Groundsel Bush

Baccharis halimifolia L.

Family: Asteraceae

Names:

Baccharis is from the Greek word bakkaris meaning an oil producing plant or a plant with a fragrant root.
Halimifolia is from the Greek alimos meaning belonging to the sea and the Latin folium meaning leaf. Sea leaf alludes to the salt like waxy powder that is often seen on the leaves.
Groundsel refers to the groundsel like flowering heads.

Other Names:

Groundsel Baccharis (USA)
Groundsel Tree

Summary:

A bushy, shrub or small tree, up to 7 metres high often growing in low lying areas near the coast. Separate male and female plants. The white hairs on seeds on female plants give them a cobwebby or fluffy appearance when in fruit in autumn.

Description:

Cotyledons:

Two.

First leaves:

Leaves:

Alternate. Pale green or dull, waxy to touch.
Stipules -
Petiole - Yes.
Blade - 25-50 mm long x 12-25 mm wide, wedge shaped, with a few large teeth near the tip, waxy. Leaves near the ends of branches often tapered at both ends and without obvious teeth.

Stems:

Initially green becoming brown with age. Conspicuous lengthwise markings. Erect, densely branched above, 1000-2500 mm tall usually but occasionally becoming a small tree up to 7000 mm tall.
Bark of mature plants deeply fissured.

Flower head:

Male - yellow to cream in globular heads about 6 mm diameter.
Female - white in heads clustered at the ends of branches.
Many male and female flowers in clusters on separate plants.

Flowers:

Female flowers mature later than male flowers.
Female - white
Ovary -
Florets -
Stamens -
Anthers -

Fruit:

Seeds:

Brown to straw colour, ~3 mm long, ribbed. Pappus of silky hairs up to 12 mm long on top.

Roots:

Deep branching taproot with many fibrous laterals in the top soil.

Key Characters:

Biology:

Life cycle:

Seeds germinate whenever moisture is available with a flush in late winter to spring. The seedling growth rate is slow and root growth exceeds shoot growth initially. In summer the growth rates increases and plants reach a height of about a metre by autumn before growth slows again over winter. It is ever green in warmer areas but may be semi deciduous and somewhat dormant over winter in cooler areas. It resumes rapid growth in summer and flowers in its second autumn. Male plants start flowering about 2 weeks before the females and continue for another few weeks after the female flowering has finished. The plant lives for several years.

Physiology:

Tolerant to saline conditions and salt spray.
Tolerates a wide range of pH from at least 3.8 to 8.2.
It does not tolerate low phosphorous levels but is tolerant of nitrogen deficiency for extended periods.

Reproduction:

By seed.
Separate male and female plants.

Flowering times:

Autumn.

Seed Biology and Germination:

The seed has little dormancy and germinates when moistened. At room temperature it only remains viable for around 14 months but it may remain viable for longer periods when buried.
Germination is stimulated by exposure to light, stratification by low (50C) but not freezing temperatures, and alternating day/night temperatures of 20/150C.

Vegetative Propagules:

None.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

It is spread as seeds by wind and water assisted by the hairy pappus which remains attached to the seed for several days after release. In a 16 kph wind most seed falls within 6 metres of the parent plant with odd seeds travelling up to 150 metres. In gusty conditions the seed is lifted vertically and may travel much greater distances. Water, agricultural produce, vehicles, sand and gravel used for road making carries seed long distances.
Large amounts of seed are produced with plants 2-3 metres tall producing up to 1 million seeds. Most seed is produced in open areas but it still produces some seed under dense shade.
It is a pioneer plant and readily invades areas disturbed by machinery, fire or flood.
It currently has not reached the limits of its environmental range and is expected to invade new areas over the next few decades and become a serious environmental weed.

Origin and History:

Native to Central and Northern America ( Atlantic and Gulf coasts) and the West Indies.
After introduction to France and USSR during World War II, it has become an important weed along the coast of France, Spain, Biscay and the Black Sea.
Introduced to Queensland as an ornamental in the late 1800's and was naturalised between Tin Can Bay and Tweed River by 1888 and remained relatively restricted to swampy areas for the next 50 years. By 1930 it was becoming a problem on drier soils.
In 1941 it had naturalised in NSW at Terranora.
It now spreads from Smoky Bay in NSW to nearly Gladstone in Queensland. The worst infestation of about 13,000 ha is 50-150 Km north of Brisbane in the Maroochy Shire.

Distribution:

NSW, QLD.
Widespread on the central and north coast of NSW and south eastern QLD.
Recorded from Busselton in WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Disturbed areas, low lying coastal swamps, semi tidal areas, Irrigation channels and canals.
Often invades areas where the understorey is removed regularly by fire or floods.

Climate:

Sub tropical and humid warm temperate areas.

Soil:

Grows on a wide range of soil types.

Plant Associations:

Readily invades disturbed Paperbark Teatree (Melaleuca quinquenervia) swamps and coastal Eucalyptus forests.
Pasture.

Significance:

Beneficial:

Honey plant.

Detrimental:

Weed of low lying pastures and disturbed sites.
Possibly toxic.
Suspected cause of hay fever.
Often forms dense impenetrable thickets, restricting the movement of stock, vehicles and displacing pasture species.
Little feed value.

Toxicity:

Reported to be toxic to stock in the USA but and is suspected to be toxic to sheep and cattle in Australia. It was toxic to chickens in feeding tests.
The toxic principal appears to be a glycosidal saponin.

Symptoms:

Treatment:

Legislation:

Noxious weed of New South Wales, Queensland and the Northern Territory.

Management and Control:

Cultivation provides effective control providing the area is replanted to vigorous pasture or native species. Kikuyu provides sufficient competition to prevent new invasions.
Blade plough or use tandem weighted offset discs. Leave for 6-8 weeks then burn. Repeat the cultivation at the break of the season and then harrow in a suitable grass plus legume pasture mix. Fertilise with superphosphate and molybdenum annually. Graze lightly in the first year. If patches of Groundsel Bush appear then spray with 2,4-D amine.
On areas too steep for cultivation, glyphosate applied through a blanket wiper or wick applicator is effective.
Spraying with Tordon® 75-D, glyphosate, 2,4-D or dicamba plus MCPA is effective on smaller bushes when they are actively growing. Larger bushes should be slashed then herbicides applied to the regrowth when it is 500 mm tall and actively growing. Small trees may be treated by basal bark or cut stump methods using Access, Grazon or Garlon.
Aerial applications of Graslan are used in Queensland.

Thresholds:

Eradication strategies:

Grub individual plants or cut their roots well below the ground surface.

Herbicide resistance:

None reported.

Biological Control:

5 species of introduced insects have established on Groundsel Bush and are providing encouraging degrees of control.

Related plants:

None.

Plants of similar appearance:

Epilobium species have a similar fluffy appearance at seeding but is much smaller and has pods.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P85. Photograph.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia).

Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #120.1

Parsons, W.T. and Cuthbertson, E.G. (1992) Noxious weeds of Australia. (Inkata Press, Melbourne). P256-259. Photographs.