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Alkali sida (Malvella leprosa)

Alkali sida is an introduced perennial weed that competes strongly with pasture plants, particularly on alkaline soils and in irrigated pastures. Its Australian infestations are currently small, but it can form dense colonies and may be toxic to sheep if eaten in large quantities.

Key facts

Type: Weed, herb.

Native to: Western and southern North America.

Established in: VIC, SA.

Other names: Ivy-leaf Sida, Alkali Mallow.

Best time to act: Look for rapid growth in spring and treat during active growth before flowering, which mainly occurs from December to February.

Identification

  • A low-growing, semi-erect perennial herb reaching about 35 cm tall, with slender stems up to 50 cm long.
  • Its greyish-green leaves are densely covered in star-shaped hairs and are kidney-shaped to fan-shaped, about 1–3.5 cm long and 1.5–4.5 cm wide.
  • White to yellow, five-petalled flowers are about 2.5–3.5 cm across and grow in leaf axils or small clusters at branch ends.
  • The cone- or disc-shaped fruits contain 6–10 dark brown, roughly textured seeds.
  • It regrows from perennial roots, which can be deep and extensive.
  • Look-alike: Spinyhead sida, Flannel weed and Paddy's lucerne have similar flowers, but differ in overall growth form and leaf shape; alkali sida has kidney- to fan-shaped leaves and a small epicalyx of linear lobes at the base of the calyx.
  • Look-alike: Spinyhead sida and Flannel weed are taller shrubs with spear-shaped or larger oblong leaves, while Paddy's lucerne is a taller, branched shrub with oblong to spear-shaped leaves.

Where it grows

In Australia it occurs in New South Wales, Victoria and South Australia, chiefly in annual crops, irrigated pastures and channel banks on alkaline soils.

Why it matters

  • It competes strongly with pastoral species, especially on alkaline soils, and can form dense colonies that restrict growth and replace pasture biomass.
  • The current Australian infestation area is small and is thought to have only a minor impact on crop yield.
  • It is usually avoided by grazing livestock but can be toxic to sheep in large quantities, causing hairball blockages in the intestines.
  • It may have a minor effect on grassland flora and reduce food sources for some native fauna.

How it spreads

  • Root fragments and seeds can be moved in contaminated soil, produce and machinery; root fragments can resprout and produce new plants.
  • Seeds or capsules can spread in water, on livestock coats and in clothing.
  • Cultivation and transport of contaminated soil can move the weed to clean areas, and it can establish in irrigation channels and encroach into adjoining pastures.

Control options

  • Repeated applications of registered herbicides during active growth before flowering are the only currently effective control described for depleting the extensive underground roots.
  • Above-ground growth dies back in autumn, but cultivation does not control the roots and may spread the plant.
  • Livestock grazing is not a reliable control and may encourage spread by removing competing plants; alkali sida is considered moderately palatable to goats, which may be useful for control in pastoral areas.
  • Avoid applying herbicides close to vines or horticultural crops where vapour drift could cause damage.

Hygiene and washdown

  • Keep contaminated soil, produce and machinery from being moved to clean areas because root fragments and seeds can spread this way.
  • Check livestock coats and clothing for capsules that could carry seeds.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: State prohibited weed. State prohibited weeds are the highest priority: the Victorian Government is responsible for eradicating them, so report any sighting to Agriculture Victoria.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board

Sources