Chessie Season

Flowers of the Horse Chestnut, Aesculus hippocastanum, in May

The Horse Chestnut, Aesculus hippocastanum, is an introduced deciduous tree originally used for decoration in avenues and gardens but now naturalised in woods throughout Ireland (Phillips, 1977 Wild Flowers of Britain pp. 38, 174) where it makes an attractive component of the country's hedge banks (O'Mahony, 2009 Wildflowers of Cork City and County p. 54). It is indigenous to the Balkan Penninsula and was brought to Vienna in 1576, via Constantinople, and onwards to Central and Western Europe (Avtzis et al., Sofia 2007 Phytologia Balcanica 13 pp. 183–187). It has a spreading habit and produces spikes of white to red flowers in April and May (Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 182). The leaves are bright green and divided into 5-7 oval leaflets. A. hippocastanum is among the first trees to turn brown in the autumn.

Leaf of The Horse Chestnut, Aesculus hippocastanum

It is, however, because of its fruit that A. hipposcastanum is best known. These consist of a fleshy outer part that is usually covered in spikes and a glossy brown nut, commonly called conkers, chestnuts or 'chessies'. These were very mush sought after when I was a child and are used to play the game of Chessies (more commonly called Conkers). This involves drilling a hole in the chessie and threading a piece of string or shoe lace through it. One then challenges an opponent and both players take turns to crack the other's dangling chessie with one's own. The winner is that who cracks the others chessie. All sorts of underhand schemes were employed to become the victor, such as yanking the opponent's chessie from their grasp, throwing it to the floor and stamping on it and treating the nuts to make them stronger. Some of these preserving methods are outline by O'Hare and Gerrel (2000, New Scientist: The Last Word 2 pp. 7-11), including baking in the oven, pickling in vinegar, varnishing and even soaking in hand lotion.

Fruit of the Horse Chestnut, Aesculus hippocastanum, in September

Unfortunately A. hippocastanum in Europe is now under threat from a bleeding canker disease which causes bleeding cankers on the stem and branches, foliar discoloration, and crown dieback often leading to tree death (Green et al., 2010 PLoS ONE 5: e10224). This disease was first reported in 2002/3 and has since infected hundreds of thousands of European A. hippocastanum trees across several countries in northwest Europe (Forestry Commission, 2008 Report on the National Survey to Assess the Presence of Bleeding Canker of Horse Chestnut Trees in Great Britain). The causative agent is the bacterium Pseudomonas syringae pathovar aesculi. This pathogen is identical to a P. syringae pathovar that infects Indian horse chestnut (Aesculus indica), indicating that it has found a new host in A. hippocastanum - one in which it is aggressively spreading.

Fruit of the Horse Chestnut, Aesculus hippocastanum