Horse Chestnuts

On a visit to Stefen Hill Pocket Park today the magnificent Horse Chestnuts, Aesculus hippocastanum, were impossible to ignore. Perhaps we take them for granted but, as people are generally aware, all is not well with our 'conker trees'.

Horse Chestnut trees, now fully in bloom, made a fine sight.

Stefen Hill Pocket Park. 24 April, 2020

The Latin name is of interest: hippocastanum needs no discussion as it simply means 'horse chestnut'; aesculus is a little more of a puzzle, for it was the Latin name for some sort of tree - possibly an oak - which bore edible nuts. In parkland the conkers are sometimes eaten by livestock with no adverse affect but they contain a glycoside, aesculin, which is dangerous if consumed by children in large quantities. However, the taste is bitter and it is hard to imagine children eating enough to cause anything other than a mild stomach upset.


A conker is, of course, the seed; the whole fruit is formed by the conker and its spiny casing. The curious fruit and the oddly shaped flowers led to this species, and its close relative such as the buckeyes of North America, being placed in their own family, the Hippocastanaceae. However, once again work on the DNA of these trees shows that they are better placed in the Soapberry Family, the Sapinadaceae, so they are now recognised as relatives of maples, including the sycamore.

The curious flowers of horse chestnut. The polen is pink.

Stefen Hill Pocket park, 24 April, 2020

Mention of the Soapberry Family reminds us that a soap can be made from the leaves of the Horse Chestnut or the conkers. Many recipes for this are on line but I don't think I'll be bothering


So what are the dangers facing this loveliest of trees? The IUCN (International Union for the Conservation of Nature) classes it as vulnerable to extinction. For some reason in its home, isolated mountain regions of the Balkans, it has been subjected to logging on a considerable scale. This is odd, for the timber is of limited use, being non-durable and not easy to work. Its principal uses seen to be for boxes and charcoal.


In Britain it can be affected by Bleeding Canker, caused by at least three species of micro-organism and causing the bark to bleed a dark, sticky fluid. However, the most serious threat, and the one with which most people are familiar, is that caused by the Horse Chestnut Leaf Miner, Cameraria ohridella. When I visited the pocket park today the foliage was in lovely condition but the moth was already present.

The Horse Chestnut Leaf Miner is already investigating leaves.

Stefen Hill Pocket Park, 24 April, 2020

It is quite a pretty moth and looks innocuous enough. It is however quite tiny and a challenge for my little camera, so I have included a professional job.

Horse Chestnut Leaf Miner, Cameraria ohridella.

Good news? Well, there is a glimmer. For a start a number of tiny wasps - about 18 in all - are parasites (parasitoids to be precise) upon the caterpillars and do a little to keep it in check (Ref. Pocock, et al). Then there is natural regeneration. Beneath just one tree in the pocket park I counted 16 saplings. If people nurture these and similar saplings there should be plenty to replace dead or moribund trees.




If all horse chestnuts are able to regenerate as prolifically as those in

Stefen Hill Pocket Park, the species should survive. 24 April, 2020

For the time being then, we can continue to enjoy the presence of this species, an enjoyment which will be shared by beekeepers, for the tree is a prolific source of pollen and nectar.


Reference


Pocock, M, Evans, D, Strawn N, and Polaszek, A  The Horse-chestnut Leaf miner and its parasitoids  British Wildlife, Vol. 22 No. 5