Quick Facts

Quick facts

• Wheel Cactus (Opuntia robusta) is an invasive species which is currently naturalised in New South Wales, Victoria and is expanding its distribution in parts of South Australia and known mainly from the shire of Merredin in Western Australia.
• Fragments of stem segments, flowers and immature fruits will root and produce new plants.
• The succulent fruits are eaten by birds and animals and they distribute the seed in their droppings.
• It reduces land productivity and can cause injury to humans and other animals.

What Does It Look Like?

What is it?

Wheel Cactus (Opuntia robusta) is an upright shrub, commonly 1–2 m but occasionally to 3.5 m tall, and 1–3 m across. The main stems are much branched and the flattened stem segments (pads) are almost circular, distinctly bluish green to bluish grey with a powdery bloom, commonly 20–30 cm, but up to 47 cm diameter and to 2.5 cm thick. The areoles (circular raised spots) have numerous small bristles (glochids) and 1–12 white to yellow spines to 4 cm long.

Flowers are yellow, 5–8 cm diameter, commonly along the margins of the pads.

Fruits are green turning red to reddish purple when ripe, succulent, barrel-shaped or rounded, 6–8 cm long, up to 6 cm diameter. Seeds are pale brown and numerous (Anderson 2001; Navie 2004; Chinnock pers. comm 2007).

For further information and assistance with identification of Wheel Cactus contact the herbarium in your state or territory.

Flower colour

Yellow

Growth form (weed type/habit)

Shrub

Where it currently grows? Preferred habitat

Wheel Cactus is widespread in arid and semi-arid areas where it grows on a wide variety of soils on flats or on hills or ranges (Parsons & Cuthbertson 2001; Chinnock pers. comm. 2007).

Are there similar species?

Wheel Cactus is quite distinctive because of the large rounded bluish or green/bluish grey pads, however the following species may be confused with it:

• Opuntia engelmanii is a low growing shrub 0.4–1.2 m tall. Lateral branches creep along the ground. The pads are rounded and deep green. The yellow flowers are similar to Wheel Cactus although the stigmas are deep green.
• Common Prickly Pear (Opuntia stricta) is a low-growing shrub up to 1 m tall. The pads are pale green with a whitish bloom, obovate to elliptic, 10–35 cm long, lacking spines (spiny forms of this species do not overlap with Wheel Cactus). It has relatively large yellow flowers 6–8 cm across and reddish-purple fruit.
• Indian Fig (Opuntia ficus-indica) is a shrub or small tree commonly 1.5–3 (5) m tall. It has large flattened, elongated obovate to elliptic pads 25–50 cm long that are usually spineless. It has relatively large yellow flowers 7–9 cm in diameter. The fruit are reddish purple. It rarely has any spines on its stem segments and if present they are weak and usually deciduous.
• Velvet Tree Pear is a tall shrub or small tree to 6 m tall with flattened and elongated, finely hairy, oblong or elliptic, pads. It has relatively large orange-red coloured flowers 4–5 cm diameter and red pubescent fruit (Telford 1984; Navie 2004; Chinnock pers. comm. 2007).

Why Is It A Weed?

What are its impacts?

Agriculture: Wheel Cactus can form dense populations and impede movement and lay waste to pastoral and agricultural land. Spines can cause damage to lips and tongues of stock if eaten and dense thickets impede stock movement, while providing harbor for pest animals.

Native ecosystems: Occurs in Eucalyptus and Mallee systems.

Human impacts: The sharp spines and prickles can prove difficult to remove if they penetrate human skin (Parsons & Cuthbertson 2001; Chinnock pers. comm. 2007).

How does it spread?

Wheel Cactus readily reproduces from stem fragments, flowers and immature fruits and seeds. Roots will develop from areoles on the side in contact with the substrate and one or a number of shoots will emerge from the upper side or margin. Plants can be distributed by fragments moving down slope in hilly country or washed down creeks during periods of flow. Wheel Cactus fruits are frequently eaten by birds including emus and probably native marsupials and foxes. It is frequently encountered in dense populations under and around large eucalypts where birds roost. Plants grow rapidly and can reproduce in 3–4 years from seed (Parsons & Cuthbertson 2001; Chinnock pers. comm. 2007).

What is its history in Australia?

The date and method of introduction is unknown, but it was probably introduced as an ornamental and was proclaimed as a weed in Victoria in 1961 (Hosking et al. 1988).

How To Manage It?

Best practice management

Non-chemical control: Can be controlled by removing plants or burning.

Chemical control: Externally applied chemical spray and internal injection of herbicide can be very effective.

Biological control: Wheel Cactus can also be controlled by the cochineal insect (Dactylopius opuntiae) although it appears that this cochineal is more effective on some populations than others. The insect can be spread easily by transferring portions of infected pads to isolated unaffected plant (Edmunds 2006).

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

Does it have a biological control agent?

YES

When does it grow? (lifecycle/growth calendar)

Wheel Cactus is most active during the warmer months especially between November and March. Flowering occurs between October and December and fruits start ripening between February and April. Seed will germinate at anytime during the year depending on rainfall and seedlings will flower in three to four years (Parsons & Cuthbertson 2001; Chinnock pers. comm. 2007).

Where Is It Found?

Which states and territories is it found?

NSW, SA, VIC, WA

What areas within states and territories is it found?

Wheel Cactus is widespread in the Flinders Ranges, Eastern and Murray regions of South Australia, north central Victoria and western New South Wales (Chinnock pers. comm. 2007). Occurs in the areas around the Merredin Shire in Western Australia.

Where does it originate?

Wheel Cactus is a native of northern and central Mexico. In its native habitat it is rare and endangered and is listed on the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II (GRIN 2007).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

YES

Where is it a declared weed?

Declared in all states and territories.

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Opuntia robusta

Does it have other known common name(s)?

Wheel-pear, Wheel Pear