Monday, 19 June 2017

Horse Chestnuts

A little earlier on today I was strolling through Stefen Leys Pocket Park - or should I say ex-pocket park (its status has changed) when I was struck by the remarkable differences between the Common Horse Chestnut, Aesculus hippocastanum, native of the Balkans, and the rose-pink flowered Red Horse Chestnut, Aesculus x carnea. The flowers have long since withered and fallen but the differences are still distinct. On the former the spiny fruits are swelling, and will eventually hold the familiar conkers, much prized by us when  but now battling with computer games for the attention of children.
Developing fruits of Aesculus hippocastanum. Stefen Leys Pocket Park.
19 July, 2017

The fruits of the Red Horse Chestnut are immediately different, being virtually spineless but sometimes having a few blunt protuberances. Fruit are sometimes produced but the tree is a hybrid between Aesculus hippocastanum and the North American A. pavia. The unreliable nature of the fruits are perhaps the main reason why it is often grafted on to the Common Horse Chestnut.
The more oval fruits of Aesculus x carnea. Stefen Leys Pocket Park,
Daventry. 19 July, 2017
But it was not the nature of the fruits which made me pause but the foliage. The leaves of the Red Horse Chestnut gave no cause for comment and no surprise; they were unblemished and much as I remember them from my youth.
The leaves of Red Horse Chestnut are unblemished.

But the Common Horse Chestnut leaves were in a disastrous condition. The depredations of the moth, Cameraria ohridella, known as the Horse Chestnut Leaf Miner, had wrought havoc.
Horse Chestnut leaves are in a dreadful state.
This tree has been described as 'Possibly the most beautiful of large flowering trees hardy in the British Isles' (Hilliers' (sic) Manual of Trees and Shrubs). Now I suspect no one plants this species as the moth, only known in the British Isles since 2002, has apparently spread to all parts of the U.K. At least sixteen species of parasitoid wasps attack the moth larvae but their effects are minimal. However, as noted, the Red Horse Chestnut appears immune from attack and for owners of large gardens this species offers an alternative.
A close-up of the damage caused by Cameraria ohridella.
Stefen Leys Pocket Park. 19 June, 2017
Another option could be the Sweet Buckeye, Aesculus flava, from the south-east of the United States but this is not fully immune from attack either. What of Aesculus pavia? This is certainly a lovely species (I seem to recall seeing it in Oxford University Botanic Gardens) but is no more than a large shrub. Nevertheless, it's a thought.

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