All alien invasive species are pests and should be removed because of their invasive status and damage to the environment, but there are two indigenous plants that I would like to ban from all gardens and garden centres; Asystasia gangetica and Strelitzia nicolai.
What nobody tells you is that these plants spread at an alarming rate. They are popping up all over my garden, sun or shade, dry or damp areas. Starlings and doves feed on the Strelitzia seeds and that will account for the spread in and around Knysna. How the Asystasia arrived in my garden, and how the seeds are dispersed, I don’t know.
Asystasia gangetica: Creeping foxglove, is widely distributed along the eastern coastal areas of the country. It is recorded in the Eastern Cape, Kwa-Zulu-Natal, Swaziland, Limpopo, Mpumalanga, Botswana and Namibia, and also occurs in tropical Asia. It is an attractive, fast-growing, spreading, herbaceous groundcover that grows from 300mm to 600mm in height. It bears attractive cream-coloured flowers with tessellated purple markings on the lower petal of the corolla in spring and summer. Flowers are produced over a long period and followed by capsules with brown seeds. The stems root easily at the nodes, and this ability to reproduce by vegetative propagation results in it smothering surrounding vegetation with its herbaceous layer. It has become a popular plant for covering Sholin walls and as groundcovers for shady areas. According to the Global Invasive Species Database this plant has caused major problems in the ecosystems of the Pacific Islands and is potentially highly invasive.
Strelitzia nicolai – the Natal wild banana grows mostly in coastal dune vegetation and in evergreen forests near the coast. It is a common feature of coastal vegetation from East London northwards towards Mozambique. The Natal wild banana grows up to 12m high and 4 m wide! It may be attractive to some gardeners, but I find no beauty in the clustered tattered leaves, nor the flowers that are obscured in the black sheath.
The fleshy roots grow rapidly into a huge root ball which can exert tremendous pressure on walls, paving, swimming pool walls and house foundations – not unlike another ‘form’ plant favoured by some landscapers, the Kiepersol (Cussonia spicata) which has an equally destructive root system. If you really have to plant strelitzias or kiepersols, do so at a distance, and I mean a very fair distance away from drains, paving, pools or homes. Knysna gardens are generally small, and not suited to these two species.