Above a giant sweet chestnut tree, Castanea sativa (on the Fredville park estate, kent,
UK). I didn't take actual measurements, but the diameter of the trunk must be about 3 m.
buttresses to support the great weight. On the main branches, the younger bark
displays the typical spiral pattern of youth, so characteristic of sweet chestnuts, which
spirals either clockwise or anticlockwise up the tree.
Trunk. Also characteristic of old sweet chestnuts is the large diameter of the trunk
relative to the height. One of the neighbouring chestnuts had an open hollow bole, with
the dead heartwood burned away and it was easily large enough for several people to
stand inside. Chestnuts are renown for the thickness of their trunks, especially when
pollarded, and the thickest trunk in the world is thought to belong to a pollarded
chestnut in Europe (though the thickest species is in general the baobab tree of Africa).
They become to resemble living caverns more than trees and the trunks may eventually
split into a ring of separate trees.
Fruit. The sweet chestnut is a native of the Mediterranean region and the Romans
probably introduced the sweet chestnut to Britain for its nuts (seeds) which are quite
edible raw or cooked and can be made into flour or used as a coffee bean substitute.
Often, however, in the current British climate the fruit abort before become fully
developed and many are shed as hollow skins without accumulating any edible flesh.
The nuts usually occur in threes, enclosed within a green, fleshy and spiny fruit (cupule).
Leaves. The leaves are long, frequently up to 22 cm (9 inches) with sharply toothed
margins. Each leaf vein enters a tooth and emerges from it as a terminal bristle.
Flowers. Both male and female flowers are borne on the same slender, yellow upright
spikes (resembling pipe-cleaners) on the ends of the branches, with the female flowers
at the base and open in July. Male only catkins may also develop near the base of the
branch. Chestnut (and horse chestnut) trees are deciduous, shedding their leaves in
Autumn (Fall). The floral formula is typical of the Fagaceae, the family to which
Castanea belongs, along with Quercus (oak) and Fagus (beech).
Male: K(4-7) C 0 A 4-many G 0;
Female: K(4-7) C 0 A 0 G(3), inferior ovary.
Specifically, for Castanea sativa, Ronse de Craene (Floral Diagrams: an aid to
understanding flower morphology and evolution, 2010, Cambridge University Press)
gives the formula for the male or staminate flowers as: * K3+3 A3x3+3 G(3-sterile and
the female or pistillate flower as: * K3+3 A(all sterile staminodes)3+3 G(6), inferior
ovary. The male flowers spiral around the catkin axis and are grouped into bunches of
4-9 flowers. The female flowers occur in groups of 1-3.
Bark. The bark is smooth and greyish-green when young, becoming deeply fissured by
spiral grooves with age (each bark ridge/fissure often forms a clockwise or anticlockwise
spiral extending for several feet). Burrs are often formed high up in the bole (see
Wood. The wood is as strong and tough as oak, though more easily split. The sapwood
forms a thinner layer than in the oak and the medullary rays are very fine and hard to
see. It has been used in fencing, posts and stakes. The winter buds are yellow-green or
brown and alternate. The twigs are five-sided (angular) and vary from shiny olive-green
Sweet chestnuts grow well in the South-East of England, with the warmer summers and
the warm sandy soils. Here they are one of the dominant trees and are naturalised,
growing from seed.
Above: a montage of another ancient chestnut at Fredville, with 'elephant's feet'
or bulbous roots which have probably reacted to the mechanical stresses of the
weight of this slanting tree.
Above: the 'Step Tree' - an ancient
chestnut at Fredville, so-called because a
platform with steps leading up to it was
layered itself - embedding in the ground in
two places, with a new 'tree' growing from
the branch tip.
Above: more ancient chestnuts at Fredville
Above: close-ups of part of the upper bole
of one of the Fredville chestnuts. The
Fredville estate is privately owned, but part
of it is opened to the public where public
paths cross through it. Enclosed within the
private part is one of the largest oak trees
in England, Majesty (the Fredville Oak), but
permission from the owners must be sought
in order to visit the oak.
Click images to enlarge...
The Horse Chestnut
The name 'chestnut' applies equally to what is properly called the horse-chestnut, Aesculus hippocampus, an import from the
Balkans, introduced into Britain in the 16th century. Also called the 'horse chestnut' in native Turkey, the nuts (conkers or
obblyonkers) were fed to horses and used as horse medicine, acting as an anti-inflammatory to treat sprains and the like. The
horse-chestnut is in a different genus to the sweet chestnut and the two are quite different trees, though both encase their nuts in
green spiny cupules (which turns brown when ripe in the horse chestnut). Indeed Castanea belongs to the Fagaceae or beech
family, whereas Horse-chestnut belongs to the soapberry family, Sapindaceae, Usually only one conker occurs within each cupule.
Conkers are bitter and mildly poisonous, though they have been ground into flour and boiling water used to extract the bitterness.
Both conkers and sweet chestnuts are a rich 'chestnut-brown' in colour.
Originally introduced into private estates, by architects and land-scapers like capability Brown and Christopher Wren, the horse
chestnut was eventually introduced into towns and cities where the game of conkers became nationwide.
The leaves are consist of 5 to seven large leaflets with serrated margins, arranged in a palmate fashion on a central stalk. When teh
leaves dehisce (detach or are shed) they leave horseshoe-shaped scars on the twig, studied by teh sealed ends of vessels (like
'nails' in a horseshoe). Each leaflet broadens toward the tip before suddenly narrowing to a point, and may be up to 30 cm (12
The flower spikes are especially attractive, upright cones, like candelabras, with white or pink flowers. Each spike may exceed 30 cm
in height and bear more than 100 flowers. The tree may self-seed in Britain, but is not generally naturalised, being largely planted as
an ornamental. Each flower has a yellow blotch on its petals when newly opened, which turns crimson after pollination. this signals to
pollinating insects to ignore those flowers which have already been pollinated.
The bark is dark grey-brown and smooth in youth, dividing into irregular pink-brown scales with age. The wood is white and soft and
brittle. The trunk is often fluted and spreading or buttressed at the base.
Extracts from horse-chestnuts are used to make certain anti-inflammatory medicines. The active ingredient, found in the essential oil,
is the saponin aescin. Saponins are soapy compounds produced by many plants. Soaps are salts of fatty acids and so are
amphipathic molecules, meaning that they have one readily water-soluble end, the hydrophilic or 'water-liking' end and one
lipid-soluble hydrophobic or 'water-avoiding' end. This allows them to form micelles, tiny molecular spheres that can enclose
fat-soluble (and water-insoluble) 'dirt' (see lipids). Similarly saponins are amphipathic, and will also foam in water, producing micelles.
In this instance the hydrophilic part is formed of three glucose sugar-residues, whilst the fat-soluble hydrophobic part is a triterpine
derivative - a large planar molecule formed from cyclic hydrocarbons joined together.
Above: chestnuts of Castanea sativa. Photo credit: Fir0002/Flagstaffotos, Wikimedia
Commons. Of the three nuts, the one in the centre has aborted, failing to develop the enclosed
ovule and so appears flattened. No more than one ovule, and its enclosed embryo, develop in
each nut. Each nut is a whole fruit, the spiny cupule being developed from bracts. Aborted
fruits contain no seed, but air filled instead with silky hairs.
Terpenes are built from five-carbon isoprene units
(left). Two isoprenes make a monoterpene, six
make a triterpene. These terpenes may be linear
chain molecules, of they may become circularised
and undergo other modifications.
One of the drug-actions of aescin is to alter the
rate of synthesis of nitric oxide (nitrogen(II) oxide,
NO) in endothelial cells lining the lumens of small
blood vessels. NO is a key signalling molecule that
regulates vessel diameter (via smooth muscle cell
contraction) which is a key mechanism in the
In North America, 'chestnut' refers to the American Chestnut, Castanea dentata, a close relative of the European sweet chestnut
(Castanea sativa). The Chinese Chestnut, Castanea mollissima is also a close relative. The American Chestnut is a natural
woodland species, favoured for its nuts, though it is increasingly rare in the wild. The Chinese Chestnut is also grown for its nuts. All
are stately trees, reaching about 100 feet (30-35 m) in height.
Castanea belongs to the beech family, along with Fagus (beech) and Quercus (oak). Hardwood may be roughly divided into two
structural types, depending on the arrangement of the parenchyma rays: storied (stratified) and nonstoried (nonstratified) wood.
Recall the rays are short plates or strands of living cells that radiate from the centre of the trunk to the periphery. In storied wood,
the rays do not overlap vertically, and so form distinct horizontal layers or tiers down the trunk:
Examples of trees with storied wood include the horse chestnut (Aesculus), Ficus (fig) and Tilia (lime).
In nonstoried wood the rays overlap vertically with their neighbours, so that the tiers are indistinct:
Examples of nonstoried wood include the sweet chestnuts (Castanea), Quercus (oak), Juglans (walnut) and Fraxinus (ash).
Chestnut Trees (Castanea sativa)
Horse-chestnut (Aesculus hippocastanum) a member of the Sapindaceae
or soapberry family.