Jan

Petasites albus – January 13th 2025 – White Butterbur

Many readers will be familiar with butterburs. There are four species in Britain – the most common is the only native one, P. hybridus. All four are discussed in Richard Milne’s blog from March 2021. The name Petasites comes from the Greek word for an ancient type of broad-rimmed hat πέτασος petasos; the plant’s broad leaves do resemble this headgear although the leaves are usually not quite as large as the hat. The English name butterbur comes from the plant’s medieval use to wrap butter. The native P. hybridus was well known to John Gerard in the 16th Century – it was a widely used medicinal plant as well as being useful as wrapping-paper. He says: it “cureth all naughty filthy ulcers” .

How the genus got its name. The leaves resemble a petasos, as worn by ancient Greeks. The left-hand image is P. hybridus from Gerard’s 1597 Herbal. The centre image is Hermes (attribution: the Louvre Museum), the right-hand image is from a coin used in ancient Macedonia 400 BC. Public domain, via Wikimedia Commons.

This week we focus attention on an alien butterbur that has made its headquarters in the north-east of Scotland, especially around Inverness. Petasites albus likes its new home so well that in some situations it is considered invasive.

Petasites albus is native in mountainous regions of Europe and the Caucasus. According to the BSBI’s Atlas 2020, it was introduced to Britain by 1683, and found in the wild by 1840 in Wimbotsham, West Norfolk. Probably it was appreciated as an ornamental plant in the grounds of the large estates, and ‘escaped’ to the wild because eventually its tendency to spread became a nuisance and it was thrown out. Its build-up in the north-east of Scotland appears to have occurred in the 1950s.

As with all butterburs and their cousin the coltsfoot, the plants produce a flowering spike well before the main leaves appear. Chris Jeffree’s picture of emerging flowers (below) is one of my favourite plant images. The flowers are white and clustered, the stem-leaves are pale green; the scene resembles a crowd of kids running downhill.

These shoots arise from rhizomes, and careful inspection of the scene reveals a degree of linearity caused by shoots emerging at intervals along the rhizome.

Flowering population, 22nd February at Dawyck in the Scottish Borders. Image: Chris Jeffree.

The species is one of the first to flower, and you may see the flowers any time from mid-February. It occurs near rivers, in damp areas in woods and along roadsides. It always appears as a colony, usually several metres across, as a result of its rhizomatous means of reproduction. The flowers produce nectar and they are visited by insects, but the species is dioecious and (nearly all?) plants in Britain are male. Therefore, there is no prospect of sexual union and dispersal depends on fragments of rhizomes which may be carried away in flooding rivers, perhaps spread by birds and even (in the case of roadside populations) the tyres of motor cars. More work is needed to establish the modes of dispersal.

Petasites albus on the bank of a small stream, Dawyck ,28th February. Image: Chris Jeffree.

The flowering period is soon over as summer approaches; the flowers whither and the main leaves appear, growing to 30 cm across, about the same size as those of the native P. hybridus but much smaller than the almost-1-metre leaves of Giant Butterbur P. japonica. The leaves will actively photosynthesise for several months and recharge the rhizome system ready for next year. The carbohydrate store in Petasites rhizomes and in other members of this Family is a fructan (inulin, a polymer of fructose, not digested by many people’s enzyme system and the reason why Jerusalem artichokes give many of us acute indigestion) rather than starch (an easily digested polymer of glucose).

Post-flowering population showing emergence of leaves, 7th April. Image Chris Jeffree.

The genus Petasites belongs to the Asteracea, although its flowers are not daisy-like. Most of the Asteracea have tubular disk florets and ray florets, as in daisies and sunflowers; but in the male flowers of P. albus there is a single floret representing the disk and the several ray florets are sterile, well-developed to attract the attention of flying insects. The single tube florets have one club-shaped stamen, bearing pollen. In close-up images the flowers are truly beautiful to behold.

Flowers of P. albus. Images: Chris Jeffree

.It may come as a surprise to see that P. albus has a possible African heritage, and also that it is recorded in India, yet it is native as far north as Scandinavia. Its distribution contrasts strongly with the Winter Butterbur Petasites pyrenaicus (which, by the way, is flowering now).

Left: P. albus; right P. pyrenaicus (formerly P. fragrans). Colour code: green for native range, red for extinct, purple for ‘introduced’. From Kew’s Plants of the World Online.

In Britain there is an interesting contrast in distributions of Petasites albus and P. pyrenaicus. Their distributions are almost inverse: where one is highly recorded the other is not. It is of course too early to talk about the possibility that one out-competes the other in the north-east and south-west. It is too early to tell.

Left: P. albus; right P. pyrenaicus (formerly P. fragrans). From BSBI/maps.

Kulinowski et al. (2022) have reviewed the whole genus from a pharmacological perspective. They list ancient and modern uses which include the treatment of migraine, asthma, allergic rhinitis, cough, hypertension, gastric ulcers and dysmenorrhea. They list the many compounds found in the tissues of Petasites and highlight a sesquiterpene named after the genus, called petasin. There are however, some seriously toxic compounds and so development of acceptable products from the raw material has depended on development of subtle methods to separate the ‘good’ from the ‘bad’.

Attribution

The image appearing at the top of this article is by Chris Jeffree. It shows P. albus growing by the roadside near the Bush Estate, Midlothian, among broken glass. It demonstrates a wide tolerance of disturbed man-made habitats. P. hybridus and P. pyrenaicus are also found by roadsides.

Articles consulted

Kubov M (2022) Effect of Selected Meteorological Variables on Full Flowering of Some Forest Herbs in the Western Carpathians. Atmosphere13, 195. https://doi.org/10.3390/atmos13020195

Łukasz K et al (2022) A review on the ethnobotany, phytochemistry, pharmacology and toxicology of butterbur species (Petasites L.), Journal of Ethnopharmacology, 293, 115263

https://doi.org/10.1016/j.jep.2022.115263.

https://www.nonnativespecies.org/non-native-species/information-portal/view/2606

https://www.invasivespecies.scot/white-butterbur

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