Know Your Invasive Species

This issue looks at the blue-leaf cactus, the bramble, and other alien plant species that require eradication.

According to the Biodiversity Act No. 10 of 2004, landowners are under legal obligation to control invasive alien plants. They must identify all invasive alien plants on their properties and use the correct methods to control or remove them.

Blue-leaf cactus (Opuntia robusta)

This upright, succulent shrub grows 1m to 4m tall and has stems consisting of a series of flattened, fleshy cladodes (segments). It flowers mainly during late spring and summer. The flowers are 5cm to 8cm in diameter and yellow in colour, occasionally with reddish streaks on the outer petals.

The immature fruits are green, but turn pinkish to purplish as they mature. The mature fruits (7cm to 8cm long and 6cm in diameter) are fleshy, barrel-shaped or rounded (globose), with tufts of tiny barbed bristles on the surface.

The dark red pulp in the centre of the fruit contains a large number of light or dark brown seeds, each 3mm to 5mm across.

Cladode fragments are spread by becoming attached to animals, shoes and vehicles, or being dumped as garden waste. The fruit is eaten by various animals and birds, which spread the seeds in their droppings.

The cactus is an environmental weed, infesting pastures, granite outcrops and open woodlands.