Horse-chestnuts & Buck-eyes
What are they?
These trees were for a long time considered members of their own family, the Aesculaceae, but the results of recent research have seem them moved into a larger family - the Sapindaceae - along with a number of other trees, including the maples. Horse-chestnuts are typified by their palmate leaves with fingered leaflets cut more or less to the base, as well as by their upright heads of showy flowers. The Common Horse-chestnut is well-known to school children as the provider of 'conkers', the name given to their rich, chestnut-brown seeds that are contained in a fleshy case. In recent years, Common Horse-chestnuts have become heavily infested with a leaf-mining moth, which sees the leaves turning brown and looking rather unslightly from late summer into autumn, but it does not appear to be having a major detrimental affect on the trees. Horse-chestnuts get their name as their seeds rather resemble the seeds of the true chestnuts, but they are unrelated and, indeed are inedible to humans and potentially even poisonous if eaten.
Where are they found?
These are all introduced species of trees, grown as ornamentals in parks, churchyards, along streets and in other amenity areas. Common Horse-chestnut germinated readily from seed and odd plants in hedgelines or woods may originate from seeds buried by squirrels.
Identification
The trees are most readily told from each other by their flowers, so flowering time is the best time to investigate them. However, there are subtle differences in the leaves and fruits and even winter buds, so most trees can be identified if attention is paid to these features.
Common Horse-chestnut Aesculus hippocastanum
Introduced from South-east Europe. Very common as an amenity tree along streets and in open spaces and widely found as specimens in hedgerows and shelter belts. Flowers late April to early June. A well-known and spectacular tree when in flower, with large 'candlesticks' of white flowers that have red and yellow centres. Sometimes grown in a double-flowered form which does not produce fruits and is considered preferable for roadside plantings. Leaflets broadest about two thirds of the way from the base. Winter buds large, long and very sticky.
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Red Horse-chestnut Aesculus carnea
Originated as a hybrid in cultivation but doubling of the chromosomes has produced a 'new' species that comes true from seed. Common as an amenity tree along streets and in open spaces and occasionally found as specimens in hedgerows. Flowers May to June. Leaflets shinier and more irregular in shape than those of Common Horse-chestnut; broadest about half way from the base. Winter buds large, rounded, not sticky. Seed cases less spiny than those of Common Horse-chestnut.
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Indian Horse-chestnut Aesculus indica
Introduced from the Himalayan region. Uncommon as an amenity tree along streets and in open spaces. Flowers June to July. Flower spikes more open than those of Common Horse-chestnut and without frilled edges to the petals. Leaves with elongate leaflets that typically have a drooping growth style. Winter buds short and rounded, slightly sticky.
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Yellow Buck-eye Aesculus flava
Introduced from North America and recorded as planted specimens in three sites in Suffolk. Flowers May to June. Flowers greenish-yellow, relatively small and narrow. Leaves with narrow, often slightly twisted or undulate, leaflets.
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Pride-of-India Koelreuteria paniculata
Introduced from China as an ornamental tree. Occasionally found where planted in amenity areas and recorded a handful of times as a garden escape in urban areas. Flowers July to August. Spectacular when in flower, with large panicles of brilliant yellow and orange flowers, followed by bunches of inflated fruits. Leaves pinnate with deeply toothed leaflets.
Note: Pride-of-India is not a buck-eye or horse-chestnut but is distantly related to them. The showy panicles of flowers can look similar from a distance but the leaves are very different.
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