Opuntoid Cacti

Opuntia species, Cylindropuntia species Austrocylindropuntia species

Synonyms -

Family: Cactaceae

Names:

Opuntia is Latin of unknown relevance but may refer to the town of Opus.

Other Names:

Summary:

Opuntoid cacti belong to 3 closely related genera, Opuntia, Cylindropuntia and Austrocylindropuntia. They are shrubs or small trees up to 6 m high which have green stems which are succulent and modified into jointed cylindrical or compressed and usually spiny segments. The leaves when present are reduced to small scales at the base of the spines. The flowers are single and stalkless, variable in colour from purple, pink, orange to yellow, large, 2-10 cm in diameter with numerous widely spreading numerous petals. The fruits are fleshy berries, brightly coloured (green, orange, red or purple), longer than wide and flattened or depressed from above. Some prickly pears may reproduce vegetatively by fragmentation of the stems.
Prickly Pears were often cultivated as garden ornamentals but have persisted and spread from old settlements particularly in the Goldfields, Gascoyne and Pilbara regions. Most species are native to South America, Mexico or southern USA.

Species of Opuntoid Cacti that appear to have naturalised in WA are:
Austrocylindropuntia cylindrica is at Kulin
Cylindropuntia fulgida (Coral Cactus)is an erect plant with crowded cylindrical stem segments.
Cylindropuntia imbricata (Devil's Rope) is a single infestation between Kalgoorlie & Wiluna
Cylindropuntia rosea (was Cylindropuntia tunicata) (White-spined Hudson Pear) is a low shrub to 60 cm high with dull grey green elongated cylindric segments. The flowers are yellow. The yellow fruit is barrel shaped and slightly lumpy.
Opuntia elata is single infestation between Kalgoorlie & Wiluna
Opuntia elatior is a single infestation at Haig on the Nullarbor.
Opuntia engelmannii is a shrub to 2 m high with flattened dull green to grey green oval to circular segments. The flowers are yellow. The fruits are red to purple, barrel shaped or egg shaped and often lumpy. There is one infestation at Wialki 260 km NE of Perth in WA.
Opuntia monacantha (Smooth Tree Pear) has been found in Perth and Gwalia near Leonora North of Kalgoorlie.
Opuntia monacantha (was Opuntia vulgaris) (Barbary Fig) is a tree-like shrub to 3.5 m high with flattened shiny green oblong segments, the upper segments often drooping. The flowers are yellow, sometimes tinged red. The red to purple berries are egg shaped. It has been found in Perth and Gwalia near Leonora North of Kalgoorlie.
Opuntia stricta (Common Prickly Pear) is a shrub 1-3 m high with flattened dull green to blue green oval stem segments. The flowers are yellow. The berries are red to purple. This species is very poorly mapped in WA.

Description:

Cotyledons:

Two.

First leaves:

Leaves:

The leaves when present are reduced to small scales at the base of the spines.
Stipules - None.
Petiole - None.
Blade - Small.

Stems:

Green stems which are succulent and modified into jointed cylindrical or compressed and usually spiny segments. Jointed stem segments called pads or cladodes.
Pads - Have small depressions called areoles on their surface. Areoles are the points where spines, glochids, new pads and flowers grow.
Spines may provide protection from predators, evaporating winds and may channel moisture depending on the arrangement and species.

Flower head:

The flowers are single and stalkless.

Flowers:

Variable in colour from purple, pink, orange to yellow, large, 2-10 cm in diameter with numerous widely spreading numerous petals.
Ovary -
Sepals -
Petals - Many.
Stamens -
Anthers -

Fruit:

The fruits are fleshy berries, brightly coloured (green, orange, red or purple), longer than wide and flattened or depressed from above.
The fruit may also have areoles.

Seeds:

Seeds may have a hard seed coat which provides longevity.

Roots:

Usually shallow rooted. Roots may form from areoles on stem segments.

Key Characters:

Distinguished from other sub families by the presence of glochids which are small detachable barbed bristles that grow from the areoles.
Austrocylindropuntia have no papery sheaths around their spines and cylindrical to club shaped segments.
Cylindropuntia have cylindrical segments and a papery sheath around the spine that separates after the firs year.
Opuntia have flattened segments called pads which are usually roundish.

Biology:

Life cycle:

Usually perennial and long lived.
Seeds can germinate at any time of year when rain occurs. Vegetative spread is the main method of multiplying.

Physiology:

They use CAM (Crassulacean Acid Metabolism) photosynthesis so that gas exchange may take place during the cooler night environment when moisture loss is minimised.
Segments can survive for extended periods without soil or water.
Pieces in sealed bags stored indoors were still viable after 3 years.

Reproduction:

By seed in most species and segments.

Flowering times:

Usually spring and summer with fruits forming by autumn.

Seed Biology and Germination:

Has dormant seed

Vegetative Propagules:

Stem fragments.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Spread by seed or stem segments depending on the species.
Stem segments may attach to animals or machinery for spreading.
Long distance spread is usually by intentional planting or dumping of garden refuse.

Origin and History:

Some introduced to start a cochineal industry.
Austrocylindropuntia are from South America.
Cylindropuntia are from central America and the West Indies.
Opuntia are from the Americas and West Indies.

Distribution:

NSW, NT, QLD, SA, VIC, WA.

Courtesy Australia's Virtual Herbarium.
Brown dots = Opuntia spp.
Red dots = Cylindropuntia spp.
Blue dots = Austrocylindropuntia spp.
The cacti are poorly mapped however some large infestations occur such as 35,000 ha of Wheel Cactus in the Flinders Ranges, 60,000 ha of Hudson Pear near Lightning Ridge and 200,000 ha Tiger Pear in NSW.

Habitats:

Climate:

Prefer areas with more than 150 mm annual rainfall.

Soil:

Tolerate a range of soil types.

Plant Associations:

Significance:

Prickly Pear used to be the most important Australian weed. In 1925, 24 million hectares was infested in Queensland and New South Wales. Half of this had infestations that were so dense that the land had no productive value. In 1920, 400,000 ha a year was being forced out of production. Biological control with the larva of the Cactoblastis moth introduced in 1925 reduced the infestation by 90% by 1933. Today only isolated infestations are found where biological control agents are still working. In some cooler areas where the insects are not so active it still causes problems.

Beneficial:

Ornamental and hedge plant.
Host for the cochineal insect for making cochineal dye.
Some species have edible fruit or the stem segments can be candied to form a chewy sweet or boiled as a vegetable after removing spines & barbs.
Used in herbal remedies for whooping cough and diabetes.
Eaten by stock during droughts.
Honey plant.
Spines used as gramophone needles.

Detrimental:

Sharp spines may cause injury or contaminate wool, hides and produce.
Competes with other vegetation.
Restrict access to water or grazing area.
May harbour vermin such as rabbits.
The fruits are breeding grounds for fruit fly.

Toxicity:

Bacterial infection of the tongue may occur where spines cause damage.
Causes 'wooden tongue' in sheep.
May cause fibre balls in the stomach.
Excessive consumption of fruit may cause kidney disorders in humans.

Legislation:

Declared in all states.
Weed of National Significance (WONS)

Management and Control:

MSMA, triclopyr, picloram + triclopyr and amitrole are used for control.
Stem injection or overall spraying can be used depending on the species. Several treatments are usually required. Best results usually occur when the plants are actively growing and thoroughly covered.
Fire may be used to improve access for other control.

Thresholds:

Eradication strategies:

Physical removal and burning in wood fire heaps together with cultivation and removal of the root system is still used for small accessible infestations. Many infestations are not accessible and herbicides including triclopyr, picloram, hexaflurate, amitrole and MSMA are used to aid control. Use an overall spray and then cut the larger plants down the centre and re spray the cut basal section.
For Opuntia species with large stems, high levels of control may be achieved by drilling a 1 cm hole about 10 cm deep into the base of the major stems and filling it with 10 mL MSMA. Space the holes about 20 cm apart on large plants. A cordless drill with a 75 cm long bit and a converted drench gun with a 75 cm long probe is often used to reduce the risk of operator injury from the spines. Burn if possible. Repeat injections every autumn and spring until no more plants are found. If seedlings become an issue spray the area with picloram + triclopyr plus an organosilicone adjuvant in water.
For smaller stemmed species, spray the infestation until just wet with 1 L Access® in 60 L diesel in spring or autumn and follow up 6 months later. If seedlings become a problem use 1 L picloram + triclopyr (e.g. Grazon®) plus 1 L spray oil in 100 L water and spray the remaining plants and surrounding ground until just wet.
Small quantities of collected material may be killed by deep freezing at -200C for 48 hours.

Herbicide resistance:

None reported.

Biological Control:

Cactoblastis moth introduced to control Prickly Pear in 1926.

Related plants:

There are no Australian native plants in the Cactaceae sub family.
There are about 30 species naturalised in Australia.

Plants of similar appearance:

References:

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Acknowledgments:

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