Silver tree  (Leucadendron argenteum)

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1).

This beautiful tree grows on the slopes of Table Mountain, South Africa, and gets its name from its curious silver sheen, caused by abundant fine, satiny hairs covering the grey-green leaves, that glisten in the sunlight (2) (3). These tiny hairs also give the leaves a soft, velvety feel (2). The small silver tree has a stout trunk with thick grey bark, and grows symmetrically, with its upright branches bearing the long, tapering leaves, which overlap each other to conceal the thick branches (2).

Possibly endemic to the slopes of Table Mountain, South Africa, from Lion's Head to Noordhoek. Four small populations occur off the Cape Peninsula, but these may have been planted (1).

The silver tree grows on moist, usually south-facing slopes, on granite clays in fynbos vegetation and on the margins of forest patches (1).

The dioecious silver tree flowers in the spring months of September and October, bearing the male and female flowers on separate plants (2). After pollination, thought to be carried out by insects, female plants produce woody cones containing fruits and seeds (3), with the fruit ripening over several months and not being released from the cones for some years. When released, usually in the autumn months, the fruits do not immediately fall to the ground but remain loosely within the cone with each fruit's ‘parachute’ protruding. The parachute is the dried part of the old flower which, still attached to the seed, is a special adaptation for wind dispersal. The strong winds that occur on the slopes of Table Mountain eventually dislodge the fruit, and this natural parachute can be transported considerable distances (2). Large numbers of the fruits are eaten by rodents, but a sufficient number survive to allow new plants to germinate; the fruit are known to survive in the soil for 80 years (4).

Silver trees live for 15 to 80 years, depending on the intervals between the fires that occur naturally in fynbos habitat. A few taller plants survive cooler fires, but recruitment of seedlings only occurs the year following a fire (4). Silver trees are also susceptible to Phytophthora root rot, but only about five percent of the populations die each year and thus the disease is not considered a threat to the species (4).

The thousand of tiny hairs that cover the surface of each leaf give the tree its attractive silver sheen and also play an important role in protecting the plant from desiccation and herbivory (4). The intensity of the silver sheen varies with temperature; in wet weather the hairs stand erect, allowing free circulation of air around the leaves and the leaves appear fairly drab. In hot, dry weather the hairs lie flat on the leaves, and the sheen is pronounced (4).

In the past, the leaves of the silver tree were pressed, dried and used by artists for painting scenes for sale as souvenirs. It has even been suggested that the collection of leaves may have been a major factor in the extermination of the silver tree on the north slopes of Table Mountain (4). Today, the expansion of Cape Town and the establishment of tree plantations continue to cause reductions in population numbers (1). An increase in the frequency of fires may also pose a threat to silver tree populations. Even within protected areas, populations of silver trees suffer from invasions by alien plant species (1).

Almost half of the entire population of the silver tree occurs within protected areas, and programmes to eradicate alien plants species are in place (1). In addition, the Parks and Forestry department of South Africa plants around 1,000 silver trees each year on the Cape Peninsula. However, few of these are planted under ideal conditions and most die within a few years (4). The silver tree is also cultivated commercially for its decorative foliage (3).

For further information on the silver tree see:

• Protea Atlas Project:
  protea.worldonline.co.za/silver.htm