Common Prickly Pear

Opuntia stricta (Haw.) Haw.

Synonyms - Opuntia inermis, Cactus strictus

Family: Cactaceae.

Names:

Opuntia is Latin of uncertain relevance but may refer to the town of Opus.
Stricta is from the Latin strictus meaning upright or drawn together and refers to the upright growth habit.
Prickly pear - refers to the prickly nature and the pear shaped fruit.

Other names:

Araluen Pear an intermediate variety between var. stricta and var. dillenii in NSW.
Common Pest Pear for var. stricta in NSW and QLD.
Erect Prickly Pear
Gayndah Pear (QLD)
Pest Pear
Spiny Pest Pear for var. dellinii.
Spiny Prickly Pear

Summary:

Erect, perennial shrub growing 1 to 3 m tall. Green, succulent, flattened stems with scattered warts (areoles) and bright yellow flowers about 60 mm diameter in spring that form red, fleshy, edible fruit about 50 mm long. Occasionally it has a few spines from each "wart".

Description:

Cotyledons:

Two.

Leaves:

Several, purplish to pink, conical and scale like, 5-7 mm long, sometimes very small, below the 'warts' on young stems. They fall off with age.

Stems:

Erect, up to 3000 mm tall and usually 1000 mm tall, made up of oval to egg-shaped, flattened, spiny. dull green to blue-green, fleshy segments 100-250 mm long x 70-160 mm wide and 10-20 mm thick. Branches from near the ground with no definite trunk and forms large clumps. Hairless. Has 'warts' or areoles, 12-100 mm diameter, in the leaf axils, 35-50 mm apart in 2-3 diagonal lines, sometimes, with tufts of finely barbed, yellow bristles and may have 1-11, slightly curved, spines 20-60 mm long or spineless. Each 'wart' may produce a flower, new stem segment or roots.

Flower head:

Usually several flowers on the edges of the stem segments.

Flowers:

Pale yellow, no stalk. Floral tube narrowly egg-shaped, 50-65 mm long.
Ovary - One style, yellow. Several stigmas.
Sepals - Difficult to distinguish from the petals.
Petals - Many, overlapping, yellow with green or pink markings on the back, 60-80 mm wide when fully open. Outer lobes, sepal like, abruptly pointed on the tip. Middle lobes kidney shaped and abruptly pointed or triangular or with a point where the midrib projects. Innermost 8-10 lobes petal like, yellow, egg-shaped or cut off at top. More correctly termed petaloids.
Stamens - Many.
Anthers - Yellow.

Fruit:

Pear shaped to globular berry, red purple when ripe with red flesh, 38-75 mm long x 25-40 mm wide, with a circular depression or flat at the top. Has warts with fine barbed bristles.

Seeds:

Many, smooth, yellow to light brown or black, hard coated, globular seeds about 5 mm wide in the pulp in the middle of the fruit.

Roots:

Fibrous. Shallow.

Key Characters:

Flat egg shaped phylloclades(stem segments) with 3 rows of areoles. Yellow flowers.

Biology:

Life cycle:

Perennial. Seed germinates at any time of the year, producing a delicate bristly seedling that normally dies. Survivors grow slowly and make new segments on the edges of their small stem segments. After 3 years they may flower. Plants are very long lived and most new plants arise from stem segments that fall to the ground or are broken off. Roots form from the areoles (warts) in contact with the soil and new stem segments are produced from the areoles on top. Segments are often broken off and carried by floods.

Physiology:

Drought tolerant.
Crassulacean acid metabolism (CAM) plant helps preserve water.
Detached stem segments can remain viable indoors for 3 years.

Reproduction:

By seed and stem fragments.

Flowering times:

November in western NSW.
September to October in Perth.
Spring and early summer in WA.

Seed Biology and Germination:

Seed may remain viable for 20 years.

Vegetative Propagules:

Stem segments.

Hybrids:

Several varieties. Var. stricta has 0-1 spines, 20-40 mm long on the areoles. Var. dillenii has up to 11 spines, 10-60 mm long. Other varieties have no spines.

Allelopathy:

Population Dynamics and Dispersal:

Seed passes through birds and foxes in a viable condition and is spread in the droppings.
Local spread is mainly due to stem fragments taking root after being broken from the mother plant by animals, wind or flood waters. Small segments of the fruit may attach to passing animals and vehicles to be spread more widely.
Long distance spread is usually by intentional planting.

Origin and History:

Eastern tropical coast of America, West Indies and Bermuda.
In NSW by 1839 as a pot plant in Scone.
Probably introduced as a garden plant or to feed cochineal insects.
It had infested 23.5 million hectares by 1920. Cactoblastis moths were introduced in 1926 and 1932 and the caterpillars of this moth provided control over most of the densest infestations by 1935. In Boonarga in southern Queensland a hall was built to honour the caterpillar and may be the only monument dedicated to an insect in the world.

Distribution:

NSW, NT, QLD, SA, VIC, WA.
One million hectares is still infested in cooler areas where bio control agents are not effective. Prickly Pear is very poorly mapped in WA an many other areas.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Grows in tropical regions through to semi-arid savannas. Semi arid, warm temperate, subtropical and tropical regions.
The most severe infestations occurred in the 500-750 mm rainfall zone in Australia.

Soil:

Red earths.

Plant Associations:

Bimble box and white cypress pine communities. Brigalow scrub. Savannas.

Significance:

It 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:

Edible fruit, but require careful handling to avoid the irritating bristles. Fruit used for jams and jellies. Stem segments can be candied to form a chewy sweet. Young segments can be boiled and eaten as a green vegetable. In all cases the bristles must be singed with flame then the eyes sliced out.
Planted as a hedge.
Used in herbal remedies for whooping cough and diabetes.
Eaten by stock during droughts.
Honey plant.
Spines used as gramophone needles.

Detrimental:

Takes over areas excluding most other species.
Sharp spines cause injury to stock especially the tongue and facial areas.
The fruits are breeding grounds for fruit fly.
Harbour vermin such as rabbits.
Form dense inpenetrable patches.

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:

Noxious weed of NSW, QLD, SA, NT and WA.

Management and Control:

Stem fragments readily root making cultivation ineffective.

Thresholds:

Very low in susceptible areas.

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.
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.
Small quantities of collected material may be killed by deep freezing at -200C for 48 hours.

Herbicide resistance:

Biological Control:

Controlled by the cactoblastis caterpillar and cochineal beetle and other introduced insects by 1935. The cactoblastis caterpillar is orange with black spots and a black head and tunnels into the stem segments reducing the plant to a rotting mass.

Related plants:

Devil's Rope (Opuntia imbricata)
Drooping Prickly Pear (Opuntia vulgaris)
Indian Fig (Opuntia ficus-indica)
Tiger Pear (Opuntia aurantiaca) is lower, more branched and much more spiny.
Velvet Tree Pear (Opuntia tomentosa)
Wheel Cactus (Opuntia robusta)
White-spined Prickly Pear (Opuntia streptacantha)
(Opuntia cochenillifera)
(Opuntia cylindrica)
(Opuntia dejecta)
(Opuntia elatior)
(Opuntia humifusa)
(Opuntia lindheimeri)
(Opuntia microdasys)
(Opuntia parguayensis)
(Opuntia subulata)
(Opuntia sulphurea)

Plants of similar appearance:

Cacti.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P140. Photo.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P345.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P503. Photo.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P122. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #907.15.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P80.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P113-116. Diagram. Photo.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P364-366. Photos.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.