Species of the month – the butterbur

Have you ever wondered about the giant rhubarb-like plants that loom up in huge swathes? The butterbur is our species of the month.

Butterbur (Petasites hybridus) in flower. ©Lorne Gill/SNH

Butterbur (Petasites hybridus) in flower.

The name butterbur allegedly comes from a practice of wrapping butter in the large leaves of the plant to keep the butter clean and to help it last. Butterbur certainly has large leaves, reaching 90 cm across.  They appear in about March to April, around about the same time the plant produces pale pink to purplish spikes of flowers.  The leaves resemble rhubarb leaves, perhaps slightly more heart-shaped.  Although small when the plants are flowering, they later become so big that it is hard to believe they belong in Scotland.  They are however the largest leaves of any native British plant.  The scientific name for the butterbur genus Petasites originates from the Greek word petasos the name for a felt, leather or straw hat with a wide brim and worn by farmers in ancient Greece.  These leaves do indeed feel “felty” and would be large enough for a sun hat.

White butterbur (Petasites albus) growing on a road verge in Perthshire. ©Lorne Gill/SNH

White butterbur (Petasites albus) growing on a road verge in Perthshire.

One of the most fascinating things about the butterbur is the odd distribution of the male and female plants.  For some reason male plants have a wider distribution, with almost all butterbur in the south of England being male.  How could that be?  The answer could be that male plants produce both nectar and pollen at a time of year when few native species are flowering.  There is a suggestion that in the past the male plants were deliberately moved about as a source of food for honey bees during the early spring.  We might buy our sugar from shops, but in the past honey was highly valued and used for sweetening so planting butterbur to help the bees is a plausible explanation.

Distribution anomalies also occur abroad.  In Finland the plants appear to be predominantly male, possibly because they were planted both for their ornamental value and for the benefit of bees.  However the rhizomes spread, and the plant has become invasive in some areas of Finland where it is a non-native.

The white butterbur (Petasites albus) is native to mainland Europe and mountainous south-west Asia, but has been present in the UK since 1683 when it was imported for ornamental purposes.  White butterbur seems to like the climate of north-east Scotland and is certainly widespread along water courses near Inverness.  White butterbur leaves have a white felt underneath and are difficult to separate from our native butterbur, but they don’t reach the same size.

White Butterbur (Petasites albus) a non-native flowering plant found growing at Quarrymill woodland park near Perth ©Lorne Gill/SNH

White Butterbur (Petasites albus) a non-native flowering plant found growing at Quarrymill woodland park near Perth

White butterbur does not appear to have spread into many new sites since 2000, so can it be considered invasive?  Probably so.  White butterbur can become dominant at ground level, out-competing native woodland species.  It has the capacity to spread all over the place by underground rhizomes and can survive in dark woodland.

Even more ornamental, verging upon the exotic, is the giant butterbur (Petasites japonicus).  It has spectacularly large leaves, up to a meter across, which make the plant look like an escape from a winter garden.  Giant butterbur was introduced from Japan on account of those amazing leaves, giving rise to its alternative name Japanese butterbur.  Giant butterbur could be confused with our native species, but the leaves have a rounder, less wavy margin with lots of small teeth of similar size.  In the UK giant butterbur seems to be more widespread in the south, but in Scotland it can survive quite far north, e.g. beside the River Nairn, where it grows head and shoulders above a carpet of white butterbur.  Until now giant butterbur has not spread extensively, but since our climate appears to be changing, it is definitely one to keep an eye on.

You may encounter a fourth species of butterbur, the winter heliotrope (Petasites fragrans), particularly if you live in the warmer parts of Scotland.  Introduced from North Africa, only the male flowers are found in the UK.  The vanilla-scented flowers appear in the middle of winter, earlier than our native butterbur.  The flowers are a similar pale pink to purple to native butterbur, but with smaller leaves, up to about 30 cm across, and heart-shaped, but with the bottom of the heart rounded rather than coming to a point.  Although an African species might seem  an unlikely plant to survive the Scottish climate, records have come from as far north as Shetland, nicely illustrating the importance of recorded non-native species if you happen to spot them “in the wild”.

If you spot any butterbur species in the wild, consider sending details to BSBI which collates plant records in the UK.

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