Quick Facts

Quick facts

  • Paddy's Lucerne (Sida rhombifolia) is a serious competitor for light and nutrients in both crops and pasture.
  • It is a common component of pastures on the east coast of Australia, smothering all grasses in some cases.
  • Paddy's Lucerne is not readily grazed and is of low nutrient value.
  • Although not poisonous to stock, when it is eaten, there is always a danger of 'hair-balls' forming from the stringy bark of the plant.

What Does It Look Like?

What is it?

Paddy's Lucerne (Sida rhombifolia) is an upright, perennial sub-shrub which may be up to 1.5 m tall and when young has quite a dense covering of minute hairs. These are mostly lost as the plants mature. The leaves are egg-shaped, oval-shaped or rhombic in outline and 15–90 mm long. The upper two-thirds of the leaf blades are shallowly toothed.

The yellow flowers are about 15 mm across and are borne singly along the stems (that is, there is one per leaf axil) and become more crowded towards the tip of the stems. The flower-stalks are up to 35 mm long when the flower first opens but grow longer as the fruit matures.

The outer whorl of the flowers (the calyx) encloses the mature fruit. The fruit (called a schizocarp) is 4.5–5.5 mm in diameter. It splits into 9–11 segments called mericarps. Each mericarp is about 2.5 mm high and usually splits in half at the apex, with each apex being awned. The awns are about 0.8 mm long, hairless or sparsely hairy. Very occasionally single-awned mericarps are present instead of the usual 2-awned mericarps (Barker, unpublished manuscript).

For further information and assistance with identification of Paddy's Lucerne contact the herbarium in your state or territory.

Flower colour


Growth form (weed type/habit)


Where it currently grows? Preferred habitat

Paddy's Lucerne is a weed of cultivated and otherwise disturbed sites such as roadside verges and degraded pastures in tropical to warm-temperate climates. It tolerates a range of soil types (Parsons & Cuthbertson 2001; Navie 2004).

Are there similar species?

Paddy's Lucerne is most likely to be confused with other species of Sida, especially Flannel Weed (S. cordifolia) and Spinyhead Sida (S. acuta). It may also be confused with S. spinosa, S. subspicata, Malvastrum americanum and M. coromandelianum (Navie 2004).

Paddy's Lucerne has oval (elliptic), lance-shaped (lanceolate) or diamond-shaped (rhomboid) leaves with a dense covering of hairs on their undersides and a sparse covering of hairs on their upper surfaces. These leaves usually have rounded tips (obtuse apices). Its flowers are borne singly on long and thin stalks (10–40 mm long) and their bracts (calyces) are sparsely hairy. The fruit usually break up into 8–12 mericarps that are topped with two short awns (0.5–1 mm long) (Navie 2004).

Flannel Weed has broad or heart-shaped (cordate) leaves that are densely covered in small whitish coloured hairs (on both surfaces) that give them a felty texture. Its flowers are borne in small, dense, clusters on short stalks (2–4 mm long) and their bracts (calyces) are densely hairy (unlike the sparsely hairy bracts of Paddy's Lucernne). The mericarps have longer, slender awns (2.5–3.5 mm long) (Navie 2004).

Spinyhead Sida has elongated (lanceolate) leaves that are hairless or sparsely hairy on both surfaces and have pointed tips (acute apices), not rounded as in Paddy's Lucerne. Its flowers are borne singly or in small clusters on short stalks (2–8 mm long). The fruit break up into 5–8 wedge-shaped mericarps (Navie 2004).

Spiny Sida has flowers are borne singly or in small clusters on relatively short stalks (3–15 mm long). The fruit usually break up into only 5 mericarps (Navie 2004).

Spiked Sida (Sida subspicata) has relatively narrow (lanceolate) to broad (ovate or oblong) leaves with a dense covering of hairs on both surfaces (but more so underneath). Its flowers are almost stalkless and borne in elongated clusters (spikes) with a few small leaves sometimes interspersed between them. Their bracts (calyces) are finely hairy and the fruit break up into 4–6 mericarps that have rounded tips (Navie 2004).

Malvastrum species can be distinguished from Sida species because the flowers have what is known as an epicalyx, in this case 3 free segments situated immediately below the calyx, which species of Sida lack (Barker, unpubl. manuscript)

Why Is It A Weed?

What are its impacts?

Agriculture: Paddy's Lucerne is a serious competitor for light and nutrients in both crops and pastures. It is becoming a problem in soybeans and vegetable crops in Brazil, cotton in the United States and peanuts, tobacco and pastures in Australia. It is a common component of pastures on the east coast of Australia, smothering all grasses in some cases. Its seed may contaminate harvested material. It is not readily grazed by livestock and is of low nutrient value, although it has, at times, been considered valuable cattle feed on the North Coast of New South Wales. It is not poisonous to stock but, when animals eat it, there is always a danger of 'hair-balls' forming from the stringy bark (Pitt 1998; Parsons & Cuthbertson 2001).

Native ecosystems: While Paddy's Lucerne is mostly an agricultural weed it is also a weed in grasslands and woodlands (Navie 2004). It is an invasive shrub that can compete with and exclude native species on degraded or overused land (Smith 2002).

How does it spread?

Paddy's Lucerne reproduces and disperses only by seed which can catch in fibrous material, e.g., clothing and animal fur/hair. Seed is also spread in streams and irrigation water, as impurities in hay and pasture seed, and in mud sticking to footwear, hooves, machinery and vehicles (Parsons & Cuthbertson 2001).

What is its history in Australia?

Paddy's Lucerne was possibly brought to Australia for fibre production as it produces a very good quality hemp (Barker, unpubl. manuscript).

How To Manage It?

Best practice management

Non-chemical control: Control methods for Paddy's Lucerne are the same as for Spinyhead Sida and Flannel Weed. Small outbreaks can be grubbed out before flowering, with care being taken to cut the root well below the surface to prevent or minimise regrowth. Larger areas can be controlled through repeated cultivation but this may not be practical.

Generals slashing of plants before flowering help reduce seed production in infected areas. The spread of seed from infected paddocks to uninfected paddocks can be reduced if stock are yarded for four to five days before hand, this allowing time for digested seed to have been excreted and seed attached to their hides to have been brushed off (Parsons & Cuthbertson 2001).

Sowing of well-fertilised "improved" pastures results in a more dense pasture which inhibits the growth of Paddy's Lucerne. However, care should be taken when deciding what to plant. Pasture species such as Buffel Grass are also serious environmental weeds (Parsons & Cuthbertson 2001).

Chemical control: Seedlings to 10 cm high are susceptible to early post-emergence herbicides, but plants become resistant to most herbicides as they mature (Parsons & Cuthbertson 2001).

For general information of the use of chemicals please visit the Australian Pesticides and Veterinary Medicines Authority at http://www.apvma.gov.au 

Biological control: Paddy's Lucerne has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. The chrysomelid beetle Calligrapha pantherina has been a successful biological control agent of Spinyhead Sida (S. acuta) and has also been released on Paddy's Lucerne at a number of sites in Queensland. It established at several sites in north Queensland, but failed to establish on populations in southern Queensland. C. pantherina was released in NSW in 1990 and that the beetles Calligrapha felina and Acanthoscelides brevipes were being investigated as possible control agents in the Northern Territory (Julien & Griffiths 1998; Parsons & Cuthbertson 2001).

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

There seems to be little recorded information on the life cycle of Paddy's Lucerne. In northern Australia seed begins germinating after the opening rains at the end of the dry season, i.e. in September/October, and continue to emerge during the wet season. Flowering in this region is probably mostly from about December to April. In areas retaining moisture plants may grow throughout the year but plants commonly become dormant during the dry season, with new growth appearing at the rootstocks at the next onset of the rainy season (Parsons & Cuthbertson 2001).

Much of Paddy's Lucerne seed is dormant when shed. In the field, soil acids and microbial activity together with expansion and contraction of the seedcoat, under the influence of alternating temperatures on the soil surface, eventually crack the outer covering and admit water. Germination commences at 20 °C and has an optimum range between 25 °C and 32 °C. Under favourable conditions, seedlings can emerge from depths of 4 cm and plants grow well in day:night temperature regimes of 30 °C:25 °C (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

Paddy's Lucerne is widespread throughout Australia, occurring in all mainland States. It is particularly common in the coastal and near coastal areas of eastern Australia (from Cairns to southern New South Wales), and is also common in much of the Northern Territory and northern parts of Western Australia. It is also present in parts of south-western Western Australia, South Australia, Victoria, central-western Queensland and central-western New South Wales (Navie 2004; AVH 2007).

Where does it originate?

Paddy's Lucerne is native to tropical America but now a pantropical weed (Barker, unpublished manuscript)

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Sida rhombifolia

Other scientific names (synonyms)?


Does it have other known common name(s)?

Common Sida

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