African Wildlife & Environment Issue 82

GARDENING FOR BIODIVERSITY

there is also a white-flowered variety. It has invaded forest edges, hillsides, riverbanks, woodlands and urban open spaces in our northern provinces. Many countries have taken action against this invader and, on the other side of the globe in Hawaii, D. erecta has been listed as one of their worst invasive horticultural plants. This multi stemmed, often rambling, shrub or small tree, which started life both there and in South Africa as a garden ornamental and hedge plant, hails from tropical America. Unfortunately it is still widely cultivated here despite being so poisonous that children have died after eating the berries. Birds are not affected by the poison and exacerbate the environmental problem by spreading the seeds. Two other problematic invasive alien plants with blue flowers are Blueweed Ageratum conyzoides , also known as Billy-goat Weed, and the Mexican Ageratum A. houstonianum , also known as Garden Ageratum or Bluemink. Both these closely related herbaceous species have a totally different form to P. auriculata and, although usually blue or mauve, the flowers can vary from pinkish to white. Introduced from the Americas and West Indies, these plants have now spread from the Limpopo Province to the Eastern Cape with foot-holds in the Western Cape and North West Province. With their windblown seeds, they have invaded our forests, grasslands, riverbanks, wetlands and cultivated areas. Besides being poisonous, harbouring them is illegal. Like so many of our problem plants these soft, hairy, annuals are garden escapees which were originally cultivated as ornamentals because of the attractive, fluffy flower-heads. One of the alternative common names of A. houstonianum , ‘Todd’s Curse’, is in ‘honour’ of a 19th century Pietermaritzburg nurseryman. One can only wonder how many more of our exotic garden plants, currently considered harmless, will become a

Agamas are addicted to bees and other insects that frequent Plumbago auriculata

Fruit of the nasty alien invader plant Duranta erecta (Photograph: W Menne)

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