Quick Facts

Quick facts

  • Innocent Weed (Cenchrus longispinus) is an upright or spreading short-lived grass, growing up to 60 cm tall, with spiny hard fruits containing seeds.
  • It is found mostly in the temperate and humid to tropical climates in sub-coastal and semi-arid areas of south-eastern Australia.
  • A weed of pastures, crops and horticulture, lawns and roadsides and waste areas in a variety of soils from sandy to loamy. 
  • It is spread by burrs which become attached to animals, vehicles and clothing, be dispersed by water and in contaminated agricultural produce.
  • Control methods should aim to prevent seed set and further spread.
  • Controlled via hand-pulling, cultivation before seeding with several required and herbicide application.

What Does It Look Like?

What is it?

Innocent Weed (Cenchrus longispinus) is an upright or spreading, leggy, sparse, annual, biannual or short-lived grass usually growing up to 60 cm tall, but sometimes reaching 90 cm in height. The narrow leaf blades are 3–20 cm long and 3–8 mm wide and are mostly hairless, while the leaf sheaths are hairless or sparsely hairy and often have a reddish or purplish tinge. Where the leaf sheath meets the leaf blade there is a fringe of small hairs 0.5–2 mm long. 

The flower head or inflorescence is a spike 3–7 cm long, the axis flattened and flexuose. The seed head is often partially enclosed within the upper-most leaf sheath are borne on stalks 1–5 mm long, contain a cluster of 8–18 flower spikelets, and each flower spikelet contains 1-3 flowers, each usually produces a single seed.

The fruit (seed) heads are burr-like structures (burrs) that are 3–12 mm across, each bearing usually 40–70 sharp spines that are 3.5–7 mm long and relatively slender. The 'burrs' are a reddish or purplish-green colour when young but turn straw-coloured or brown as they mature and usually detach from the stem. The smooth seeds are 2–4 mm long and 2–3 mm wide and are egg-shaped, but flattened on one side, and remain well hidden within the burrs (Navie 2004).

For further information and assistance with identification of Innocent Weed, contact the herbarium in your state or territory.

Flower colour

Red, Purple, Green, White, Brown

Growth form (weed type/habit)


Where it currently grows? Preferred habitat

Innocent Weed is found mostly in sub-tropical, semi-arid, and warmer temperate environments, and is a weed of disturbed sites, waste areas, roadsides, pastures and cultivation and disturbance. It prefers sandy well drained soils (Navie 2004).

Are there similar species?

Innocent Weed is very similar to another species known as Spiny Burrgrass (Cenchrus spinifex) [as Cenchrus incertus], Mossman River Grass (Cenchrus echinatus) and Buffel Grass (Cenchrus ciliaris). Innocent Weed (Cenchrus longispinus) can be distinguished from these by spiny 'burrs' which are produced on its seed head. These 'burrs' have short stalks and have several rows of larger flattened spines, usually with 40–70 spines in total. In contrast the burrs on Spiny Burrgrass (Cenchrus spinifex) [as Cenchrus incertus] while also having several rows of larger flattened spines, usually with only 8–25 spines in total. The burrs on Mossman River grass (Cenchrus echinatus) do not have stalks and only have one row of larger flattened spines. Buffel Grass (Cenchrus ciliaris) has seed heads that do not produce spiny 'burrs'. Instead, its seed heads bear flower spikelet clusters that have numerous long stiff bristles (Navie 2004).

Why Is It A Weed?

What are its impacts?

Innocent Weed is a weed because of its sharp and clingy burr, its ability to spread rapidly, and tendency to develop into dense infestations in favourable conditions. It is also difficult and expensive to manage, especially in marginal rainfall areas.

Agriculture: Innocent Weed burrs cause a range of problems such as, injury to people and dogs, can become badly tangled in wool thereby lowering its value. There is an economic cost as the burrs slow down shearing resulting in overtime penalty rates as working with contaminated wool requires leather gloves and/or aprons adding to the cost of production. Spines can cause injury to stock resulting in swellings and ulcers in the mouth ulcers in the mouths, and they easily puncture the skin of animals thus affecting the value of hides and they can cause . Fruiting plants are an inconvenience to agricultural workers of irrigated crops. Burrs can contaminate dried fruit crops and lucerne hay (Parsons & Cuthbertson 2001). Although easily controlled in lucerne, burr contamination can reduce the value of lucerne hay. As it is spring-summer growing, innocent weed is not a competitor with the major broad acre-crops.

Urban areas: It also infests some urban areas as a weed of footpaths, bare streetscapes and recreation grounds, although it is less of an issue in maintained gardens and lawns (Government of South Australia 2021).  

How does it spread?

Innocent Weed reproduces by seeds, which are contained within spiny 'burrs'. These 'burrs' are most commonly spread when they become attached to animals, vehicles and clothing, but may also be dispersed by water and in contaminated agricultural produce (Navie 2004). Most seeds germinate within the first few years, but some seeds can survive in the burrs for up to 5 years.

What is its history in Australia?

Innocent Weed history in Australia is unclear partly because of uncertainty over identification, as it is easily confused with another Cenchrus species, called Spiny Burrgrass (Cenchrus spinifex) [as Cenchrus incertus]. Plants were recorded in South Australia in 1886 and were recorded in Victoria in 1895. It was first reported in NSW in 1922 and Queensland in 1930 (Parsons & Cuthbertson 2001).  However, the first herbarium specimens from 

Victoria are from 1901 and 1911; South Australia from1917 and 1921; Western Australia from 1924; New south Wales from 1929; Queensland 1941;  Northern territory in 1957; ACT in 1962 (AVH 2021).

How To Manage It?

Best practice management

Innocent Weed can be controlled by physical and chemical means. Good hygiene practices such as cleaning of machinery and vehicles also aids in controlling spread (Mullen et al. 2005). Once established in dryland areas, innocent weed is very difficult to control because seed may remain viable in the burrs for at least five years. Some seed readily germinates after summer rains, but others in the same burr will remain dormant to germinate later, even skipping a year if there is a shortage of rain in late spring and summer (Government of South Australia 2021). 

Non-chemical control: Preventing seeding is the key to successful control. This can be achieved by cultivation before seed formation, preferably at the seedling stage as larger plants are difficult to turn completely over. Repeated cultivation is necessary to kill subsequent seedlings. Heavy grazing by sheep also prevents seedlings but is not always practical. Well managed pastures also exclude establishment of Innocent Weed.

Chemical control: Application of herbicides to actively growing plants is effective (Parsons & Cuthbertson 2001). Innocent weed can generally be controlled in most irrigated and horticultural crops to prevent contamination of produce, but due to several germination events in one season, repeat treatments may be needed during the growing season. Control of broad acre infestations by herbicide can be prohibitively expensive compared to the income produced from the land.

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

Innocent Weed germination occurs in spring and early summer mostly, but can occur at any time of the year except mid-winter. Vegetative growth is rapid during the growing season if ample moisture is available. Burrs are produced from December to April. Most plants die in autumn or early winter, however some may survive over a mild winter and produce a further small crop of burrs in spring. In some areas it becomes a perennial (living longer than 2 years), regrowing from a crown each spring (Parsons & Cuthbertson 2001). Flowering occurs mostly during summer and autumn (Navie 2004).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

Innocent Weed is a widespread species found mostly in the sub-coastal areas of south-eastern Australia. It is most common in south-eastern South Australia, north-western Victoria and south-western New South Wales. Scattered populations occur throughout the remainder of New South Wales and Victoria, and in south-eastern Queensland. It has also been recorded in Western Australia, the Australian Capital Territory and the Northern Territory (AVH 2021; Navie 2004).

Where does it originate?

Innocent Weed is native to North America and Central America (Navie 2004).

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

Cenchrus longispinus

Other scientific names (synonyms)?

  • Cenchrus echinatus f. longispinus Hack.
  • Cenchrus pauciflorus var. longispinus (Hack.) Jansen & Wacht.
  • Cenchrus echinatus L. (misapplied by Gardner, C.A. 1952, Gramineae. Flora of Western Australia. 1(1): 286.)
  • Cenchrus pauciflorus Benth. (misapplied by Willis, J.H. 1970, A Handbook to Plants in Victoria Edn 2. 1: 204.)
  • Cenchrus tribuloides L. (misapplied by Gardner, C.A. 1952, Gramineae. Flora of Western Australia. 1(1): 288., p.p.)

Does it have other known common name(s)?

Spiny Burr Grass, Burrgrass, American Burr Grass, Innocent Weed, Innocent-Weed, Gentle Annie, Mat Sandbur, Coast Sandbur, Sand Burr, Sandbur, Sandspur, Longspine Sandbur, Field Sandbur, Field Bur, Hedgehog Grass, Bear Grass, Bohena Beauty

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