Beautiful but Invasive.

Posted by on September 27, 2017

Contributor: Leonie Twentyman Jones

Once upon a time, many years ago, a young man arrived in Cape Town to run an apothecary shop for a physician. He was ambitious and worked hard, and then married a wealthy widow who owned a lucrative tobacconist shop in what is now St George’s Street – a most desirable address and business. Their business prospered and the now not so young man, Carl Ludwig, had the leisure time and interest to become involved in the intellectual life of Cape Town. His favourite interest was collecting plants as well as birds and insects, which he sent to Stuttgart, in his home country. He then purchased three acres of ground in what is now Tamboers Kloof in Cape Town, where he established a garden. He collected local indigenous species, (incidentally becoming friendly with George Rex during his collecting trips to the Eastern Cape) exchanged plants and seeds with Kew Gardens, and also imported over 1,600 plants and trees from other countries. Two of the trees imported from South America, to great acclaim at the time because of their beauty and delightful scent, have nearly 200 years later become problematic. And yet today when it is suggested that they should be removed, the excuse is ‘Oh but their flowers are so beautiful!’ or; ‘But, they have such a gorgeous scent!’

You may have guessed that one of the trees was the stunning Jacaranda mimosifolia, one of our best loved street trees, particularly in Pretoria, with its spectacular mauvish-blue flowers. This tree is now listed as an invasive alien as it competes with and replaces indigenous trees and when planted near rivers is likely to impact on the flow of water in our seriously parched land. It is a particular problem in the northern provinces and must be controlled if growing near rivers and certainly no new trees should be planted. A beautiful indigenous alternative is the deciduous Tree wisteria or Bolusanthus speciosus which also has blue-mauve, fragrant, pea-like flowers in spring and early summer. The Tree wisteria has a non-invasive root system and doesn’t get too big for a medium or small garden.

Jacaranda mimosifolia

Cestrum nocturnum

The other problem tree introduced by Carl Ludwig is the Cestrum nocturnum or Queen of the Night. Its only redeeming feature is the scent of its night-time blooming flowers. Its seeds are easily spread by birds and water and the plants grow quickly – invading the fringes of large gardens, suburban verges, rural lands and coastal forests. All parts of the trees are poisonous and in rural areas it has become a major problem as it is poisonous to livestock particularly cattle.  It has a deep and persistent tap root which inhibits its removal. Having recently seen how quickly these trees are invading the coastal forests in Transkei, I am concerned about its possible impact on our Knysna forests. You only have to walk round Leisure Isle on a hot summer evening to realise how many Cestrums are flourishing here. For those of you who are addicted to the scent of the Cestrum, why not trying planting indigenous trees with a lovely scent? For example the Wild gardenia (Rothmannia capensis), September bells (Rothmannia globosa) or the White gardenia (Gardenia thunbergia) all have fragrant flowers.

Leonie Twentyman Jones

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