Leucadendron pubescens R. Br.
Common names: grey conebush, silky conebush (Eng.); knokkerbos, pitjiebos, knopbos, syhaartolbos, pitjieknopbos, syhaar-tolbos (Afr.)
SA Tree No: 81.3
A very attractive shrub with twisted, hairy leaves and large maroon-brown cones that are very noticeable in winter and spring when the plants are flowering and fruiting.
Leucadendron pubescens is an upright, dense, evergreen shrub, that grows 0.6–2.5 m tall, from a single stem. The leaves are greyish-green, oblanceolate, narrow at the base, covered with silvery hairs, becoming less hairy when older. Both stems and leaves are hairy, the stem becoming hairless when older. The leaves are twisted and differ in size between male and female plants: on female plants they are about 25–57 mm long and 7–15 mm wide and on male plants they are 16–28 mm long and 3–7 mm wide.
The female flowerheads are 10–20 mm while the male flowerheads are 6–10 mm in diameter. The flowers are greenish-yellow or cream coloured, and the female flowerheads develop into large, globose, maroon-brown or grey cone-like fruits, 32–40 mm in diameter, covered with silvery-grey hairs. Involucral bracts and perianth are both hairy, pointed at the tip, with style shorter than 10 mm.
Leucadendron pubescens begins to flower in winter and continues into spring (July to October) and peaks in July. The seeds are nut-like, 11 mm in diameter, and ripen in October but can start as early as September and finish as late as January.
Leucadendron pubescens has many variations and 6 of them were previously considered to be different species. The northern forms have smaller leaves; the Citrusdal form with a conspicuous crowded involucre; the Cederberg form has dwarf plants with silvery leaves; on Touwsberg they have very pointed leaves; at Karoopoort male plants have very large leaves; and in Koue Bokkeveld and Ezelbank the populations have silver leaves, and there are hairless plants in many populations.
Leucadendron pubescens is assessed as Least Concern (LC) on the Red List of South African plants. Although the population has been declining, the species is widespread and abundant and is not in danger of extinction. The decline is mainly due to the expansion of cultivation of rooibos tea and potatoes in the deep sandy soils the deep sandy soils of the Bokkeveld Escarpment and Sandveld, with some habitat also lost to fruit orchards in the Koue Bokkeveld. The other minor threats are frequent fires, which leave the species vulnerable as it regenerates by seed after fire, and the overstocking of livestock in the natural habitat, which degrades the land. It is recorded that 23% of the habitat has already been lost and the loss continues but at a relatively slow rate in the montane areas and 3% is expected to be lost in the next 24 years.
Distribution and habitat
Leucadendron pubescens occurs in two provinces, Northern Cape and Western Cape, where it grows on the Bokkeveld escarpment, in Oorlogskloof, Gifberg, Cederberg, Piketberg, Olifants River, Sandveld, Koue Bokkeveld, Hex River, Bonteberg and Kwadouw Mountains, and on the Witteberg and Touwsberg. More than 100 subpopulations are found growing at 60–1 700 m altitude, on flats and slopes in sandstone and quartzite soils, in dense stands.
Derivation of name and historical aspects
The name Leucadendron is derived from the Greek words leukos, which means ‘white’ and dendron, which means ‘tree’, because this genus was named after Leucadendron argenteum, commonly known as silver tree, but which the early Dutch settlers called witteboom meaning ‘white tree’. A botanist named Plukenet used the genus name Leucadendron to describe the silver tree and related plants in the 1690s. The species name pubescens refers to the silky, silvery or soft, downy hairs on the leaves and cones.
Leucadendron is one of 14 genera of the Proteaceae. It comprises of 83 species within the genus. Proteaceae is one of the most prominent flowering plant families. There are about 1 400 species, in more than 60 genera in the southern hemisphere. Australia has 45 genera, followed by Africa with 14 genera, of which more than 330 species occur in the Cape Floristic Region alone. Other countries where they occur include Central and South America, islands east of New Guinea, New Caledonia, Madagascar, southeast Asia, New Guinea and New Zealand.
Leucadendron pubescens has female and male flowers on separate plants (dioecious). This species is pollinated by insects, which are attracted by the yeast scented flowers. When the nut-like seeds are ripe, they immediately drop to the ground and are dispersed by small mammals, that collect them and bury them in caches. Although they consume some of the seeds, many are left uneaten and are stored underground, safe from other seed-eaters and fire. Exposed seeds are left to be eaten by rodents, korhaans, pigs, squirrels and doves, or are burned by fire.
Leucadendron pubescens is killed by fire and reproduces by banked seeds in the ground (reseeder). The stored or underground seeds will germinate when senescent plants are removed by fire, and the soil temperature is cool during the night and warm during the day; this is typical of autumn conditions, just prior to the onset of the winter rains. Rodents and insects may eat the seedlings that emerge in a burnt environment free of competition from other plants.
Leucadendron pubescens makes a wonderful attractive plant for big or small fynbos gardens. The spectacular silver cones and hairy leaves create an outstanding display when planted with companion plants such as Metalasia spp, Leucadendron argenteum, Passerina and restios. This plant has been used in the cut flower industry.
The nut-like seeds are delicious and are a wild edible fruit harvested by the people of Clanwilliam. The seeds were ground to make a flour in the past. This species can be confused with Leucadendron galpinii from the south coast as it has similar grey leaves and cones, and it has been mistakenly traded under the name of Leucadendron pubescens.
Growing Leucadendron pubescens
Leucadendron pubescens is propagated by seeds and cuttings, and is best by seeds. The seeds are collected when they are about to drop, or when the cone-like fruit is about to open, in the months of September to January. The harvested fruits release the seeds when they are dry. The seeds can be stored in a cool dry room, optimum storage conditions are 15% humidity and 15°C temperature. Sow the seed in autumn (April to June) when the temperature has dropped, with longer cold nights and shorter warm days (5–10°C night and 15–20°C day). Treat the seeds with fungicide and smoke derived from burning wet and dry fynbos plant material to break the seed dormancy. Sow the seeds on well-drained fynbos mix, cover the seeds at about the same depth of the size of the seeds.
Germination takes place in 6 weeks after planting. Once the seedlings produce the first pair of true leaves, transplant them into plugs or 1 litre bags. Regularly treat the seedlings and cuttings with a fungicide to prevent fungal infections.
Take semi-hardwood cuttings in autumn and spring and treat with a rooting hormone to stimulate rooting. Cuttings should be taken in the morning to prevent loss of moisture, and dipped in a diluted fungicide for 5 seconds. Dip the cuttings in the rooting hormone for at least 5 seconds. Place your cuttings in a well-drained and aerated sowing medium of 70% perlite and 30% fine-milled bark or coarse sand and finely milled pine bark. Insert the cuttings in the multitrays with sufficient space between each cutting, to allow air circulation and place them on the heated benches of 25ºC, under intermittent mist.
Hairy, silvery proteas are infected easily and need effective monitoring. Remove the dead leaves and wilting cuttings until your cuttings are rooted. Move the rooted cuttings to the hardening-off house for about 2 weeks and transfer the cuttings into small, nursery bags or pots, using a fynbos soil mixture that is well drained and acidic preferably between 5–7 pH levels.
The seedlings or cuttings are placed under shade netting in the nursery until they are ready to be planted into the garden, after a period of 2 to 3 years. Plants do not like to their roots to disturbed and need a good air circulation. Mulch the flowerbed with organic mulch to supress the weeds and keep the soil moist during the dry seasons.
Leucadendron pubescens is susceptible to Phytophthora cinnamomi root rot disease. This can be eliminated by a good nursery hygiene and immediate removal and burning of the infected plants.
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- Vogts, M. 1982. South Africa's Proteaceae: know them and grow them. Struik, Cape Town.
Mane Somtshu and Mashudu Nndanduleni
Kirstenbosch National Botanical Garden
Plant Type: Shrub
SA Distribution: Northern Cape, Western Cape
Soil type: Sandy, Loam
Flowering season: Spring, Winter
Flower colour: Cream
Gardening skill: Average