Latin name: Aesculus hippocastanum
Source material: Pollen
Common names: Horse chestnut tree, Common horse chestnut
The Horse chestnut tree is native to Europe and particularly common in the Balkans (northern Greece and Albania), and has become naturalised in Britain. It is now cultivated throughout temperate zones, including Mexico, Turkey and the USA.
Horse chestnut is a large, deciduous tree growing 17 to 30 m in height at a fast rate. The bark is mostly dark grey and brown, but exfoliates in plates on older branches and the trunk to reveal showy orange bark underneath. The leaves are large, with 5 to 7 toothed leaflets.
The tree flowers in May, and the seeds ripen in September. The flowers are borne on large, upright panicles; these flowers are white with a yellow blotch at the centre that fades to red after pollination. The flowers have a delicate honey-like scent, are hermaphrodite (have both male and female organs) and are pollinated by insects. The fruits produced are in pale-green capsules, which are covered with blunt spikes. The fruits mature in September and October. These prickly green nut cases containing shiny, brown, inedible Chestnuts are known as "conkers".
The tree is found naturally in woodlands but can be planted in gardens and streets.
The roasted seed is used as a coffee substitute or cooked and eaten. The seed is rich in saponins. The seeds have also been used as a decongestant, expectorant and tonic. Saponins in the seeds are used as a soap substitute. Saponins are toxic.
No allergens from this plant have yet been characterised.
An extensive cross-reactivity among the different individual species of the genus could be expected (1).
Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are possible following exposure to pollen from this tree; however, few specific studies have been reported to date (2-3).
Sensitisation to Horse chestnut tree pollen is common where the tree is growing. In an Austrian study, IgE antibodies to Horse chestnut pollen were found in 12.6% of urban children, compared to 1.9% of control subjects recruited from a rural area. Horse chestnut-specific IgE levels were highest in highly atopic pollen-allergic children, in particular those also sensitised to the Plane tree (2).
Contact dermatitis to the extract of Horse chestnut has been reported (4).
Yman L. Botanical relations and immuno-logical cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
Popp W, Horak F, Jager S, Reiser K, Wagner C,
Zwick H. Horse chestnut (Aesculus hippocastanum) pollen: a frequent cause of allergic sensitization in urban children.
Allergy 1992;47(4 Pt 2):380-3
Jaspersen-Schib R, Theus L, Guirguis-Oeschger M, Gossweiler B, Meier-Abt PJ. Serious plant poisonings in Switzerland 1966-1994. Case analysis from the Swiss Toxicology Information Center. [German] Schweiz Med Wochenschr 1996;126(25):1085-98
Comaish JS, Kersey PJ. Contact dermatitis to extract of horse chestnut (esculin).
Contact Dermatitis 1980;6(2):150-1