Twitter Facebook

Water hyacinth

Water hyacinth (Pontederia crassipes) is South Africa’s most serious aquatic invader. Previously known as Eichhornia crassipes it is now in the genus Pontederia. Fortunately, several highly effective biocontrol agents have been released to combat the rapid growth and spread of this plant. The Centre for Biological Control at Rhodes University have released over 300 000 plant hoppers (Megamelus scutellaris) onto water hyacinth in Hartebeespoort Dam, which as greatly reduced the density.

Water hyacinth thrives in nutrient rich polluted water systems including rivers, dams, and lakes. It is an ongoing problem across many water bodies, especially in summer when this floating herb can double its growth rate every two weeks.

Download

Tall Verbena

One of three Category 1b invasive plants, purple-top (Verbena bonariensis) is also called tall verbena. It is a common and widely distributed weed that infiltrates grasslands and wetlands. It is a problem in nature reserves and national parks where the seeds are easily spread. It is unpalatable to many indigenous grazing mammals. The purple clustered flowers are prominent in late summer and early autumn.

Download

Tree of heaven

Native to China, the Tree of Heaven (Ailanthus altissima), is an alien invasive tree in South Africa.

It is a common urban invader and generally occupies disturbed areas. Its leaves, flowers and seeds are present during spring and summer. Leaves have a characteristic notch at the base of each leaf and leaves emit a distinctive smell when crushed.

Lyriche Drude from the University of the Witwatersrand is undertaking a study on the distribution of this species. You can assist with this project by providing locality information to the following platforms. If seen at any locality (e.g., roadside or garden), please collect the following:

  • Exact (GPS) location
  • Picture of plant (if possible)
  • Send information to Lyriche Drude at wits@gmail.com

OR

Download

Tickseed

The daisy family has many invasive species including the notorious pompom weed. Another invasive flower of grasslands is the tickseed which comes from the eastern parts of the United States. Like other members of this group, they produce copious numbers of seeds which are easily spread via wind and water.

Download

Spear thistle

A familiar garden and agricultural weed which dominates in some areas during late summer. Spear thistle invades roadsides, seepage zones, grassland and agricultural fields. The leaves are spiky and hairy and therefore unpalatable to livestock and grazing game animals. It can also cause skin irritations to people coming in contact with this weed.

Download

Red sunflower

The red sunflower (Tithonia rotundifolia) flowers from February through to July. It can be abundant along road verges but also penetrates seepage zones and wetlands. It is an annual herb with a rapid growth rate. Although called the red sunflower, the petals are more of a bright orange-red. These images were taken alongside the freeway leading into Pretoria with the iconic UNISA building in the background. Red sunflower is found across Gauteng, Limpopo, Mpumalanga and KwaZulu-Natal.

Download

Red Sesbania

This is a deciduous shrub or small tree reaching 4 metres high. It produces orange or red flowers in late summer and four-winged, elongated seed pods. The seeds are reportedly poisonous to indigenous birds. It is highly invasive along streams and rivers, growing along banks, as well as roadsides and drainage lines in high rainfall regions.

Download

Pompom weed

Our grasslands are under threat from invasive Category 1b pompom weed. This noxious plant overtakes grasslands and outcompetes indigenous grasses and shrubs. People are often tempted to cut the flowers for floral decorations, but this plant must not be transported. By law, pompom weed must be controlled if found growing on your property.

Download

Peanut butter cassia

This shrub which is naturally found in tropical Africa has established across eastern and southern Africa. Despite the common name, the seeds and flowers are poisonous and toxic to livestock. It invades coastal bush, grassland and savanna, particularly in the warmer climates.

Download

Drooping prickly pear

Numerous cacti have become highly invasive in South Africa. The drooping prickly pear or cochineal prickly pear (Opuntia monacantha) thrives in the more wet and humid lowlands of KwaZulu-Natal and the Eastern Cape. It is often seen along beachfront embankments.

A cochineal called Dactylopius ceylonicus is host specific and highly effective as a biocontrol agent. It greatly reduces the density of cacti. The Centre for Biological Control based at Rhodes University in Makhanda in the Eastern Cape is at the forefront of biological control for invasive cacti.

Download

© Copyright 2021 Invasives SA

Twitter Facebook