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A BIT OF FRUITY WINTER BOTANY
16/12/2021
I am sure most readers can name the majority of the fruits we see in winter. After all, many of them are familiar at Christmas as decorations or party food, but do you know how we classify them in botany? It is true that all berries are fruits but also true that not all fruits are berries. It is all more complicated than you might think, but here are a few notes which I hope will encourage you to delve more deeply into the botany of fruits. The mistletoe Viscum album has what we colloquially call berries, but the correct term for the fruit of this hemiparasitic epiphyte is a drupe. Drupes are stone fruit and are formed from one carpel. They have a single seed – squash a mistletoe berry and you will see. The seed is enclosed by three layers of tissue, a stony endocarp around the seed, a fleshy mesocarp and an outer “skin” known as an epicarp. If you read my recent note about the value of classics in biology, you will appreciate how Latin and Greek help understanding the technical vocabulary! Incidentally, if you do squash a mistletoe drupe, notice the stickiness of the flesh which has evolved to help it stick to host trees when birds which feeding on them, the mistle thrush especially, wipe their beaks on branches. The seeds then sprout and form the mistletoe plant which is technically a gall.
I still have a few raspberries Rubus idaeus sensu lato which I think originated from a late-fruiting variety I planted years ago called Terri-Louise. Like blackberries, and despite their common name, these are not strictly berries, but an aggregate of drupes known as drupelets. They originate from a single flower producing many fused carpels, the structures containing the ovules.
The Solanaceae (tomatoes, potatoes, nightshades etc.) are all true berries. Here are two examples, the upper being the edible fruit of Duke of Argyll’s teaplant Lycium barbarum, a Chinese native that has become naturalised in England, and the berries of which are still to be seen late into December. It can be found here and there in scrub and hedges. The lower berry is the false Jerusalem cherry Solanum pseudocapsicum, a familiar Christmas houseplant which is almost hardy. It is poisonous as are several of this family.
Another Christmas favourite is the holly Ilex aquifolium. Holly berries do not have a single seed, though, but they have one ovary with a number of cells and these lead to what the botanical reference books say are 2–4 seeds, although I have found as many as five. Some authorities say holly has berries, whilst others term them a multi-seeded drupe, which is confusing. Then there are yet others who say a berry must not have an endocarp >2mm thick. Perhaps the best term for these fruits is drupaceous. Another confusing example is ivy Hedera helix, which is referred to as a drupe by several sources but has two seeds in the fruits and a soft endocarp <2mm thick so would be a berry by that latter definition.
Oranges Citrus x sinensis abound at this time of year and anyone who has been to southern Europe at Christmas or New Year knows they ripen in winter there. This is one I photographed in my greenhouse this week. They will not stand more than a degree or two of frost so do not grow outside in England unless you have a very favoured frost-free, sunny spot. Oranges are formed from a single flower with several fused carpels and are a type of berry called a hesperidium, having a thick rind. They have no stony endocarp, which is fleshy and combined with the mesocarp. Seeds are in a tough testa. Other hesperidia include lemons, limes and grapefruit.
Cotoneasters are a very large group of shrubs with many hybrids and varieties. Several have escaped into the wild, a few being decidedly invasive. Some have winter berries like these in my photo, which you have probably seen. Most have red berries but some are yellow. In fact the fruit is strictly a pome. Pomes are fruits in which most of the fruit develops from the receptacle of the flower which then swells and becomes fleshy to enclose the true fruit within it. Apples are pomes as are pears and quinces, c.f. the French pomme.
Most of the hawthorn Crataegus monogyna fruits or haws have now disappeared from the hedges and woods in my area, eaten by birds, but the odd one can still be seen on the branches. The haw is another example of a pome and, like so many wild fruits, they are nutritious and attractive to foraging birds that then excrete the seeds and help the plants to spread. More than 300 insects are associated with hawthorns and the haws provide winter food for redwings, fieldfares and other thrushes. Several small mammals will eat them, too.
The red fruits (true berries) on the female plants of the common hedgerow and woodland climber black bryony Tamus (or Dioscorea) communis are going over now but can still be seen and brighten up a winter walk. This plant is a member of the same family as the yam, the Dioscoreaceae, and it has quite a large a tuber (rhizome). However, the plant, including the tuber and berries, is poisonous: presumably that is why the berries persist.
There are still a few rose Rosa canina agg. hips to be seen in our hedges, scrub and woods. This is another kind of fruit, a hypanthium that develops from the basal parts of the calyx, corolla and stamens. This surrounds the several ovaries of the flower. Seeds develop in the centre inside structures called achenes, one seed per achene. I confess that boys in our school used to make an itching powder from the central seed-containing parts of the hips. I do not recommend it as it is the devil to get rid of! Better to use the outer red skin as a good source of vitamin C.
Betts Ecology record fruits on our sites, whether they be berries, drupes, pomes or whatever. We are interested to know about any interesting or striking examples you may find.
Photos by the author © Betts Ecology
