Chestnuts roasting on an open fire: thus begins Nat King Cole’s classic Christmas song. One has to hope that they were true chestnuts (edible) and not horse chestnuts (toxic). And the nuts do look much alike, even though the trees they come from are very different. It may be wise to learn to tell the two part.
Two Trees, Two Different Families
First, the two trees are in no way related. The chestnut (Castanea) belongs to the Fagaceae, the beech and oak family. The horse chestnut (Aesculus), long in its own family, the Hippocastanaceae, was recently transferred to the Sapindaceae, the soapberry family. But the nuts of chestnuts and chestnut trees do look very similar. In the long distant past, someone began calling one plant “horse chestnut”, because its chestnutlike nuts could be used to treat horses of respiratory ailments, and the name stuck.
Edible or Toxic?
That was probably not a good idea, as the true chestnut (Castanea) is edible while the horse chestnut is toxic and in my opinion, there should be no possible confusion between edible and toxic plants.
Besides being roasted over open fires and sold as roasted nuts on street corners, the chestnut can be used as turkey stuffing or turned into chestnut cream.
The horse chestnut (Aesculus), on the other hand, is slightly toxic to humans and many mammals, although not to squirrels or deer. Like many poisonous plants, it can have useful medicinal properties when properly prepared.
In Your Garden
Unless you’re a nut-grower, you’re unlikely to have a chestnut tree (Castanea) in your yard. Most species are big trees and are not considered terribly attractive. Besides, the very prickly burr (seed covering) is a major annoyance when it ends up on the ground in the fall. You certainly won’t want to step on it barefoot!
Also, in North America, the main native species, the American chestnut (C. dentata) was almost wiped out by chestnut blight (Cryphonectria parasitica), accidentally introduced from Asia in the early 20th century. As a result, many North Americans have never see a chestnut tree and their only encounter with chestnuts is likely to be through the roasted nuts offered on street corners or in supermarkets.
Europeans are more likely to have seen massive chestnut trees, as their own main native species, the common chestnut (C. sativa), grows widely throughout central Europe into Asia minor and was not decimated by the blight.
In gardens, though, as well as along streets and in parks, the horse chestnut is widely grown as an ornamental tree in both North America and Europe. The common horse chestnut (Aesculus hippocastanum), with its upright spikes of white flowers dotted pink, is especially popular, as are hybrids with pink or red flowers that come from crosses between A. hippocastanum and other species.
You may remember harvesting the nuts and using them to play conkers (a child’s game where they are hung on a string and banged together; the owner of the one that doesn’t break becoming the winner).
And there are other species of horse chestnut you sometimes find in gardens, notably Ohio buckeye (A. glabra), a medium-sized tree, and bottlebrush buckeye (A. pauciflora), a large shrub with white flowers. (The term “buckeye” is used for Aesculus species whose shell is spineless, as they are said to resemble deer eyes they split open.)
Telling Them Apart
Here’s an easy guide to telling chestnuts and horse chestnuts apart: