Short description of Petasites albus, White Butterbur

It is a rhizomatous perennial herb which dies back in the winter. Leaves are all basal, up to 30 cm in diameter, broadly rounded, shallowly lobed and often toothed, with whitish lower surfaces. Stout flower stems up to 30 cm appear before leaves in late winter or early spring bearing many pure white tubular flowers. The female plant is much less common than the male but it may produce dandelion-like seeds with long white hairs.

Impact summary: Petasites albus, White Butterbur

By forming extensive pure patches it out-competes and degrades native vegetation and can be locally damaging to sensitive sites.

Habitat summary: Petasites albus, White Butterbur

Typically damp clayey ground along watercourses, road-verges, waysides and in woodland.

Overview table

Environment	Terrestrial
Species status	Non-Native
Native range	Europe, Asia-Temperate, Northern Europe, Middle Europe
Functional type	Land plant
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	v.c.64 (Storthes Hall)
Date of first record	1843

Origin

It is a native of mountainous parts of Europe and the Caucasus.

First Record

It was known from the wild by at least 1843 in West Yorkshire.

Pathway and Method

It was first imported as a garden ornamental in 1683 and continues to be promoted as an attractive perennial for damp places. The female plant is much less commonly planted than the male. It escapes into the wild as garden cast-outs or deliberate plantings in semi-natural situations and is able to regenerate rapidly from fragments of rhizome. It can spread along stream and river corridors by means of rhizome fragments carried by the water.

Species Status

It is naturalised throughout GB. By 1999 it had been recorded in 345 10km grid squares, with approximately two thirds of the populations recorded after 1986. After 2000 it does not appear to have spread into many new sites. It has also been introduced to Belgium but is not regarded as established there.

Dispersal Mechanisms

Dispersal of naturalised plants appears to occur mainly or exclusively by vegetative means. It spreads via an extensive rhizome network and pieces of rhizome have the potential to form new colonies if moved away from the parent plant. The dispersal mechanisms in GB are poorly documented but it is known that plants growing along watercourses can spread via fragments of rhizome detached and carried downstream. Seeds (if produced at all) are wind-dispersed.

Reproduction

Plants are dioecious, consisting of separate male and female plants which are not self-fertile. In GB plants flower as early as February and the inflorescences are visited by various insects. If pollinated, female plants bear dandelion-like cylindrical seeds with a tuft of long white hairs. As the vast majority of naturalised populations in GB consist entirely of male plants the extent of sexual reproduction is unclear.

Known Predators/Herbivores

None known.

Resistant Stages

Rhizomes are tough and difficult to eradicate once well-established. The viability of any seed produced by naturalised plants is unknown.

Habitat Occupied in GB

It is naturalised in shaded or open places in rough ground, waysides, woods, road verges and on the banks of rivers and streams.

It is much more widespread in northern parts of GB than the south, with a concentration of sites in lowland north-eastern Scotland. It is absent from south-west England and Ireland.

Environmental Impact

It can form pure patches many metres across, suppressing native vegetation in sites of ecological importance and reducing natural diversity. It appears to be invasive in disturbed flood-prone ground in Scotland.

Health and Social Impact

Large patches of this plant in nature reserves or other scenic spots may be a minor visual annoyance for some people, but others may value its early flowers.  

Economic Impact

There is no information about the economic impacts of White Butterbur but its removal is likely to incur significant costs to those charged with maintaining biodiversity in sensitive sites.

Identification

Sell, P. & Murrell, G. (2006) Flora of Great Britain and Ireland: Volume 4: Campanulaceae to Asteraceae, Cambridge University Press.

Stace, C.A. (2010) New flora of the British Isles, Third Edition, Cambridge University Press, Cambridge.

Biology, ecology, spread, vectors

Horwood, A.R. (1919) British Wild Flowers - In Their Natural Haunts, The Gresham Publishing Company.

Preston, C.D., Pearman, D.A. & Dines, T.D. (2002) New Atlas of the British and Irish Flora, Oxford University Press, Oxford.

Distribution map from DAISIE European Invasive Alien Species Gateway: www.europe-aliens.org

Distribution map from the NBN Gateway: www.searchnbn.net/searchengine/search.jsp?tab=1&pg=1&searchTerm=Petasites+albus

Management and impact

Parrott, J. (2008) Non-native plants in the Glenurquhart Catchment: survey and management recommendations, A report for Scottish Natural Heritage.

General

General background information from Wikipedia: www.en.wikipedia.org