groundsel bush

Baccharis halimifolia
habit (Photo: Sheldon Navie)
habit of female plant in flower (Photo: Sheldon Navie)
habit of male plant in flower (Photo: Sheldon Navie)
lower leaves (Photo: Sheldon Navie)
upper leaves and old male flower-heads (Photo: Sheldon Navie)
young female flower-heads (Photo: Sheldon Navie)
old female flower-heads (Photo: Sheldon Navie)
masss of seeds with fluffy hairs (Photo: Sheldon Navie)
young plant (Photo: Sheldon Navie)
gall caused by the gall-fly biocontrol agent Rhopalomyia californica (Photo: Sheldon Navie)
damage caused by the plume moth biocontrol agent Oidaematophorus balanotes (Photo: Sheldon Navie)
Shrub
Alternate
Simple
White
Cream
Green

An upright bushy shrub (1-3 m tall) with much-branched stems that become woody with ageits waxy leaves (2.5-7.0 cm long and 1-4 cm wide) have coarsely toothed margins. It produces separate male and female flower-heads on separate plants. The male flower-heads are cream to yellowish, while the female flower-heads are white and have a fluffy appearance its straw-coloured or brown seeds (about 3 mm long) and are topped with a silky tuft of long white hairs (up to 12 mm long).

Common names 
Also known as: groundsel bush, consumption weed, groundsel, groundsel tree, Sea Island myrtle, tree groundsel, waterbrush,
Family 
Asteraceae
Deciduous 
No
Flowering time 
Autumn
Native/Exotic 
Exotic
Origin 
Native to eastern USA and the Caribbean.
Notifiable 
No
State declaration 
Category 3 - Must not be distributed or disposed. This means it must not be released into the environment unless the distribution or disposal is authorised in a regulation or under a permit.
Council declaration 
As per State Declaration
Known distribution 

A relatively widely naturalised species that is mostly found in eastern Australia. It is very common in south-eastern Queensland and north-eastern New South Wales, and is also present in other parts of these states (i.e. in central Queensland and in the coastal districts of central New South Wales). It was possibly also sparingly naturalised near Busselton in south-western Western Australia, but is no longer thought to be present in Western Australia. Naturalised overseas in Europe and New Zealand.

Habitat 

A weed of open woodlands, forests, waste areas, disturbed sites, coastal canals, swampy areas, estuaries, mangrove wetlands, pastures, forestry plantations, orchards, plantation crops, irrigation channels, creek banks (i.e. riparian areas), parks, gardens, roadsides and urban bushland. It is mainly present in warmer temperate and sub-tropical climates.

Habit 

An upright (i.e. erect) and bushy shrub or small tree with many upward growing (i.e. ascending) branches. It usually grows 1-3 m tall, but occasionally reaches up to 7 m in height.

Impact and control methods 

Groundsel bush (Baccharis halimifolia) is regarded as a significant environmental weed in Queensland and New South Wales. During a recent study it was listed as the second most important invasive plant species in south-eastern Queensland. It also rated highly in a survey of the most important environmental weeds of the New South Wales North Coast region. It is actively managed by community groups in Queensland and is also currently listed as a priority environmental weed in two Natural Resource Management regions.This species is of most concern in sub-tropical melaleuca wetlands, where it can form a dense understorey that suppresses the growth of native sedges and interferes with the natural ecosystem. It can also become abundant in native vegetation along watercourses and in coastal woodlands and forests. Conservation areas are also under threat from invasion by this species, and it has invaded several reserves in Queensland (e.g. Noosa National Park, Maroochy River Conservation Park and Pimpama River Conservation Area) and New South Wales (e.g. Ballina Nature Reserve, Wooyung Nature Reserve and Cullendulla National Park).

Stem and leaves 

The much-branched stems are hairless (i.e. glabrous), finely ribbed lengthwise (i.e. striate), and green when young. They turn brown, become woody, and eventually develop a deeply fissured bark as they mature. The alternately arranged leaves are loosely diamond-shaped (i.e. rhomboid) to egg-shaped in outline (i.e. ovate) and have coarsely toothed (i.e. crenate) margins. These leaves (2.5-7 cm long and 1-4 cm wide) are borne on stalks (i.e. petioles) up to 15 mm long and have a waxy texture. They are hairless (i.e. glabrous) and can have either pointed or rounded tips (i.e. acute or obtuse apices). Leaves tend to be light green when young and turn a dull green colour as they mature, and the upper leaves tend to be smaller and less toothed or even have entire margins.

Flowers and fruits 

Separate male and female (i.e. unisexual) flower-heads (i.e. capitula) are borne on separate plants (i.e. this species is dioecious). The male (i.e. staminate) flower-heads (about 3 mm across) are cream to yellowish in colour, while the female (i.e. pistillate) flower-heads (3-5 mm across) are white and tend to mature after the male flower-heads. These flower-heads (i.e. capitula) not not have any 'petals' (i.e. ray florets) and their bases are enclosed in a few layers (i.e. involucre) of green bracts. Both types of flower-heads are grouped in branched clusters at the tips of the stems (i.e. in terminal panicles). Flowering occurs mainly during autumn. The 'seeds' (i.e. achenes) are straw-coloured to brown in colour and hairless (i.e. glabrous). These 'seeds' (1.1-1.7 mm long) have 8-10 lengthwise (i.e. longitudinal) ribs and are topped with a silky tuft (i.e. pappus) of long white hairs (6-12 mm long).

Reproduction and dispersal 

The female plants produce large numbers of light fluffy seeds. These seeds are blown large distances by the wind and float on water. They may also be dispersed by animals, vehicles, machinery, and in contaminated agricultural produce (e.g. fodder).