Pretoria National Botanical Garden

One of the greatest assets of the Pretoria National Botanical Garden is its natural grassland. Although the grassland area was disturbed by agricultural activities more than fifty years ago, it has recovered well by going through the natural succession process. It has reached a natural climax that is typical of the Bankenveld, with a diverse mixture of wild flowers, climax grasses such as Red Grass, Themeda triandra, and Thatch Grass, Hyparrhenia hirta, and most of the biodiversity associated with a grassland ecosystem. The Bankenveld (Acocks 1988) is a transition area between the Cold Highland Grasslands of the Highveld and the Bushveld Savanna of Africa.

The Pretoria National Botanical Garden was formerly part of the agricultural research and experimental section of the University of Pretoria. After many negotiations, this piece of land was handed over to the Department of Agriculture in 1946 for an arboretum or botanical garden, where trees and other plants could be planted for research purposes. Many trees were planted, but the open, sunny, grassy areas to the southeast of the garden were kept untouched for experiments, such as burning programmes. Today, this relatively pristine grassland forms part of a most valuable mini-nature reserve, just east of the Silverton Ridge.

Unfortunately, the grassland has been cut off from the wetland area, opposite the Council for Scientific and Industrial Research to the east, by roads and a busy highway. The grassland is home to various small mammals like rabbits, golden mongoose, hedgehogs, and even duiker. Birds typical of the Highveld grasslands, such as plover and guinea fowl, are abundant.

As in any typical grassland, various bulbs and orchids occur: Albuca setosa, Boophone disticha, Eulophia clavicornis, E. ovalis subsp. ovalis, Hypoxis hemerocallidea, and H. rigidula.

Wild flowers pop up after winter, even before the first spring rains have fallen and they all produce seed, even the wild orchids, which is very useful for regeneration and research purposes. These wild flowers are not so dependent on the rain as some of the grasses, as they store their nutrients in modified underground organs to survive unfavourable times like winter or drought. They include Callilepis leptophylla, Castalis spectabilis, Clerodendrum triphyllum, Elephantorrhiza burkei, Indigofera sordida, Ipomoea crassipes, and Sphenostylis angustifolia.

There are even some endemic and rare species, for example, Hemizygia pretoriae, that are only found around Pretoria.

A fascinating member of the family Asclepiadaceae, Pachycarpus schinzianus is also of great medicinal value and has fortunately managed to survive here in the garden, whereas in the wild they have disappeared rapidly like many other medicinal plants. Other valuable medicinal plants that grow here are Artemisia afra, Asclepias species, Boophone disticha, Dicoma zeyheri, Elephantorrhiza elephantina, Felicia muricata, Gazania krebsiana, Hypoxis hemerocallidea, Lippia javanica, Monsonia attenuata, Pollichia campestris, Scabiosa columbaria, Scilla nervosa, Teucrium trifidum, and Vernonia oligocephala.

The Haworthia-like highveld bulbous plant, Chortolirion angolense, also occurs here.

Important Bankenveld species, such as Triumfetta sonderi and Triaspis hyperi coides, have disappeared totally from the grassland, and others, such as Clematopsis scabiosifolia, Boophone disticha, and Chocolate Bells, Trichodesma physaloides, with its brown and white flowers, are disappearing. The Ink Flower, Cycnium adonense, appears in spring, giving a delightful display of a profusion of white flowers. There is still some Travellers’ Joy, Clematis brachiata, which attracts many insects to an abundance of pollen and fragrant flowers. Then there is Kohautia amatymbica, a nocturnal plant that fills the air with a delectable scent at night. Various Helichrysum and Senecio species are found all over the grassland.

In more open areas with less dense vegetation, flat-growing copper-coloured Hermannia depressa grow. There is a very close association between the copper butterflies, which feed only on these plants, and ants: the ants take the pupae of these butterflies to their nests where they remain until the adult emerges from the pupa.

Towards the rocky hill, the following plants occur: Aloe transvaalensis, Rothmannia capensis, Ochna pulchra, Canthium mundianum, Nuxia floribunda, and Xerophyta retinervis.

There is a mixture of shrubs and mostly small trees on the ridge. Most of the shrubs have delicious, edible fruit: Ximenia (Sour Plum), Englerophytum magalismontanum (Milk Plum), and Vangueria infausta.

The creeper, Ancylobotrys capensis (Wild Apricot), is also found amongst the rocks, producing orange-coloured, velvety round fruit in summer. Close to this rocky hill area, a delicate lilacpink flowering herb, Cleome maculata (also known as Pretty Lady), is found. During the last ten years, taller grasses have been taking over, owing to management practices in winter and good rains during the growing season. Hillsides and wetlands should not be separated from the grassland, as all form integrated parts of the whole Bankenveld ecosystem. If split up or mismanaged, the species diversity will decline unavoidably, not only of plants, but also of all the other living creatures forming the network of life within the grassland. With fewer wild flowers, there will be fewer insects attracting fewer birds and fewer mammals, so that in the end the grassland starts to degenerate into an area of unpalatable, tall, or spiny grasses.

Fortunately, the natural grassland of the Pretoria Garden is being preserved with sensitivity and it is still a safe haven for many indigenous birds, small mammals, and many insects.

A view across the garden in spring.

—by Priscilla Swartz

SABONET News 7.3: 205

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ACOCKS, J.P.H. 1988. Veld types of South Africa, 3rd edn. Memoirs of the Botanical Survey of South Africa No. 57. Botanical Research Institute, Pretoria.