giant sweet chestnut tree, Castanea
(on the Fredville Park estate, Kent,
UK). I didn't take actual measurements, but the diameter of the
trunk must be about 3 m.
Note the buttresses to support the great weight and in particular
to keep the tree stable when subject to lateral forces such as
high winds. 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
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
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
Male: K(4-7) C
0 A 4-many G 0;
K(4-7) C 0 A 0 G(3), inferior ovary.
Specifically, for Castanea
Ronse de Craene (Floral Diagrams: an aid to
understanding flower morphology and evolution, 2010, Cambridge
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
male flowers spiral around the catkin axis and are grouped into
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
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
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
growing from seed.
montage of another ancient chestnut at Fredville, with 'elephant's
or bulbous roots which have probably reacted to the mechanical
stresses of the
weight of this slanting tree.
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.
more ancient chestnuts at Fredville
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.
images to enlarge...
name 'chestnut' applies equally to what is properly called the
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
green spiny cupules (which turns brown when ripe in the horse
chestnut). Indeed Castanea belongs to the Fagaceae
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
Both conkers and sweet chestnuts are a rich 'chestnut-brown' in
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
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
in height and bear more than 100 flowers. The tree may self-seed
in Britain, but is not generally naturalised, being largely
an ornamental. Each flower has a yellow blotch on its petals when
newly opened, which turns crimson after pollination. this signals
pollinating insects to ignore those flowers which have already
The bark is dark grey-brown and smooth in youth, dividing into
irregular pink-brown scales with age. The wood is white and soft
brittle. The trunk is often fluted and spreading or buttressed at
Extracts from horse-chestnuts are used to make certain
anti-inflammatory medicines. The active ingredient, found in the
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
derivative - a large planar molecule formed from cyclic
hydrocarbons joined together.
chestnuts of Castanea
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.
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
North America, 'chestnut' refers to the American Chestnut, Castanea dentata, a close relative of the
European sweet chestnut
The Chinese Chestnut, Castanea
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.
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:
of trees with storied wood include the horse chestnut (Aesculus), Ficus (fig) and Tilia
the rays overlap vertically with their neighbours, so that the
tiers are indistinct:
of nonstoried wood include the sweet chestnuts (Castanea), Quercus (oak), Juglans (walnut) and Fraxinus (ash).
Trees (Castanea sativa)
a member of the Sapindaceae
or soapberry family.