Christmas plants: The traditions and science of festive flora

Move over Rudolph – it's not just animals that flourish at Christmas.

From colourful poinsettia to the spices used to make mulled drinks, plants are everywhere during the Christmas season. While some of these festive floral features have been winter staples for thousands of years, others are much more recent additions to our celebrations.

There are many examples of these plants in the Museum's collection, which stores over five million herbarium specimens from all over the world. In among the many specimens are also plants native to festive-sounding locations such as Christmas Island, or even collected on Christmas Day itself.

Here are several spectacular specimens that illustrate our changing culture over thousands of years.

Christmas trees – rooted in pagan celebrations

Having trees over the winter period is a tradition so old that it actually predates Christmas. Evergreen plants, whose leaves remain throughout the year, were used in pagan celebrations of the winter solstice as a reminder that life would return again in the coming seasons.

These traditions were later adopted by Christianity, with what we now know as Christmas trees having their roots in Protestant northern Europe in the fifteenth and sixteenth centuries. While it's not known exactly where the first Christmas tree was erected, Estonia, Latvia and Germany have all laid claim to this title based on different historical records.

The use of holly and ivy to make Christmas wreaths is also believed to have originated in the same region, and the traditions remained popular over the following centuries. As these countries' nobility increasingly married into families across Europe, the tradition of decorating trees began to spread.

Jacek Wajer, Curator of the Museum's General Herbarium, says, 'The first known Christmas tree in the UK was introduced by the German-born Queen Charlotte, the wife of King George III, in 1800. However, soldiers in the King's service, as well as merchants, may have brought the tradition across from the continent even earlier.'

One of King George III's descendants, Queen Victoria, made the custom of decorating trees popular among the general public around 40 years later when pictures of her Christmas celebrations were shared in magazines.

These trees would have been Picea abies, otherwise known as the Norway spruce, which is widespread across northern Europe and the UK. Around a century later, however, a new competitor emerged.

'The Norway spruce tends to lose its needles quite easily in centrally heated homes, so as this became more common, the Nordmann fir, or Abies nordmanniana, was introduced,' Jacek explains. 'As well as keeping its needles for longer, it also looks bushier and has less prickly foliage.'

Outside of Europe, a variety of other trees are a part of the festive period. Caribbean nations, for example, may use native plants such as the inkberry, Ilex glabra, for their Christmas trees, while some nations use species of juniper, a tree from the family of plants which includes those that gin is made from.

Mistletoe – a romantic parasite

Just like the Christmas tree, mistletoe was also originally used in pagan festivities over the winter period before being co-opted for Christian celebrations. There is no one mistletoe plant, as its name is given to a variety of different plant species with a parasitic lifestyle.

Some species of mistletoe can only grow on certain host plants, while others can target a range of different species, including other mistletoe. The species most associated with Christmas is Viscum album, or European mistletoe.

'Mistletoe can grow on a variety of plants, and most species are what are known as hemiparasites,' Jacek explains. 'This means that while they can carry out some processes like photosynthesis to produce food, they need to attach to a host to get water and a support to grow on.'

To do this, mistletoe has a variety of adaptations to help it take advantage of other plants. In particular, it develops a structure known as a haustorium that helps it to glue to the host's surface before penetrating its cells to absorb water and minerals.

Meanwhile, mistletoe's bright white seeds are an attractive food source to birds, who help to spread them from tree to tree. The sticky seeds get stuck to the bird's feathers when they are excreted, ensuring that the birds carry them to a new tree to wipe them off rather than dropping them mid-flight.

This sticky covering may have helped to inspire their association with fertility and romance, with the ancient Greeks describing the viscous white juice of their berries as 'oak sperm'. It wouldn't be until 1784, however, that the first reference of kissing under the mistletoe was made in England.

Around the same time, a mistletoe growing on the trunk of a Christmas tree was sent to the botanist Sir Joseph Banks, whose collections are held at the Museum. Combining two festive plants, it is possibly the Museum's most festive specimen.

Poinsettia – adding Mexican flair to Christmas

Poinsettia, Euphorbia pulcherrima, is also associated with ancient traditions, but not European ones. Instead, this member of the spurge family has its origins in Mexico.

'The Indigenous inhabitants of Central America used the poinsettia for religious purposes for centuries, as they are one of the few winter-flowering plants with decorative foliage that are native to the region,' Jacek explains. 'Christian settlers later repurposed the plant's religious meaning when they arrived.'

The plant's vibrantly red colour was compared by Christians to the blood of Christ and the chemicals responsible for it are so strong that the plant can retain its colour in herbarium specimens that are hundreds of years old.

These colours likely caught the eye of Joel Roberts Poinsett, an American diplomat who the plant is named after. He sent back samples of the plant to his homeland, where it slowly began to grow in popularity because of its 'flowers', which bloom around Christmas.

What may appear to be the flowers at first glance, however, are actually structures known as bracts. These are highly modified and brightly coloured leaves that have taken on an appearance similar to a bloom.

'The flowers themselves are tiny and reduced down to just the male and female parts with very few additional structures, so these leaves probably help to attract pollinators,' Jacek says.

'It's not entirely known what pollinates poinsettia, however, but it’s likely to be a species of wasp.'

Commercial poinsettias, however, don't rely on pollinators. They are produced by vegetative propagation, a process during which the plants are grafted together to pass on a parasite known as a phytoplasma which helps produce its branching form.

Though the science wasn't appreciated until the 1980s, the secret of grafting the plants together was discovered in the early twentieth century by the Ecke family, who produce around half of the world's poinsettias today.

The Eckes are partly responsible for the plant becoming a Christmas icon, as they heavily promoted their crops on a variety of American television shows over the festive period.

Aside from being a Christmas cash crop, poinsettia also contains a variety of useful chemicals which may have medical applications. Other poinsettia compounds, however, are irritants to the mouth and gut, so this plant should not be eaten by people or pets.

Star anise – a spice with a toxic doppelganger

In winter, spices such as cloves, cinnamon and nutmeg feature heavily in a variety of seasonal food and drink. Another frequently used spice is star anise, which can be used to make mulled wine.

Mulled wine, in one form or another, has been around for thousands of years. A recipe for spiced wine is the first in De Re Coquinaria, a collection of cooking instructions that dates back to the days of the Roman Empire!

Spiced wine is believed to have formed a part of the Roman celebration of the winter solstice, or Saturnalia, with the concept later being adapted to celebrate Christmas. As tastes changed over time, it became more like the mulled wine we know today.

Versions of mulled wine that use Chinese star anise, Illicium verum, are a French innovation. It's worth checking that you're using the right spice, however, as one of this plant's close relatives could turn Christmas celebrations into a murder mystery.

Krisztina Lohonya, a digitiser at the Museum, says, 'Japanese star anise [Illicium anisatum] is a very close relative of Chinese star anise used for incense, and visually they both look very similar.'

'Unlike its relative, however, Japanese star anise is highly toxic and should never be eaten. They're so visually similar that after they are harvested and dried it's almost impossible to tell them apart, except for through microscopic analysis.'

There are a few other Christmas plants you should be taking care around.

'It's not just this spice which is toxic when ingested,' Krisztina adds. 'Many festive plant species, such as holly, ivy and mistletoe, are all toxic to some degree. It's fascinating that humans love to use toxic plants for decoration and ornamentation.'

Coal – a plant of Christmas past

It may not sound like the most botanical of specimens, but coal more than deserves a place on a list of Christmas plants.

'In some ways, coal is a plant as well,' Jacek explains. 'Plants buried during the Permian Period were transformed into coal over hundreds of millions of years.'

Plants such as the seed ferns Glossopteris, which were buried over 250 million years ago, today make up significant amounts of the world's coal deposits after being subjected to heat and pressure under the ground.

Coal was used to fuel the Industrial Revolution and was widely used as a source of heat for homes from the late 1800s to the mid-1900s. Its ubiquity meant that it replaced stones as the traditional gift for bad children across Europe, given either on Christmas Day or on the Feast of St Nicholas, which is celebrated on 5 or 6 December.

Since then, scientists have come to recognise that coal is not just a bad gift for an individual, but the whole planet. Burning coal causes the production of greenhouse gases, which contribute to climate change. As a result, it is today being phased out of power generation by countries looking to move to a greener future.