The Succulent Karoo Biome

The Cape Floristic Region at the south-westernmost tip of Africa is the smallest of the world’s six recognised floral kingdoms. The Fynbos Biome is found along the Cape Fold Mountain belt and its Atlantic coast dunefields. The Succulent Karoo Biome occupies the arid part of coastal southern Namibia into South Africa eastwards around the edge of the Great Escarpment. The Great Karoo is a different biome, with Nama-Karoo grassland and shrubland.

Besides their high biodiversity, the Fynbos and Succulent Karoo are united by their abundance of geophyte species (underground bulbs) and lack of trees. The key difference is that Fynbos plants have hard leaves (sclerophyllous) and, as its name suggests, Succulent Karoo plants tend to have fleshy, succulent leaves. Typical fynbos plants include restios (grass-like reeds), ericas (heath plants) and proteas (woody flowering shrubs).

Broadly the Fynbos Biome coincides with Cape Supergroup geology and the Succulent Karoo with the shaley lower levels of the Karoo Supergroup. These geologies produce different soil types, containing varying nutrients and moisture levels, which each plant community is specifically adapted to.

The Succulent Karoo Biome is the world’s only arid biodiversity ‘hotspot’. These hotspots make up only 1.4% of the world’s land but contain 60% of all terrestrial species diversity. The Succulent Karoo is especially famous for its diversity in succulent plants, containing about a third of the world’s species, 40% of which are endemic, meaning that they are only found in this region. In particular, plants in the Mesembryanthemaceae and Crassulaceae families are important.

Mesembryanthemum sp.
Source: Emily Hallinan
Crassula sp.
Source: Emily Hallinan

Desert-adapted or xerophytic plants have adapted to the harsh conditions of environments like the Karoo in a number of ways. Succulents store water in their fleshy leaves, with a waxy coating to reduce transpiration. Tiny stone plants not only disguise themselves as pebbles, but they have also developed a special translucent window in their flat upper leaf to get enough sunlight to photosynthesize but it also screens out harmful UV rays. Geophytes store their nutrients in an underground bulb, making them an important carbohydrate source for hunter-gatherers. Some plants have adapted by growing their leaves in a spiral shape to protect them from the wind and retain moisture. Others have developed spines to protect them from grazing animals seeking a source of moisture and nutrition.

Dipcadi crispum
Source: Emily Hallinan
Albuca uniflora
Source: Kevin Murray
Lithops or stone plant
Source: pxfuel
Sarcocaulon crassicaule
Source: Emily Hallinan

Despite its low annual rainfall (less than 100 mm), this winter rainfall is reliable and droughts are rare, setting this region apart from the other deserts in the world. After winter rains in the spring, the fertile alluvial plains burst into flower with daisies (Asteraceae), attracting grazing animals (and tourists). Its diverse wildlife would have provided appealing foraging opportunities for past hunter-gatherers, even if only at certain times of the year.

Following winter rains, the fertile Tankwa plains come alive with the colours of spring wildflowers
Source: Emily Hallinan

The Tankwa Karoo National Park is a protected area comprising lowland Tanqua Karoo and upland Western Mountain Karoo vegetation types. Below is a gallery of some of the desert-adapted flora we have encountered during surveys there.

Albuca spiralis
Gethyllis villosa
Haemanthus crispus
Amellus tridactylus
Boophane haemanthoides
Lampranthus uniflorus
Gazania lichtensteinii
Lapeirousia plicata
Psora crenata
Desert pavement with succulents
Euphorbia and Hoodia
Hammeria meleagris
Bulbine succulenta
Morea and Lachenalia
Mesembryanthemum guerichianum
Mesembryanthemum guerichianum
Aptosimum procumbens
Psilocaulon junceum
Trachyandra flexifolia
Euryops annus
Hoodia gordonii

Source: Emily Hallinan and Matthew Shaw
Please contact me if you notice any plant misidentifications; we are archaeologists not botanists!

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