Short description of Baccharis halimifolia, Tree Groundsel

A dioecious, salt-tolerant, fast-growing shrub that is grown for ornament or hedging in coastal areas. Introduced to the UK from North America in the 1920s and known to be invasive in coastal habitats in Europe and Australia.

Impact summary: Baccharis halimifolia, Tree Groundsel

Invasive in coastal habitats where it outcompetes native species and alters ecosystem properties. Its leaves are toxic to livestock and its pollen and pappus are allergenic to humans. It is difficult and expensive to control or eradicate.

Habitat summary: Baccharis halimifolia, Tree Groundsel

In its native range, Baccharis halimifolia occurs in tidal wetlands and upper saltmarshes and disturbed communities inland including open woods, abandoned fields and deserts. It has invaded coastal habitats in Europe and Australia as well as coastal woodlands, and pastures and waste-ground further inland.

Overview table

Environment	Terrestrial
Species status	Non-Native
Native range
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.11
Date of first record	1924

Origin

An ornamental or hedging plant introduced from North America.

First Record

Baccharis halimiifolia was introduced into cultivation in Britain in 1683. It was first recorded in the wild at Mudeford Quay in 1924.

Pathway and Method

Planted for ornament in gardens or as a hedging plant in coastal areas, because of its attractive scented flowers, hardiness, freedom from disease, autumn flowering and resistance to salt spray. It does not appear to be spreading at its sole locality in the UK.

Species Status

Baccharis halimifolia has been recorded at three coastal sites in the UK: Mudeford Quay, South Hampshire (1924 onwards); Hamworthy, Dorset (1958); and Machrihanish Links, Kintyre (1988). It only survives at Mudeford where it was probably planted and was first recorded in 1924. The population is very small and does not appear to invasive or spreading (Jones, 2017). Invasive in parts of Europe and Australia as well as parts of its native range (e.g. Florida).

Dispersal Mechanisms

Baccharis halimifoliaproduces vast quantities of seed. The seeds are small and firmly attached to a pappus which aids wind-dispersal.

Reproduction

Baccharis halimifolia is a fast-growing shrub that appears to regenerate almost exclusively by seed. It is a dioecious species and therefore male and female plants are required for seed production. Seed production increases in response to higher light levels but declines with age.

Known Predators/Herbivores

The larvae and adults of a range of beetles and moths are known to defoliate leaves of Baccharis halimifolia in its native range. A rust (Puccinia evadens) has also been reported to cause defoliation and stem die-back. Many phytophagous insects have been tested as biological control agents in Australia and the USA but none have so far been shown to effectively control B. halimifolia.

Resistant Stages

Baccharis halimifolia can survive periodic flooding and droughts and is tolerant of shade, salt spray and low soil fertility. It can quickly regrow once cut back or burnt.

Habitat Occupied in GB

At Mudeford Baccharis halimifolia grows on compacted sandy soils close to the sea (Jones, 2017).

Currently surviving (but not spreading) at one coastal site in South Hampshire where it was introduced in the 1920s.

Environmental Impact

Baccharis halimifolia has the capacity to form a dense understorey in coastal wetlands, saltmarshes, and woodlands, suppressing native species and altering habitat composition and ecosystem properties.

Health and Social Impact

The wind-dispersed seeds and pollen can be a nuisance in urban areas where they establish in gardens, coat surfaces and cause allergenic reactions (e.g. hay-fever).

Economic Impact

Baccharis halimifolia can become a weed in agricultural pastures where it competes with forage species and is toxic to livestock. Its control or eradication from agricultural habitats can be very time-consuming and expensive.

Identification

Poland, J. & Clement, E. 2010. Vegetative Key. Botanical Society of Britain and Ireland, London.

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

Stace, C.E. 2010. New Flora of the British Isles. Third Edition. Cambridge University Press, Cambridge.

Biology, ecology, spread, vectors

CABI 2015. Invasive Species Compendium. Baccharis halimifolia. http://www.cabi.org/isc/datasheet/8164.

Caño, L., Campos, J.A., García-Magro, D. & Herrera, M. 2013. Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe. Biological Invasions 15, 1183-1188.

USDA 2017. USDA Plant Profile. Baccharis halimifolia. https://plants.usda.gov/core/profile?symbol=BACCH.

Management and impact

CABI 2015. Invasive Species Compendium. Baccharis halimifolia. http://www.cabi.org/isc/datasheet/8164.

USDA 2017. USDA Plant Profile. Baccharis halimifolia. https://plants.usda.gov/core/profile?symbol=BACCH.

General

David, J. 2017. Baccharis halimifolia in BSBI News 134: 48-50. BSBI News 135, 77-78.

Jones, L. 2017. Baccharis halimifolia (Tree Groundsel) persists at Little Haven, South Hampshire (v.c.11). BSBI News 134, 48-50.