The Horse chestnut is easily recognized, with distinctive palmate leaves and an autumnal crop of conkers.  It was introduced from Turkey around the 1600s, and is a common tree in parklands and towns, but occurs less often in woodland.

Identification: Tree shape

The tree grows up to 40m tall and has a wide, domed canopy with foliage coming low down the tree.  Trees live up to 300 years.  It grows fast in most soils, and needs plenty of space.

Identification: Leaves

Horse chestnut leaves are palmate, consisting of 5 – 7 sharp-tipped leaflets arranged like the fingers of an outstretched hand.  Each leaflet can be 30cm long, making for impressively large leaves.

The leaf margins are toothed, and each leaflet has clear alternate lateral veins.  They’re a rich green colour.  For more on leaf margins click here.  For a blog on compound vs simple leaves click this link, and tips on leaf shape can be found here.

Identification: Flowers

The flowers of the Horse chestnut grow in a clustered tower of up to 50 flowers, known as a panicle.  These are sometimes referred to as candles.  Branches of the panicle are longer at the base than the top, creating a cone shape.  The uppermost flowers are male, those in the middle are both sexes, and the lowest ones are all female.

 They have a distinctive shape with bilateral symmetry.  Each flower is 9-11mmm long and has 5 fringed white petals, with a yellow patch at the base.  Once pollinated, this turns from yellow to dark pink.  This may communicate to visiting insects that the flower is no longer worth visiting as it has ceased providing nectar post fertilization.

Identification: Fruit

Horse chestnut seeds are known as conkers.  Only 5 or so flowers per panicle develop into conkers.

The conker is instantly recognizable.  Encased in a pale yellow-green, spiked case; conkers are a shiny mahogany brown.  This type of seed is known as a capsule by botanists.  (For more on seed types, check out my blog.)

There are 1-3 conkers per fruit, released when the seed case splits three ways at maturity.  Each is up to 4cm across, with the entire fruit measuring up to 7cm

Identification: Bark and buds

The bark is pinkish-grey and thin in young trees, becoming grey-brown and scaly with age.

Buds are distinctive and grow on stout hairless twigs.  They are a rich reddish brown, oval, and very sticky.  Lateral buds are opposite.

When the leaves shed, they leave a distinctive horseshoe-shaped scar.  This could be the source of the tree’s name; although some suggest it relates to the curative flour, made from ground up conkers, that used to be fed to horses.

Similar species

The Indian Horse chestnut, Aesculus indica, native to the Himalayas, is the only similar species.  Like the Horse chestnut, it is planted in parks and public spaces.

However, it follows in June rather than April to May and is a less robust tree.  Indian Horse chestnut conkers are small, dark brown and wrinkled, and held in smooth green seed cases.

History: Folklore

Because the tree was introduced to the UK comparatively recently, there’s not a great deal of folk lore associated with it.

However, the conkers are threaded onto strings and used to play – wait for it – conkers.  The first recorded game occurred in 1848 on the Isle of Wight, although there’s evidence the game was played with other less suitable nuts prior to this.

 To play, you take it in turns to whack your opponent’s conker with your own, the aim being to smash your opponent’s conker to bits.  Baking, pickling in vinegar, and drying for a year or more are all methods thought to toughen up a prize conker.  To this day, kids in the UK play conkers every year (although some well-meaning schools have banned the practice because it’s deemed dangerous).

One foot note is that some think keeping conkers in a room discourages spiders.  My studio has an open box of conkers and a plethora of friendly spiders, so I remain unconvinced.

History: Mankind and Horse chestnut wood

The wood of the Horse chestnut is pale and light.  It is weak and is mainly used to make children’s toys and for carving.  As it’s absorbent, it is also used to make trays for storing fruit, and it was sometimes used to make light weight artificial limbs.

History: Food and Medicine

Conkers were ground up into flour in Victorian times, and used as a coffee substitute during World War 2.  The mildly poisonous nature of the fruit, and its limited appeal has made this practice obsolete.

Flower buds can be used as a substitute for hops in beer brewing

Medicinally, conkers were fed to cattle and horses by Turkish soldiers in the 1600s to cure respiratory disorders.

Varicose veins, haemorrhoids, sprains and bruising can all be treated with Horse chestnut creams which thin the blood.  This makes it harder for blood to leak from veins and capillaries, and is useful in the treatment of water retention and oedema.  Aescin seems to be the active compound at work here, both for animal and human ailments.

Finally, the high levels of saponin made them good for making soap, after crushing and soaking the conkers in boiling water.  They are considered useful as moth deterrents by some.

Horse chestnut and Wildlife

The profusion of flowers provide a welcome treat to pollinating bees in late spring, and the caterpillars of the Triangle moth Trigonodes hyppasia feed on the leaves.

The larva of the Horse chestnut leaf mining moth Cameraria ohridella also feed on the leaves, the caterpillars are part of the diet of birds like the Bluetit.

Threats

Two pests and diseases have taken a firm hold of the Horse chestnut population recently.

The first is the Horse chestnut leaf miner mentioned above.  This insect burrows through the leaves, eating as it goes.  It can make entire trees look ill with blotched, yellowing leaves.  The good news is that there’s little evidence that the caterpillars do any lasting damage, merely altering the appearance of the tree.

The second is Horse chestnut bleeding canker, a more serious threat.  This bacterial infection damages the wood and bark, blocking the tubes of the phloem, making it impossible for the tree to carry water and nutrients.  This eventually kills the tree.

Signs of the canker include oozing dark patches on the trunk, discolouration of the wood, and chunks of bark peeling away.  This canker is becoming more common since it was first noted in the 1970s, and now infects more than 30% of English Horse chestnuts.

Trees also suffer leaf blotching caused by the Guignardia fungus, and are prone to scale insect infestations.

Conclusion

With their beautiful candles of flowers and ornamental stature, Horse chestnuts are handsome trees.  Although of limited practical or culinary use, they are vital to parkland and gardens.  One can but hope that the threats posed by canker and pests don’t end up reducing the population of these trees too seriously.

Online sources for this blog include websites of the Woodland trust, Trees for life, Totally wild, the Tree guide UK, and NatureSpot.  Reference books for this blog include the excellent The Greenwood Trees by Christina Hart-Davies  , and the Reader’s Digest The Field Guide to the Trees and Shrubs of Britain (out of print but commonly available second-hand).  I also referred to The Tree Forager by Adele Nozedar and The Living Wisdom of Trees by Fred Hageneder.

The post Trees: Horse chestnut Aesculus hippocastanum appeared first on Lizzie Harper.

Reasons why botanical terminology helps

I think knowing what variety exists in nature helps you to understand what you’re drawing.  So I thought I’d share some botanical terminology with you.  The terms discussed are in bold text; the examples are all illustrations I’ve done over the years.  If you find any mistakes feel free to tell me, I’m no botanist, just a keen and interested amateur.

 Leaves and their anatomy: Things to consider

When illustrating plants you need to consider: the leaf structure, its shape, its margins, its venation, and the position of the leaves in relation to one another and the stem.

This would result in a frighteningly long blog.  For today I’ll just discuss compound vs simple leaves, and some basic shapes of simple leaves.

Compound and Simple leaves: Which is which?

First, establish whether your leaf is simple, (in one piece) or compound (subdivided into smaller leaves).  Each of these smaller divisions is known as a leaflet.   A good trick here is to look for a bud.  Buds only occur at the junction of a leaf stem (petiole) and the main stem.  They never appear at the base of  a leaflet’s stem (called a rachis).  This is shown in my illustration of different forms of compound leaves below.

Compound leaves

Compound leaves and simple leaves come in a wide variety of shapes.  For example; a chestnut leaf, spreading its hand-like shape, is a compound leaf.  It is made of 5 to 7 leaflets, all anchored centrally.  The little leaflets are arranged a little like the fingers of a hand, hence the term palmate.

A leaf from the clover family (represented here by the bird’s foot trefoil) consists of three little leaflets, again, attached to one central point.  The term translates the English “three-leaved” into latin terminology: trifoliolate.

Sometimes, what appears to be a branch or sprig of leaves are, in fact, one leaf composed of many leaflets.  This is true of the ash.

Look for the bud at the junction of the leaves if you’re confused

Confused?  Use the trick of searching for the bud.  It’s at the junction of the sprig with the stem, you never see a little bud at the base of an individual leaflet.  This array is called pinnate, and in this case it’s an odd pinnate example since there’s one leaflet at  the tip without a pair.  You can also get even pinnate leaves (like the mimosa) where every leaflet has a pair, including at the tip of the rachis.  Just to make things even trickier, if each leaflet is divided again (stay with me, and picture an acacia, if you can) this is called doubly compound, or bipinnate.

Simple leaves

You’ve established your leaf is not compound.  If there is a bud to be seen, it’s at the base of the leaf stem.  Your leaf is simple.  But your life is not; because all leaves are by no means alike.  There’s a vast amount of shape variation amongst leaf shape (and a bit of variation between botanists who sometimes use different terms for these shapes.  In this blog, my references are Botany: A functional Approach by W. Muller, and Botany: A Textbook for Colleges by Hill, Popp, and Grove.)

The easiest shape to identify is Linear, or line-like.  Lavender and rosemary are examples.

A cordate leaf is somewhat heart-shaped; mulberry and lime are examples.

Ovate leaves are egg-shaped, with their base a little wider than their middle and their tip a little thinner than the middle; as with the beech leaf.

A lanceolate leaf is a very narrow ovate (egg-shaped) leaf; it tends to be at least 6x longer than it is wide.  Willow leaves are lanceolate.

Elliptical leaves are widest in their middle and taper evenly on either side of this.  Mint, cherry, and sage leaves are examples.

Oblong leaves are broad and un-tapered.  An example is the olive, and rhododendron.

Simple leaves: An overview

Here’s the overview of simple leaf shapes in one image:

There are many other leaf shapes, such as orbicular, rotundifoliate or peltate (all terms relate to leaves which are round, like a nasturtium) and sagittate (like an arrow) to name but two.  (For further discussion and examples, please follow this link from the University of Maryland.)

From the remit I had in doing the illustrations for The Rodale 21^st Century Herbal, this is most of what I examined.  I hope some of it helps people as much as it has helped me.

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