APC (2021). Australian Plant Census. Council of Heads of Australasian Herbaria (CHAH). Available at: https://biodiversity.org.au/nsl/services/apc. [accessed 18/02/2021].
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Galvanised Burr (Sclerolaena birchii) is an erect, dense, rounded, short-lived perennial shrub which grows to about 1 m high and wide, with many plants dying within two years, and few plants surviving for more than four years. It has a robust taproot up to 80 cm in length with superficial secondary roots. The branches are grey-green in colour and covered with dense white woolly hairs. The leaves are obovate (egg-shaped in outline with the widest part nearer the tip of the leaflet) to elliptic (longer than wide, with widest point in the middle and equally narrow at both ends) shape, usually 7–15 mm long but may reach 25 mm in length, they are grey to blue-green and covered with short white hairs. The leaf stalk is absent or very short and the margins are entire.
The flowers are small inconspicuous, found in the leaf axils and have spines attached to the perianth (petal-like structure), white.
The fruit is hard and woolly 1.5-2–5 mm long and wide. It has 5 divergent spines (occasionally 4), 3 on one side 2 on the other. Each burr contains one seed (Cunningham et al. 1992; Walsh & Entwisle 1996; Parson & Cuthbertson 2001; Harden 2007), and the seed is retained until hard coat is broken down.
For further information and assistance with identification of Galvanised Burr contact the herbarium in your state or territory.
Galvanised Burr grows in sandy soils in subtropical, warm-temperate and semi arid areas of eastern Australia within the 300–500 mm rain belt. (Parsons & Cuthbertson 2001).
Other species of Sclerolaena may appear similar to Galvanised Burr, but the hairy fruit with 5 long, straight spines and the obovate leaves distinguish it from other species (Harden 2007).
Galvanised Burr (Sclerolaena birchii) is a pioneer species on soil denuded of vegetation by drought, overgrazing or erosion. It quickly colonizes bare overgrazed and drought effected pasture when rainfall occurs. (Everist et al. 1976). Light infestations can perform a useful function as a soil stabilizer acting as a trap for seed and other debris and protecting seedlings (Everist et al. 1976). Although the plant population increases rapidly after rain it slowly declines as it is affected by water stress. (Parsons & Cuthbertson 2001).
Agriculture: It competes with useful pasture species and in dense infestations the spines may hinder the movement of stock (Parsons & Cuthbertson 2001). Very heavy infestations of Galvanised Burr are reported to reduce stock-carrying capacity (Everist et al. 1976). Mature plants are not usually grazed because of the spines on the burrs along its stems (Auld 1981). However, seedlings and shoot tips can be a useful fodder in drought (Parsons & Cuthbertson 2001). The burrs are a contaminant in wool, and an annoyance to sheep and wool handlers. The burrs are not generally considered a major vegetable fault in the wool (Parsons & Cuthbertson 2001).
Native ecosystems: Not normally a problem in intact native vegetation. It becomes abundant in areas subjected to long-term drought after rains. It is symptomatic of overgrazing and degraded rangelands (Auld & Johnson 2011).
Urban areas: Not known to be problematic in and around urban areas.
The burrs of Galvanised Burr remain attached to the plant and dispersal occurs when the whole plant dries and breaks off at the base becoming a roly poly, shedding seeds as it is blown by the wind. It is also dispersed when segments of the plant are broken off by animals and catch onto wool or fur. Burrs, each containing one seed, are not readily detached from stems and propagules tend to be pieces of stem with several burrs attached (Auld 1974; Parsons & Cuthbertson 2001).
Galvanised Burr is native to eastern and central Australia, although in New South Wales it is considered a noxious weed in many parts because it invades over-grazed and drought effected paddocks and parts of the plant will collect in wool causing problems for wool handlers. The limits of distribution do not appear to have change between 1934 and 1976 but within these limits considerable fluctuations in population density occurs (Everist 1976).
Galvanised Burr (Sclerolaena birchii)is known to be native in much of the range it is considered problematic. It is also known to have extended its distribution via sheep and cattle in the rangelands where it can also problematic. Eradication of Galvanised Burr is neither practical nor appropriate (Auld & Johnson 2011), and a high level of control is generally not economically justifiable. The over-abundance and prominence of the species is linked to overgrazing and drought (Auld & Johnson 2011) with the aim of a control programs on grazing land to minimise the amount of seed entering the seed bank. This approach will reduce the occurrence and severity of future infestations (DPI NSW 2019).
Chemical control: Spot infestations of Galvanised burr that may appear in the southern grazing areas are readily controlled with non-selective herbicides Government of South Australia, (2014). If herbicide are used, dead plants need to be collected and burnt (Parsons & Cuthbertson 2001) killing the seeds contained with the fruit.
Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au
Non-chemical control: Physical control: can effectively be used Mechanical control: Plants can be grubbed from the ground and heaped for burning using a tractor-mounted blade. Seedlings will establish after the parent plants are removed and cultivation can then be used to control the populations of seedlings. Deep cultivation to bury the seed with pasture improvement and grazing management will give control. Re-infestation can be dealt with by grazing seedlings before they are 6 weeks old (Parsons & Cuthbertson 2001). However grazing management on its own will do little to prevent the plant from re-establishing from seed because the plant germinates mainly in winter when competition from native grasses is minimal (Everist et al. 1976).
Competition and management: Not normally a problem in well managed areas not subjected to over grazing. However, small infestations of Galvanised Burr can be dealt with by careful pasture management, encouraging desired pasture species with topdressing and appropriate grazing, with complete removal of all burrs (containing seed) if possible.
Biological control: There are no biological controls except for the effect of native insects and fungi on the root system of the plant. Studies into the use of these native pests as a control measure where undertaken in the 1930s with little success (Everist et al. 1976).
The seeds of Galvanised Burr do not germinate until part of the burr wall has ruptured. This occurs more quickly when the seed is not buried due to trampling by stock (Auld 1974; Parsons & Cuthbertson 2001). After the burr wall is broken germination will occur any time of the year when sufficient water is supplied (Parsons & Cuthbertson 2001). Galvanised Burr germinates in large numbers after good winter rain and if this is followed by spring or early summer rains a dense stand will result (Everist et al. 1976).
Seedlings cannot survive water stress and will die if follow up rain does not occur. Seedlings become perennial when basal buds form on the crown which allows the plant to resprout after grazing. This occurs at about 6 weeks from germination. First seed is set after 12 weeks and continues through out the life of the plant, usually several years. Mature plants do not live long because damage to the taproot by insects and fungi eventually make it susceptible to water stress (Parsons & Cuthbertson 2001).
It is a short lived perennial herb and many of the mature plants die within two years, and few plants survive for more than four years.
NSW, NT, SA, QLD, VIC, WA
Galvanised Burr is native to New South Wales in semi-arid areas west of the Blue Mountains, and is widespread on sandy soils. Surveys made in 1934 and 1969 showed that the limits of distribution did not change significantly in New South Wales despite what seemed to be an invasion of thousands of hectares. This increase in density was the result of the plants response to an increased incident of summer rainfall during the period and an increase in the amount of degraded and drought effected land across New South Wales over that time (Everist et al. 1976). The spread of Galvanised Burr in New South Wales is limited by rainfall to the west and frost on the tablelands to the east (Parsons & Cuthbertson 2001).
It is also native to semi-arid areas of Queensland and southern Northern Territory (AVH 2021).
It occurs in northern South Australia with some disjunct occurrences in the southern temperate zone which may be due to transportation of seed by cattle and which do not persist (Government of South Australia (2014).
It is considered to be introduced to north-eastern Victoria where it occurs in only a few locations (Walsh & Entwisle 1996).
A recent collection was made from central far east WA, from about 5 km North-East of Eastern end of Morgan Range -near the SA/NT boarder (AVH 2021).
Galvanised Burr is endemic to Australia in summer-rainfall/semi-arid New South Wales, Queensland and the Northern Territory extending into far northern South Australia. It is common in Poplar Box (Eucalyptus populnea) and White Cypress-pine (Callitris columellaris) woodlands on light-textures soils (Cooke 2007).
Not declared in any Australian state or territory.
Woolerino Burr, Blue Burr, Hermdale Lucerne, Galvanised Roly Poly