APC (2020). Australian Plant Census, Council of Heads of Australasian Herbaria (CHAH). Available at: https://biodiversity.org.au/nsl/services/apc. [accessed 16/11/2020]
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White Weeping Broom (Retama raetam) is a Mediterranean, densely branching shrub that grows to about 3 metres tall and may reach 6 metres across. Plants are grey-green with many slender, drooping pendent branches. Stems of young plants are covered with long soft hairs but become hairless with age. Young plants are wispy with a single stem and strong taproot. The leaves, which are very small (about 5 mm long) and narrow (only 1 mm wide), are quickly dropped and the plant remains leafless for most of the year, most of the time leaves are not seen, and the grey-green branches contain chlorophyll that allow photosynthesis. The lack of leaves, that reduce water loss make it ideally suited to the warm dry conditions (DPI NSW 2019).
Flowers are typically pea-like, 8–10 mm long, white, in racemes (along the branches) of 3-15 flowers. The calyx (at the base of the flower) is dark red-brown in colour. Each flower has 10 stamens forming a closed tube.
The fruit (seed pod) is wide obovoid (egg-shaped in outline with the widest part nearer the tip), 10-15 mm diameter, glabrous (hairless), with a short mucro (point tip) or an erect or curved beak. The pod is fleshy at first, later leathery, smooth or wrinkled. Each pod has one or two kidney-shaped seeds, which are about 6.5 mm long x 5 mm wide, and may be yellow, green, brown or black in colour (CRC 2003).
For further information and assistance with identification of White Weeping Broom contact the herbarium in your state or territory.
Like many of the Broom plants, White Weeping Broom (Retama raetam) invades nutrient-poor to fertile, well-drained (especially sandy) soils where it can fix nitrogen and form a scrub layer that can out compete and shade out native plants. This species is possibly the most drought tolerant of the exotic Brooms in Australia, making it a particular threat in dry regions and during drought years. White weeping broom has several adaptations, including its lack of leaves, that reduce water loss and make it ideally suited to the warm dry conditions of its native range (DPI NSW, 2019).
It may infest grazing land and prevent access to stock. It is also probably the least palatable to stock of the exotic brooms (CRC 2003), it is toxic and cause death in domestic animals. While it has high tolerance to drought and frost and moderate fire and salt tolerance it is not tolerant of waterlogging (DPI 2007).
White Weeping Broom (Retama raetam) is extremely similar looking and closely related to the species, Retama monosperma, a popular garden plant in Australia and also a potential weed (CRC 2003). White Weeping Broom may also be confused with White Spanish Broom (Cytisus multiflorus) and Scotch Broom (Cytisus scoparius). However, the pods in Retama species are inflated, do not release their seeds explosively and plants are leafless for most of the year unlike both White Spanish Broom and Scotch Broom (Jafri & El-Gadi 1980; Cullen et al. 1995).
White Weeping Broom (Retama raetam) is on the Alert List for Environmental Weeds, a list of 28 non-native plants that threaten biodiversity and cause other environmental damage. Although only in the early stages of establishment, these weeds have the potential to seriously degrade Australia's ecosystems (CRC 2003). White Weeping Broom is possibly the most drought tolerant of the exotic brooms in Australia, making it a particular threat in dry regions and during drought years DPI NSW (2019).
Agriculture: White Weeping Broom has the potential to become a significant threat to Australia's pastoral industry if it escapes containment (CRC 2003). It may infest grazing land and reduce access by stock. In addition, it is generally unpalatable, but toxic, and the toxins in the plant can taint milk and may poison nursing animals. It could reduce carrying capacity of grazing lands by more than 5% (DPI 2007). It is also probably the least palatable to stock of the exotic brooms DPI NSW (2019), but if eaten, all domestic species are susceptible to intoxication which can kill (Bahri et al, 1999).
Native ecosystems: White Weeping Broom is a potentially serious invader of natural vegetation (CRC 2003).
Urban areas: White Weeping Broom also has the potential to invade vegetation around communities especially small coastal communities and to spread throughout such areas via roadsides
White Weeping Broom (Retama raetam) reproduces only from seed. Long distance dispersal is via seeds that have, or will, spread from gardens to surrounding suitable environments. Each plant produces hundreds of seed pods and up to thousands of seeds on larger plants. The seeds drop when the seed pods split open, and can be further spread by water. A hard seed coat renders most seeds dormant initially, but as the seed coat wears away germination can take place. Seeds remain viable in the soil for several years (CRC 2003), potentially more. It is not known to sucker.
White Weeping Broom (Retama raetam) was brought to Australia as an ornamental shrub. It was first recorded in South Australia in 1841 (CRC 2003).
White Weeping Broom (Retama raetam) is is not widespread in Australia and the preferred method of control has not yet been fully developed. However, experience in controlling other WoNS brooms including Cytisus scoparius, which is a major weed in southern Australia, could be applied to White Weeping Broom (Office of Environment and Heritage. 2014). Any control of White Weeping Broom should be undertaken cooperatively with your state or territory weed management agency or local council (CRC 2003). Once an area of White Weeping Broom has been treated, it will be necessary to monitor the treated area for many years and destroy new plants (CRC 2003; DPI NSW 2019).
Chemical control: No herbicides are registered for control of White Weeping Broom. In the case of Cytisus scoparius, chemical control is effective in the short term but is expensive and needs to be followed up for many years until the seedbank has been depleted. There is also a risk of damage to non-target species. Some useful herbicide control methods for the WoNS brooms can be seen in Office of Environment and Heritage (2014) and DPI NSW (2019). Please follow your States or Territories guidelines, contacting relevant authorities if you are unclear, and follow herbicide label information before proceeding. Herbicide application methods for other weedy brooms include:
Foliar spraying: For the application of herbicide solution to weed foliage in the form of a spray, a common method used for woody plants. Foliar spraying can be used to treat plants of all ages but can be less effective on older plants.
Cut-and-swab method (Cut stump treatment): is when each stem is cut off at ground level and immediately applying herbicide to the cut surface killing the plant to prevent regeneration from the rootstock.
Basal barking: This method involves applying herbicide mixed with an adjuant to the lower trunk or stem of woody plants up to around 50 mm in diameter to a height of 30-40 cm above ground level.
Stem injection (drill-and-fill): Stem injection delivers herbicide directly to the sapwood but is rarely used on brooms, but when used, it is for plants with stems over 50 mm in circumference.
Scrape-and-paint: This method involves scraping away a small section of the bark and applying herbicide directly onto the sapwood. It is an effective but rarely used technique normally used on larger plants.
Splatter or gas gun: splatter guns were developed over thirty five years ago for sheep drenching and has been adapted for weed spraying using chemicals.
Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .
Non-chemical control: Physical control: Physical removal is an option for isolated plants, especially if they have not seeded; although seedlings are hard to hand pull, tools can be used making removal easier. However, it will be necessary to monitor the treated area for many years and destroy any new plants that germinate from the soil seed bank.
Mechanical control: Bulldozing infestations into heaps and burning the resulting weed mounds has been a common method used to control Broom but it only provides a temporary solution. Bulldozing causes massive soil disturbance, and physical movement of plants not only burying seeds but also spreading them beyond the original infestation.
Fire: Fire effectively kills plants and can help to break seed dormancy. Experience using fire to control other species of broom indicates that it kills a large proportion of seeds but lightly scorched plants may re-sprout. Follow-up chemical treatment after fire will probably be needed for many years until the seed-bank is depleted. Usually though, fire is not recommended to control broom in Australia due to the risk of out-of-control fires and because it leaves the land initially unusable, with many burnt stems remaining in the ground (CRC 2003).
White Weeping Broom (Retama raetam) flowers from late winter to mid spring and sheds its seed pods in late spring to early summer. Growth occurs whenever there is moisture, but mainly from autumn to spring. Seeds mainly germinate in autumn, but can germinate year round under suitable conditions (CRC 2003). Cultivated plants have been recorded as producing fruit within 5 years of planting (Johnson 2005).
SA, NSW, QLD, TAS, WA
In Australia White Weeping Broom (Retama raetam) has become naturalised in South Australia, particularly around and to the east of Adelaide, on the Yorke Peninsula where it has taken over an area planted to native vegetation, and on the Eyre Peninsula where it is invading She-oak (Casuarina, Allocasuarina) woodlands. In Western Australia it grows around and to the north of Perth (CRC 2003). Occurrences in NSW, QLD and TAS are currently limited.
White Weeping Broom (Retama raetam) is native to northern Africa and western Sahara, Sicily and the Middle East. In its native range, White Weeping Broom grows in grasslands in the Mediterranean region and is a common feature of deserts and grasslands in the Sahara (CRC 2003).
White Broom, Ratamals