Members of the Proteaceae offer the closest approximation of trees in fynbos. Some Leucadendrons, such as the famously beautiful Silver Tree, Leucadendron argenteum, attain 10 metres in height on the mid-slopes of Kirstenbosch. Restricted to granite outcrops on the Cape Peninsula, this lovely species was extensively felled for fuel well into the 19th century, and is now much reduced in abundance and occurrence. The protea family has 387 species in South Africa, of which 90 per cent occur in fynbos.
The geophytes are perhaps the most spectacularly beautiful of the Cape’s treasure trove of floral wonders. With some 2 200 species in the Cape, they have contributed greatly to the glamour and colour of gardens and homes in Europe – species, cultivars and hybrids of many members of gladiolus, watsonia, freesia, lachenalia, ornithogalum, ixia, amaryllis, etc, having been introduced abroad since the late 1700s.
Kirstenbosch National Botanical Garden Country Map Photo Gallery
Fire in fynbos is as ancient as the biome itself. Kirstenbosch has hadfrequent fires on the upper slopes of the Garden; here two helicopters in close formation help control the flames by dropping water from above.
Fingerprints of the past are to be found in what are known as palaeo-endemics. In the Cape, the endemic families Geissolomaceae, Grubbiaceae and Roridulaceae, and the nearendemic Bruniaceae and Lanariaceae, represent ancient groups from among the earliest flowering plants. Unlike the old flora of the Boreal Kingdom of Eurasia and North America, which was largely eliminated by the ice sheets and glaciers of the Pleistocene Ice Age – the African flora escaped the long glacial events of the Pleistocene. When the temperatures dropped by 5oC over the 100 000-year-long glacials, cold-sensitive species were able to retreat down mountainsides, and ascend again as the climate ameliorated during the warmer, but much shorter, 10 000-year interglacials. It was this warming and cooling during the Pleistocene, over a period of some 1.5 million years, that accelerated speciation in the Cape flora.
A narrow endemic, the famously beautiful Silver Tree Leucadendron argenteum grows naturally only on the Cape Peninsula.
Other characteristics of the region came into play: the diversity of landscapes, with mountain ranges rising to 2 000 metres close to the coast; a geological mix of coarse sandstones and soft shales; acidic and nutrient-poor soils, moderately fertile clays, and calcareous limestones; a variable climate, cool with high rainfall in midwinter, to arid, hot interior valleys in summer; and a mix of fire regimes. All provided the opportunity for rapid radiation of the flora on the interface between the older summer-rainfall areas of southern Africa and the emerging winter-rainfall zone that has developed over the past five million years. Within this area, many new endemics (or neo-endemics) within the families Mesembryanthemaceae, Ericaceae, Iridaceae, Proteaceae, Rutaceae, Rhamnaceae, Fabaceae, Polygalaceae and Rosaceae display the results of this rapid and recent speciation. Many of these species occur in sites of very limited area, often on mountain tops – with many peaks having their own individual endemics – or on the localised limestone outcrops of the Agulhas Plain.
Cowling explains the rapid speciation of short-lived fynbos shrubs by referring to the isolation of gene pools of populations subject to recurrent fire events, during which a whole generation of a species might be killed. Species that depend on ants to disperse and bury their seeds re-establish as isolated patches, thus avoiding both intergenerational gene flow (because no mature plants survive the fire) and the introduction of genes from distant populations, because of the limited area occupied by individual populations. Such ‘catastrophic’ evolutionary events, where populations go through a genetic bottleneck, are conducive to the formation of new gene complexes, leading to the evolution of new species. The steep environmental gradients found in the Fynbos Biome offer multiple opportunities for such isolation events.