Invasive Alien Species in Northern Ireland

Symphoricarpos albus, Snowberry

Symphoricarpos albus (L.) S.F.Blake
 
Introduction
The genus Symphoricarpos was first described in Great Britain by Dillenius in 1732 from William Sherard's garden at Eltham. Symphoricarpos albus var. laevigatus was introduced into cultivation in 1817. It became a very popular hedging and shrubbery plant in Victorian and Edwardian gardens and estates, but because of its extremely invasive habit, it has now fallen out of popularity; it is, however, still used occasionally for hedging or ornament. Several other taxa are grown but so far do not appear to have had any impact in the wild in Ireland.
 
Description
A deciduous shrub of older gardens, reaching two metres in height, much given to suckering vigorously and forming thickets. Whippy, bright brown, shiny branches bear mid-green leaves up to c. 7cm long, which are usually rounded but occasionally lobed. Clusters of tiny bright pink, bell-like flowers, c.6mm long, appear at the ends of the branches from spring right through the summer, and are followed from late summer by round, waxy-looking, white berries which are up to 1.5cm in diameter.
 
Country of origin
The species is native to North America from the Atlantic to the Pacific. In the Pacific region it is represented by var. laevigatus – this is the variety normally seen in cultivation in Great Britain and Ireland.
 
Current distribution
There is little information on its occurrence outside its native range, except for its cultivation as a garden plant.
 
Location in Ireland
Very common in Ireland, having spread from its original plantings to surrounding areas, often seen in field hedges and older or abandoned gardens.
 
Life cycle
A flowering plant producing many fruits, each with two seeds. It also produces numerous suckers.
 
Wildlife and habitat impacts
Originally planted in open woodland for game covert, it has adapted to a wide range of open and semi-open habitats.
Its vigorous suckering habit causes it to spread widely from its original planting; it then produces dense thickets which outcompete other less vigorous plants.
The leaves are food for caterpillars of death's head hawkmoths.
Fruits can be eaten whole by larger birds such as blackbirds; other smaller bird species, especially finches, will remove the pulp to gain access to the seeds.
Thickets will provide good cover for smaller mammals.
 
Human impacts
The plant has no economic value but its invasive habit has implications for eradication programmes. It is often stated that the berries might be poisonous to humans, but as the main compound isolated is a weak saponin it is likely that it is not very toxic, except if eaten in very large quantities.
However, although believed to be poisonous, it is not clear that this is so – in North America it was extensively used by many native peoples as a medication for a variety of ailments, ranging from external conditions such as skin disorders and injuries, to a host of internal ailments such as fevers, venereal disease and kidney disorders. It is now almost never used in herbal medication.
 
Key vectors
Its main method of spread is by means of its vigorous suckering habit; it does not appear to propagate much by seed. It can be spread from garden waste containing plant fragments.
 
What you can do as an individual
Destroy any prunings by incineration, or thorough shredding into small fragments. Do not discard into the countryside.
 
Advice to specific groups relevant to this species
None relevant.
 
Management measures
It may be eradicated by spraying with a strong glyphosate-based herbicide, which must be applied when the plant is in full leaf. Several applications may be required.
 
Management groups
Land managers and staff should ensure that this plant does not escape into surrounding countryside.
 
Further information
Links
Plant for a Future
The Science and Plants for Schools Web site
Borealforest.org
 
Literature
Bean, W. J. (1980). Trees and Shrubs Hardy in the British Isles Vol. IV, Eighth Edition. John Murray, London.
 
Text written by:
Catherine Tyrie, Curator, Botany, Ulster Museum