Few people know that South Africa is the country with the third richest plant diversity in the world; the other two being two rain forests (Brazil and Indonesia). This is highly significant, given the fact that it is a water-stressed country. South Africa has many different biomes and vegetation types and unique plants species, which can be found nowhere else on earth.

Argemone ochroleuca (white­-flowered Mexican poppy / witblom bloudissel)
Photo: Petro Lemmer

The Bronberger’s distribution area is home to a rich plant diversity which can still be found in nature reserves in and around Pretoria, such as the Faerie Glen Nature Reserve (part of the Bronberg mountain bushveld critically endangered ecosystem), Moreletakloof Nature Reserve, Groenkloof Nature Reserve, Rietvlei Nature Reserve, Wonderboom Nature Reserve (part of protected Magalies mountain range) and many other natural areas including conservancies and private nature reserves. 

Mirabilis jalapa (four-­o’clock / vier­ uurtjie)
Photo: Petro Lemmer

Alien invasive plant species, of which more than 350 species are known to occur in Gauteng alone, are the biggest threats to these nature areas and garden escapees are the biggest culprits. In their native countries these plants are naturally controlled by insects, fungi and other biological agents to prevent them taking over their natural habitat. But, in other countries these natural control agents do not occur and the exotic plants are free to grow wherever they find suitable habitat.

More than half of all alien and invasive plant species listed in South Africa found its way into the country by means of the horticultural industry, such as ornamental garden and pot plants. Homeowners, gardeners and plant collectors can make a big difference by ensuring their gardens are free from these alien invasive plant species and in so doing also prevent their property value decreasing.

Datura stramonium (common thorn apple / gewone stinkblaar)
Photo: Louise Kritzinger

Many pretty weeds along the roadsides, such as Mexican thistle, Thorn apple (malpitte), Smelter’s bush and Four o’clock, all started their abode in our country as colourful garden ornamentals. Some pretty climbing plants, infesting suburbs and nature areas, were likewise introduced.

Plant collectors and home gardeners are inadvertently guilty of allowing their plants to escape, particularly fruit-bearing plants such as cactus (most cactus species are alien invaders), mulberry, guava, prickly pear, where birds have access to the fruit of the plants. Other ornamental creepers, such as cat’s claw, disperse their feather-light seeds into the wind once the pods open. 

Dolichandra unguis­-cati (cat’s claw creeper / katteklouranker)
Photo: Louise Kritzinger

This is the first of a series of articles on alien and invasive plants in the Bronberg area to inform and educate landowners of the different alien invasive plants, their impact and the law compelling all land owners to take action against them.

Visit www.invasives.org.za for more information on alien and invasive plant and animal species. 

This article was sponsored by the Friends of the Faerie Glen Nature Reserve.