papery skin under the brown hull. Chestnuts contain very little fat compared to other nuts, and almost have a starchy taste and texture from their high carbohydrate content. You may have had them in stuffing during Thanksgiving. American chestnuts were an important food source for early settlers before the blight. The wood was good for houses and barns. Many animals like deer and turkey also relied on the chestnut. New, blight resistant American chestnuts are being developed, in hopes to re-establish the species, and fill a demand for the nuts.
Next is the horse chestnut (Aesculus). There are some North American species, referred to as "buckeyes", and European species referred to as "horse chestnuts". The leaves are large and palmately divided into 5-7 leaflets. The flowers are showy in spring, arranged in a panicle. They mature into a round, sometimes spiky hull with 1-3 nuts inside, each nut having a large, white scar--the "eye" of a buckeye. There is no hair or tuft on these nuts like the edible nuts. I think we found a European tree(Aesculus hippocastanum), with the spiky hull. This late into October, it was nearly impossible to find any nuts on the ground. Aesculus nuts are poisonous to consume, containing alkaloid saponins and glucosides, although deer can eat them safely. In Europe, the nuts (which are botanically seeds) were used for whitening hemp, flax, silk, and wool. We have heard of an unsporting method of crushing the nuts and placing them in a pond to slightly poison fish into a state of paralysis for easy gathering. The nuts are pretty, but do not eat these! There are several trees at Harkness Park in Waterford, Connecticut, probably planted as ornamentals. The nuts are used to play a game called "Conkers" which involves stringing the nut and swinging at your opponent's nut with the objective of breaking it.