PlantLife Volume 60.4, December 2025. Exploring the flora of the Oribi area in southern KwaZulu-Natal

 

Exploring the flora of the Oribi area in southern KwaZulu-Natal

by Kate Grieve. Photos by G Grieve

Phylica natalensis (Vulnerable)

Just inland of Port Shepstone in KwaZulu-Natal, the area known as Oribi covers different vegetation types and a wide variety of habitats that provide endless opportunities for botanical exploration and discovery.

Maerua rosmarinoides (LC)

The Oribi Gorge Nature Reserve is known for its outstanding natural beauty and biodiversity. The steep sides of the Mzimkulwana river gorge are dominated by Pondoland scarp forest and provide different habitats, from forest shade to cliff face. Your encounters can vary from a grove of graceful old Heywoodia lucens over 10 m tall to the scrambling stems of Capparis tomentosa with its profusion of spidery flowers.  On the forest floor you can find Crinum moorei (VU) and Plectranthus oertendahlii (Rare), while P. oribiensis (Rare) appears along the forest margin. Gymnosporia bachmannii (VU) grows on the river bank and Encephalartos natalensis (CR) can be seen clinging to the cliffs.  In contrast, the Mzimkulu river valley to the north is wider, the banks slope gradually upwards to the cliff tops and much of the vegetation is more characteristic of valley bushveld.  Consequently, there are many differences in species between the two gorges. On one farm road into the Mzimkulu River gorge we found five different Strychnos species – S. decussata, S. gerrardii, S. henningsii, S. spinosa and S. usambarensis.

Apodytes abbottii(Near Threatened)

Aspalathus abbottii (Vulnerable)

Although the surrounding areas of Oribi flats and Paddock have been transformed largely by agriculture, they also host a surprising variety of remnant habitats for indigenous plants and consequently, considerable botanical diversity. Oribi flats refers to an area that lies on a plateau between two forested gorges, deeply incised by the Mzimkulu and Mzimkulwana rivers. The Paddock area is bordered by the Oribi gorge nature reserve on one side and the Vungu River in the south. The underlying geological substrate of most of the area is Msikaba Formation sandstone, characteristic of the Pondoland-Ugu Coastal Sandstone Sourveld vegetation type that occurs along the eastern seaboard of South Africa between Port St John’s and Port Shepstone. This region is referred to as the Pondoland Centre (PC), a biogeographical region of remarkable floral diversity and endemism, and the Oribi area lies at its northeastern boundary.  It is therefore no surprise that the grasslands and forested gorges here host many special plant species, approximately 60 of them being endemic to the Pondoland Centre and at least half of those being of conservation concern (see Table X). There are also adjacent sections of valley bushveld and ngongoni grassland, providing additional habitats for plant diversity.

Brachystelma tenellum (Vulnerable)

Cadaba natalensis ( LC)

Despite the predominance of land transformed by agriculture, there are remnant patches of grassland between crop lands and along strips adjacent to the cliff edges. The conservation of these small sections of grassland is in the hands of private farmers who treasure the floral richness and diversity on their properties. There are also small grassland patches formally protected in the Oribi Gorge and Mbumbazi Nature Reserves.

For several years we have monitored two strips of grassland above the river gorges on either side of Oribi flats, one on the northern bank of the Mzimkulwana River, and the other on the southern bank of the Mzimkulu River. Both strips are rocky and provide sheltered habitats for Orchidaceae and Gesneriaceae, amongst others. Many of the endemic species in Table X were recorded in these strips. Below the cliff edges, rock ledges provide niches for trees to grow and their shade creates ideal habitats for interesting forbs, such as Caputia oribiensis (CR), Crassula sarmentosa var. integrifolia (Rare), Gasteria croucheri (VU) and Plectranthus ernstii (NT).

Caputia oribiensis (Critically Rare)

Plectranthus ernstii (Near Threatened)

There are also some unusual, although not threatened, trees in the forest margins on the cliff edges, such as Seemannaralia gerrardii and Cadaba natalensis, the latter with its delicate whiskery flowers. The rocky grasslands provide suitable habitat for Aspalathus abbottii (VU), known only from three sites in this area.  Looking closely at the rock sheets you can find Crassula obovata var. dregeana (VU), the diminutive Ceropegia tenella (VU) as well as Delosperma subpetiolatum (VU) and the ephemeral magenta flowers of Anacampseros rufescens (LC). In spring the remnant grasslands between the cane fields are covered in flowers, including Lotononis bachmanniana (NT), Tephrosia bachmannii (VU) and several Indigofera species. At the right time of year, Turraea pulchella (VU) can be found peeking out from the surrounding vegetation.

Crassula obovata subsp. dregei (Vulnerable)

Lotononis bachmanniana (Near Threatened)

  

Tephrosia bachmannii (Vulnerable)

 

Turraea pulchella (Vulnerable)

Some interesting and special plants can be found in the grassland at Lake Eland, a few kilometers westward. There is an outlier subpopulation of the narrow-leaved Callilepis leptophylla (LC) and one of the few known subpopulations of the newly described Indigofera hydra (NE).

During the CREW/iNaturalist bioblitz in April, we visited a farm in Paddock where a narrow strip of grassland overlooking the Vungu River has been conserved. It is home to many of the flowering plants associated with the PC. Although there is a great deal of similarity in the forbs that occur at the cliff edges at Paddock and Oribi flats, there are some interesting differences. Paddock hosts the seldom seen and northernmost subpopulations of Phylica natalensis (VU) and Leucospermum innovans (EN), as well as Leucadendron spissifolium subsp. oribinum (VU) while these taxa have not been observed at Oribi flats, just a few kilometres away.  On the forest margins and cliff edges we found Apodytes abbottii (NT), Canthium vanwykii (NT), Cryptocarya wyliei (NT), Eugenia erythrophylla (NT), Grewia pondoensis (NT), Putterlickia retrospinosa (NT) and Rhynchocalyx lawsonioides (NT).

Leucospermum innovans (Endangered)

Leucadendron spissifolium subsp. oribinum (Vulnerable)

Eugenia erythrophylla (Near Threatened)

Rhynchocalyx lawsonoides (Near Threatened)

Streptocarpus trabeculatus (LC)

Outside private properties and nature reserves, the survival of these special grassland plants is threatened by the invasion of alien species, overgrazing and uncontrolled fires.

Fire is an important factor for maintaining diversity in grasslands.  Without fire, grass species become moribund and restrict the light and nutrients that other herbaceous plants need to survive and reproduce. While there is agreement that the fire regime needs to be well managed, there is sometimes lack of consensus about the optimal frequency. Fire stimulates growth and flowering and in the temperate and subtropical coastal region of KZN, the grasslands can respond well to burning every second year, in the absence of extenuating factors like excessive livestock grazing or drought conditions.

Indigofera hydra (Not evaluated)

Searsia acocksii (Near Threatened)

With the help of a conservation-minded farmer, we explored the impact on herbaceous plants of burning grasslands every second year at Oribi flats. Two undisturbed grassland patches were identified, approximately 4 and 3 ha respectively, separated by a natural drainage line and adjacent to cane lands.  Apart from a few differences, the patches were comparable overall in terms of common flowering plants for the area, including grasses. Genera such as Acalypha, Crassula, Euphorbia, Hilliardiella, Helichrysum, Indigofera, Senecio and Tephrosia were well represented. The patches were burnt alternately during July of every second year. They were monitored at regular intervals for three years and a composite plant list was compiled for each patch.

A third patch was identified and evaluated, but since this area had previously been used to cultivate Black Wattle, it had low indigenous species diversity and no further monitoring was undertaken.

It was found that post-burn, the number of species increased gradually in richness and diversity, with the peak flowering period usually August-September but varying slightly with weather conditions. This applied to both patches. In the year when the patches were not burnt, the number of species observed decreased significantly, with isolated plants struggling through the long grass. Smaller, low growing plants, such as Turraea pulchella (VU), were particularly affected by the abundance of surrounding plant growth.  It was also noted that drought conditions during 2015 contributed to a reduction in post-burn species richness and diversity.

Although the grassland plants generally benefit from fire, some plants are less able to withstand fire and their existence is sustained by the protection of rocks and rock plates. One example is Aspalathus abbottii (VU), a woody shrub that grows on and between rock sheets. Seeds that fall on the bare ground do germinate but young seedlings are vulnerable to fire, while the plants among rocks and on rock sheets survive. In the absence of fire, A. abbottii shrubs can grow up to 2 m tall but they appear to succumb to senescence.

Since many of the special plants in the region occur on private properties, supporting continued conservation of these sites is very important. We found that compiling plant lists for these sites and providing farmers with information about species of conservation concern and the high incidence of endemism in the area, increases awareness of the need for conservation as well as enthusiasm about their plants. Given the outstanding biodiversity as well of the variety of habitats in the Oribi flats area, both on private properties and in reserves, this should be a conservation priority in years to come.

About the author. 

Kate is a citizen scientist with a passion for indigenous plants as well as botanical art.  As members of CREW, she and Graham have explored wide ranging areas of southwestern KwaZulu-Natal and the adjoining regions of the Eastern Cape. They recently compiled a book on the special plants of the Pondoland Centre of plant endemism, produced by SANBI (Strelitzia 47).