Leucadendron argenteum Family: Proteaceae (Protea Family) Common Names: Silver Tree (Eng.) Silwerboom, Witteboom (Afr.)
Unique to Table Mountain
The famous silver tree is as much a feature of Cape Town as the flat-topped Mountain. These giant silver proteas with their silky, shimmering leaves grow wild on the slopes above Kirstenbosch. You can see them from the Garden - look for the silver-grey patches on the lower slopes.
Historical records suggest that Silver trees occurred all over the lower northern slopes of Table Mountain centred on the watermill at Platteklip. It was sufficiently common and noticeable to inspire land owners to name their farms Witteboom and Silverhurst (hurst = wooded hill).
The genus is named after its most outstanding member, Leucadendron argenteum …. known to botanists, gardeners and plant lovers throughout the world as the Silver tree, but the early Dutch settlers dubbed it witteboom, literally ‘white tree’. In 1691 the botanist Plukenet used the name, translated into Latin, to describe the witteboom and related plants …. Leucadendron therefore, became the accepted name for this genus.
The Silver tree (Leucadendron argenteum) is one of eighty species of this dioecious genus. It belongs to a family (Proteaceae) of great antiquity, fossils dating back to the time when the great southern continent Gondwanaland started splitting apart. Nowadays, the family (Proteaceae) is represented on all its daughter continents except Antarctica. In the winter-rainfall flora of the Cape Province, there are many genera and species of this ancient family, but Leucadendron probably reflects a relatively recent evolutionary direction for the family; only one other proteaceous genus in this region is dioecious.
The characteristic silver sheen of the leaves is due to thousands of hairs which cover the leaf and protect the plant from desiccation and herbivory. The intensity of the sheen varies with temperature and is most pronounced in hot, dry weather when the hairs lie flat on the leaves. During wet weather the hairs stand more erect allowing free circulation of air around the leaves and the leaves are relatively drab.
In nature they are found only on the cool, east- and south-facing slopes of the Table Mountain chain. In the 1700s and 1800s Silver Trees were widely planted for firewood, and it is thought that the Silver Trees that grow in Paarl, Somerset West and Stellenbosch are not natural but were planted in those days and have naturalised.
Nowadays, the uses to which we put silver tree are mostly ornamental, but an architect who has restored many of the grand, old, thatched, Cape Dutch houses reports that those on the Cape Peninsula used silver tree beams and perlons in their roofs; the wood is particularly strong due to its distinctive cross-banded structure. In the time of the Dutch East India Company (prior to the 1800s), the nuts were harvested as a supplementary feed for pigs taken by the sailing fleet on its long return trip from Batavia to Holland. The leaves have been sold as bookmarks, as a base for the painting of little Cape scenes as souvenirs, or for incorporating into wreaths. The leaf trade became so excessive that, by the mid-twentieth century, a ban had been placed on their harvest, bringing to an end a pretty source of pocket money for local children. All these uses point to how common silver tree was in the early days of settlement at the Cape.
Rare and Endangered
The Silver Tree is classified as Rare, because it has a small wild population and a small distribution range. Its Red List status is Endangered and it is estimated that this species could go extinct in the wild in the next 50 years if the remaining wild populations are not properly cared for.
The superabundance of silver trees is a thing of the past for, in the 1930s, a disease suddenly appeared, and trees of all ages and health started yellowing, wilting, and dying. A botanist employed at Kirstenbosch discovered that a borer beetle seemed to be associated with the disease. By the 1940s, the problem had become so acute that a plant pathologist was called in to investigate the dying trees. He established the identity of the beetle, an indigenous buprestid that bored into the trunk, mostly near ground level. He concluded that the beetle was probably not the first cause, but perhaps only an agent of some recent pathogen not previously present at the Cape. In 1975 the fungus Phytophthora cinnamomi, imported by accident some time before from the Far East to South Africa was implicated. The only practical advice to come out of these investigations was a suggestion to maintain a thick growth of shrubs underneath silver trees to hamper the beetle’s access to the base of the trunks—a council of despair, for there is still for there is still no satisfactory answer to the die-off, and silver trees are still prone to it; for this reason, they have now become scarce and vulnerable.
Quite easy to grow under the right conditions
The Silver Tree has a reputation for being very difficult to grow, mainly because it is very susceptible to the phytophtora root rot fungus. Is also dislikes wet, soggy, rich soils and humid air. But if you have a cool but sunny, well-drained slope where their roots will be as undisturbed as possible they grow fast and well, and can thrive far away from home.
A fast-growing ornamental tree 7-10 m tall, with large light reflecting silver grey leaves, spring flowering (September), wind tolerant, foliage useful for flower arrangements.
Boy or Girl?
Did you know that Silver Trees are either male or female? Male and female flowers are borne on spear plants. The term for this is dioecious (die-ee-shuss).
Male and female trees are quite easy to tell apart. On a female tree, you will see woody cones(90mmx60mm) on the older stems - silver while they are young. The male tree has none.
Looking at the flowerhead, which you will see in spring (September - October) you will notice the male flowerhead is made up of many yellow and silver flowers packed into a round bay.
The female flower head is a silver ball with a few hairy creamy/yellowish flowers dotted on it. The flowerhead have a faint sweet scent which attracts the small beetles that do the job of pollination.
Our custom designed Itineraries are always arranged and planned around the unique preference and interests of our clients.
We would love to have you join us on a bespoke private tour that could include a visit to Kirstenbosch National Botanical Garden to see the Silver trees.
Let us know when you would like to visit!
Tours and itineraries are available as private, fully guided with driver/guide and transport included or self-drive.
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Sources:
PlantZAfrica.com
Marie Vogts, South Africa’s Proteaceae, Pacific Horticulture
Protea Atlas Project