Invasive plant species in South Africa

ernstvanjaarsveld
Published on March 5th 2020
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A close up of a cactus
Today we're taking a look at alien invasive plants and how regulations affect our gardens. The regulations divide undesirable plants into three categories - all of them pose a serious threat, but the categories are mainly chosen based on the current utilization of the plants.
Category 1a | Plants in this category must be removed and destroyed. Trade or planting is strictly prohibited.
Category 1b | Plants that must be controlled and wherever possible removed and destroyed. Trade or planting is strictly prohibited.
Category 2 | Plants within this category are potentially invasive, but are commercially important and are allowed to be grown under controlled conditions in demarcated areas and require a permit. However, plants in riparian areas fall within Category 1b.
Category 3 | Plants in this category are plants that may be retained where they already exist, provided they do not have the agricultural resources (vegetation, soil and water), but which may no longer be sold, planted or propagated.
A close up of a flower
Eichhornia crassipes

When is a plant an invader?

An invader can be defined as an alien plant that has the ability to invade undisturbed environment, displace the indigenous plants and change the ecology of the area. Alien plants often come from other countries with a similar climate. The plants were brought in but not their natural enemies. Therefore, they can grow without hindrance, without predators and diseases to keep their numbers in check. In contrast, indigenous plants are in balance with others in their community and the populations' growth and mortality remain more or less the same. There are many other potentially invasive plants that are found in our gardens but have not been incorporated into legislation yet. If necessary, the invasive lists will be revisited and revised in the future.
Psidium guajava

Invaders today a worldwide problem!

Why are invasive plants such a big problem worldwide? Although invasive plants, like all other green plants, perform their normal function of photosynthesis (capturing and converting the sun's energy and also purifying the air of carbon dioxide), they are indirectly a threat to humans. Not only do they threaten natural vegetation or agricultural crops, but our groundwater resources are also adversely affected. Plantations in Mpumalanga, for example, has a major impact on the flow of lowland rivers. Unnecessary energy is spent on their fight that is putting our country and the taxpayer out of pocket.
A close up of a flower
Acacia cyclops

Who is guilty?

As humanity we are guilty and indirectly we all owe a fraction. We are extremely mobile, manipulate our environment wherever we go to our advantage, and plants are transported and planted worldwide. Plants were brought in firstly because of their usefulness to humans (agricultural, ornamental, medicinal, etc.). Some weeds come into a country accidentally, like with horse feed during the Anglo Boer War, and lastly by plant collectors (who gather plants like a seal collector collects seals). The motives of people are often well-meaning, the fruit of mixing the world's plants (without their natural enemies) - a 'fruit salad' results in chaos and headache.
A close up of a lush green field
Acacia cyclops

Category 1 | Declared weeds to be eradicated

Plants in this category include:
- Silver wattle | Acacia dealbata. A category 1 invasive in the Western Cape only and is a category 2 plant in elsewhere in RSA.
- Screw-pod wattle | Acacia implexa
- Long-leaved wattle | Acacia longifolia
- Kangaroo thorn | Acacia paradoxa
- Golden wattle | Acacia pycnantha
- Giant reed | Arundo donax
- Chandelier plant/Mother of millions | Bryophyllum delagoense
- Kanna | Canna indica. The attractive garden cultivars are excluded.
- Queen of the Night | Cereus jamacaru
- Yellow Cestrum | Cestrum aurantiacum
- Purple Cestrum | Cestrum elegans
- Ink-berry | Cestrum laevigatum
- Willow-leaved Jessamine | Cestrum parqui
- Camphor Tree | Cinnamomum camphora. Category 1 only for KwaZulu-Natal, Mpumalanga and Northern Province, but can be planted elsewhere)
- Field Bindweed | Convolvulus arvensis
- Pampas grass | Cortaderia jubata and Cortaderia seloana
- Organ cactus | Echinopsis spachiana
- Bushy Yate | Eucalyptus lehmannii. Only category 1 in the Western Cape and category 2 elsewhere.
- Martin Applecactus | Harrisia martinii
- Red, white, yellow Gingerlily | Hedychium coccineum, Hedychium coronarium, Hedychium flave scens and Hedychium gardnerianum
- Morning-glory | Ipomoea alba, I. indica and I. purpurea
- Lantana spp | All alien seed-forming species
- Coastal tea tree | Leptospermum laevigatum
- River tamarind | Leucaena leucocephala. Only category 1 in the West Cape and Category 2 elsewhere.
- Tree Daisy | Montanoa hibiscifolia
- Oleander | Nerium oleander. Sterile double-flowered cultivars excluded
- Prickly pear | Opuntia ficus-indica. Excluding the thornless.
- Other Prickly pear and related species | Opuntia aurantica, O. exaltata, O. humifusa, O. imbricata, O. lindheimeri, O. monacantha, O. rosea, O. spinulifera & O. stricta.
- Plume albizia | Paraserianthes lophantha
- Bluecrown Passionflower | Passiflora caerulea
- Bananadilla | Passiflora mollissima
- White passionflower | Passiflora subpeltata
- Fountain grass | Pennisetum setaceum
- Australian cheesewood | Pittosporum undulatum
- Water lettuce | Pistia stratioiotes
- Durban guava | Psidium × durbanensis ined
- Wax tree | Rhus succedanea
- Sweet brier | Rosa rubiginosa and Rubus cuneifolius
- Brazil pepper | Schinus terebinthifolius. Only category 1 in KwaZulu-Natal, 3, in the rest of RSA.
- Red sesbania | Sesbasnia punicea
- Spanish broom | Spartium junceum
- Yellow bells | Tecoma stans
Learn more about these invasive plants in the plant profiles below:
A large tree

Category 2 | Invasive plants with economic and other potential

These plants may be cultivated in certain demarcated areas and measures must be taken to prevent them from spreading. The regulations are not clear here and may also include some urban areas where pre-existing trees can be preserved. Plants in this category may only be sold by certain nurseries if the buyer has obtained permission to plant that plant in a delimited area. It is in this and especially the last category where many useful and ornamental plants are found and will affect us the most. The second category usually consists of useful plants such as forestry species, firewood, windbreaks, shade, soil stabilization or animal feed and then the guava tree.
Plants in this category include:
- Coastal wattle | Acacia cyclops
- Black wattle | Acacia mearnsii
- Australian blackwood | Acacia melanoxylon
- Port Jackson | Acacia saligna
- Sisal | Agave sisalana
- Old man saltbush | Atriplex nummularia
- River oak | Casuarina cunninghamiana
- Australian pine tree | Casuarina equisetifolia
- River red gum | Eucalyptus camaldulensis
- Sugar gum | Eucalyptus cladocalyx
- Karri | Eucalyptus diversicolor
- Bushy Yate | Eucalyptus lehmannii
- Grey ironbark | Eucalyptus paniculatalox
- Honey locust | Gleditsia triacanthos
- St. John's wort | Hypericum perforatum
- Aleppo pine | Pinus halepensis
- Patula pine | Pinus patula
- Maritime pine | Pinus pinaster
- Radiata pine | Pinus radiata
- Chir pine | Pinus roxburghii
- Loblolly pine | Pinus taeda
- Honey mesquite | Prosopis glandulosa
- Northern Red Oak | Pinus velutina
- Guava | Psidium guajava
- White popular | Populus alba
- Pale poplar | Populus × canescens
- Great watercress | Rorippa nasturtium-aquaticum
- European blackberry | Rubus fruticosus
- Weeping willow | Salix babylonica
- Brittle willow | Salix fragilis
- Johnson grass | Sorghum halepense
Learn more about these invasive plants in the plant profiles below:
A white plate topped with different types of fruit

Category 3 | Famous garden plants that are Category 3 invaders

Plants in this category may be retained where they are already growing, provided all reasonable measures are taken to prevent them from spreading. However, where they threaten natural resources, they must be eradicated. They may also no longer be sold by nurseries or planted in the future. This category includes many ornamental shrubs and trees.
- Cootamundra wattle | Acacia baileyana
- Pepper tree wattle | Acacia elata
- Pearl Acacia | Acacia podalyriifolia
- Tree of heaven | Ailanthus altissima
- Lindley's saltbush | Atriplex lindleyi
- Purple butterfly tree | Bauhinia purpurea
- Mountain ebony | Bauhinia variegata
- Silverleaf Cotoneaster | Cotoneaster pannosus
- Lukwart | Eriobotrya japonica
- Silky oak | Grevilia rubusta
- Morning-glory | Ipomoea purpurea
- Jakaranda | Jacaranda mimosifolia
- Japanese privet | Ligustrum japonicum
- Chinese privet | Ligustrum lucidum var ovalifolium
- Chinese privet | Ligustrum sinense
- Common privet | Ligustrum vulgare
- Trumpet lilies | Lilium formosanum = L. longiflorum
- Chinaberry | Melia azedarach
- Sentang | Azadirachta excelsa
- Giant sensitive tree | Mimosa pigra
- White Mulberry | Morus alba
- Manatoka | Myoporum tenuifolium
- Boston fern | Nephrolepis exaltata
- Bella Sombra | Phytolacca dioica
- Woolly Plectranthus | Plectranthus comosus
- Brazilian guava | Psidium guineense
- Strawberry guava | Psidium cattleianum
- Orange fire thorn | Pyracantha angustifolia
- Nepal firethorn | Pyracantha crenulata
- Rambling cassia | Senna bicapsularis
- Peanut Cassia | Senna didymobotrya
- Brazil pepper | Schinus terebinthifolius
- Malabar plum | Syzygium cumini
- Salt cedar | Tamarix ramosissima
- Tipuana | Tipuana tipu
- Toon tree | Toona ciliata
Learn more about these invasive plants in the plant profiles below:
A close up of a flower
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