Castanea sativa (Sweet chestnut)
Species: C. sativa
Binominal name: Castanea sativa
Synonyms: Castanea prolifera, Castanea vesca, Fagus castanea.
Common name: Sweet chestnut, Spanish chestnut.
Castanea sativa is a medium-sized long-lived deciduous tree native to the area stretching from the Balkan Peninsula to northern Iran where they have been cultivated for at least 3,000 years. Now is widely cultivated and naturalised throughout the temperate world. It grows up to 35 m tall, with a trunk up to about 2 m in diameter. The bark often has a net-shaped (retiform) pattern with deep furrows or fissures running spirally in both directions up the trunk.
The bright dark green leaves are oblong-lanceolate, 16–28 cm long and 5–9 cm broad with margins that are boldly toothed.
The catkins hold the flowers of both sexes, with male flowers in the upper part and female flowers in the lower portion. These catkins are 10 to 20 cm long and appear in New Zealand during November and December. Pollination is carried out by wind and insects. C. sativa trees require cross pollination from a different compatible variety to ensure good nut production. This means that an orchard planting must contain at least two different pollen producing trees. Trees that are not cross pollinated at all will still produce burrs every year but these will only contain 3 flattened empty shells lacking kernels, or on occasion poorly formed nuts.
The female flowers develop into spiny protective husks called burrs. In the northern hemisphere this prickly outer layer deters squirrels and other seed predators from getting to the nuts within them, before they are shed. Chestnuts fall in the autumn and ideally should be gathered every day over peak nut fall because of their highly perishable nature and their susceptibility to predation by possums and rats which relish the nuts.
Castanea sativa is widely cultivated for its edible nuts contained in prickly husks. Roasted chestnuts are a well-known Christmas treat in Europe. They are traditionally roasted in their tough brown husks after removing the spiny cupules in which they grow on the tree, the husks being peeled off and discarded and the hot chestnuts dipped in salt before eating them. Roast chestnuts are traditionally sold in streets, markets and fairs by street vendors with mobile or static braziers.
The skin of raw peeled chestnuts can be relatively easily removed by quickly blanching the nuts after scoring them by a cross slit at the tufted end. Once cooked, chestnuts acquire a sweet flavour and a floury texture not unlike sweet potato. The cooked nuts can be used for stuffing poultry, as a vegetable or in nut roasts. They are used for flour as they are nutritionally very similar to wheat, except for a lack of the protein gluten, a binding agent, so baked goods made with chestnut flour tend to have holes or a crumbly texture. They are also used as a cereal substitute, coffee substitute, a thickener in soups and other cookery uses, as well as for fattening stock. A sugar can be extracted from them. The Corsican variety of polenta (called pulenta) is made with sweet chestnut flour. A variety of Corsican beer also uses chestnuts. Another product is sold as a sweetened paste mixed with vanilla, crème de marron, sweetened or unsweetened as chestnut purée or purée de marron, and candied chestnuts as marrons glacés. In Switzerland, it is often served as Vermicelles. Roman soldiers were given chestnut porridge before entering battle.
The leaves of C. sativa are used in herbal remedies for coughs, whooping cough, diarrhea and rheumatism. A hair shampoo can be made from infusing leaves and the fruit husks. The leaves are rich in tannins and possess antibacterial and antifungal properties. Research has shown that C. sativa probably has allelopathic effects on other plant species growing nearby; that is, chemicals in the leaves that are released into the leaf litter of the forest floor inhibit the germination and the growth of other tree species' seedlings nearby.
Though this species is widely cultivated for its edible seeds it is also cultivated for its wood. This tree responds very well to coppicing, which is still practiced in Britain, and produces a good crop of tannin-rich wood every 12 to 30 years, depending on intended use and local growth rate. The tannin renders the young growing wood durable and resistant to outdoor use, thus suitable for posts, fencing or stakes. The wood is of light colour, hard and strong. It is used to make furniture, barrels (sometimes used to age balsamic vinegar), and roof beams notably in southern Europe (for example in houses of the Alpujarra, Spain, in southern France and elsewhere). The timber has a density of 560 kg per cubic meter, and due to its durability in ground contact is often used for external purposes such as fencing. It is also a good fuel, though not favoured for open fires as it tends to spit.
In New Zealand the nuts can be infected while on the tree with the fungal diseases Phomopsis and Botrytis (and other fungi) and this can lead to rotten nuts at harvest time and can cause serious losses even when stored in cool storage.
There is a native grass grub beetle that will eat the soft new season foliage of chestnut trees in the late spring when they fly at dusk. Young trees may be completely stripped.
Possums are especially damaging, eating the bark, leaves and breaking branches and eating the nuts when they fall to the ground at harvest. Rats also eat the nuts. Rabbits and hares will eat the bark of young trees.
The images on clicking will enlarge.
Photographed December at Smart Organics, Smart Road, New Plymouth.
The catkins which hold flowers of both sexes
The top surface of a leaf.
An old dried burr opened to show the nuts.