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Slender buttonweed (Spermacoce exilis)

Slender buttonweed is an introduced plant naturalised in Australia, where it grows in disturbed, humid sites at low elevations. It can be easy to miss among low vegetation, and it may flower and fruit for much of the year.

Key facts

Type: Weed, herb.

Native to: Neotropics; its exact native origin is unknown..

Established in: QLD.

Other names: Borreria exilis, Spermacoce mauritiana, Spermacoce repens, Spermacoce decandollei.

Best time to act: Inspect throughout the year, as plants may flower and fruit almost year-round, and treat before capsules release seed.

Identification

  • A slender, creeping to weakly ascending herb that can grow to 30 cm tall; it may be annual or perhaps perennial.
  • Stems are four-angled, with narrow, often hairy wings; the leaves are small, opposite-looking, and ovate to elliptic-oblong, with very short or no stalks.
  • Small clusters of flowers, 3 to 6 mm across, occur at stem tips and in the upper leaf axils; the flowers are white and have two calyx lobes.
  • The small, ellipsoid capsules are about 1 to 1.1 mm long and contain shiny, brownish-yellow seeds.
  • Look-alike: It can be confused with Spermacoce prostrata and other small buttonweeds; identification may require close examination of the flowers and fruit.

Where it grows

In Australia it is recorded from disturbed, humid sites at low elevations.

Why it matters

  • It is a naturalised weed of disturbed ground and can compete with desirable low-growing vegetation where it establishes.
  • Its small size and creeping growth can make plants easy to overlook during site inspections.
  • Flowering and fruiting almost year-round can make it harder to time detection and control to a short seasonal window.

How it spreads

  • The plant produces small seeds in capsules, so avoid moving fruiting plants or contaminated soil.
  • Seeds may be spread when soil or plant material is moved on vehicles, machinery, boots or equipment.

Control options

  • For small patches, hand-pull or dig out plants, removing the roots and collecting any capsules or seed-bearing material.
  • Dispose of removed plants and seed-bearing material in accordance with local waste and biosecurity advice; do not spread it in green waste or soil.
  • For larger infestations, use only herbicides registered for the site and target plant, or other approved methods, and follow the product label and local requirements.
  • Revisit treated sites and check nearby disturbed ground for regrowth or new seedlings; contact the relevant state or territory biosecurity agency for advice where appropriate.

Hygiene and washdown

  • Before leaving an infested area, remove soil and plant material from boots, vehicles and machinery, and contain the clean-down waste.
  • Avoid transporting soil or plant material that may contain seeds to clean sites.
  • 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: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • 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.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)

Sources