Serruria triternata (Thunb.) R.Br.
Common names: Tulbagh spiderhead, dill-leaf serruria (Eng.)
The Tulbagh spiderhead is a charming fynbos shrub suited to an informal indigenous garden. It is rather nondescript when not flowering but in spring time when it is in full bloom it is abuzz with a large variety of bees, butterflies and beetles.
Serruria triternata is an erect shrub growing 1 m tall and spreading to 0.5 m. In its natural habitat it is multi-stemmed, robust and sturdy. In cultivation it tends to have a more lax habit. Leaves are needle-like and curve upwards. They are 65-140 mm long and have hard tips.
Flowering occurs in spring with peak flowering in September. Attractive small silver white flowers are produced in dense flat-topped clusters along branch tips. Flower heads measure 120 mm across and consist of up to 25 headlets, each with 35 individual flowers.
Hairy brown seeds are produced two months after flowering.
The Tulbagh spiderhead is classified as Near Threatened (NT) which means it does not currently qualify for any of the threat categories but is listed in the Red Data book (Raimondo et al. 2009). Its distribution range is about 77 km² in natural mountain fynbos. This habitat is infested with alien pine and hakea which could pose a future threat.
Distribution and habitat
Serruria triternata grows in Hawequas Sandstone Fynbos (Mucina & Rutherford 2006) in the Elandskloof Mountains near Tulbagh. The average rainfall for this vegetation type is 1 197 mm per year, with most rain falling in the winter months of June, July and August. In winter the temperature does occasionally drop below freezing, with S. triternata being able to tolerate very light frosts. In summer hot, dry and often windy conditions are experienced with maximum temperatures reaching 35°C. On the mountains it grows on slopes at an altitude of between 400 and 950 m.
Derivation of name and historical aspects
The genus Serruria was named after Dr James Serrurier who was a professor of botany at Utrecht in the early 18th century. Triternata means three times divided into three, referring to the dissected leaves.
Serruria is one of 14 genera making up the Proteaceae family. There are about 55 species within Serruria, all of which are endemic to the winter rainfall fynbos region of the south-western Western Cape. Of these 55 species, 49 species are listed in the current Red Data List, a very scary thought!
The Tulbagh spiderhead is pollinated by various beetles, butterflies and moths. After pollination, seeds are produced and fall to the ground. Each seed has a white waxy tip at its base; this is called an elaiosome and is a favourite food of indigenous ants. Ants disperse the seed by carrying them underground to their nests where they eat off the elaiosome. The seed is now in safe storage, hidden away from predators like mice. Fire moves through the fynbos in late summer, killing all the mother plants of S. triternata. In early winter the rains begin and new seedlings germinate from the ant nests where they were safely protected from the fire.
The leaves of the Tulbagh spiderhead are tough and very narrow. This protects the plant from drying out in the hot sun and drying winds.
Serruria triternata was first collected for display at Kirstenbosch in 1988. It is not widely used in horticulture.
Growing Serruria triternata
Plant Serruria triternata in a sunny spot in well-drained soil. Planting on a slope will ensure good drainage. Plants become long and spindly in our gardens as they are pampered and receive too much moisture. As the foliage is rather unattractive, plant the Tulbagh spiderhead in amongst low shrubbery which will also help support the plant. At flowering the flowerheads can be enjoyed popping up amongst other plants.
Incorporate well-rotted compost into the soil before planting and feed twice a year during spring and autumn with a fertilizer specifically formulated for fynbos plants. Another option, instead of fertilising, is to mulch mature plantings with compost which breaks down and releases nutrients.
Water early while the morning is cool. This enables the plant to dry off before the heat of the midday sun. Watering during the heat of the day creates ideal growing conditions for fungi and bacteria. Apply a thick layer of mulch or plant matting groundcovers to keep the soil cool and moist for longer. Water new plantings often for the first couple of months, thereafter water can be reduced.
Spiderheads are not long-lived plants and require replacing every 4-5 years.
Propagate Serruria triternata from cuttings or seed.
Make cuttings from December to March (summer to autumn). Take cuttings 30-50 mm long from the current season's growth. Dip the cuttings into a rooting hormone solution or powder and plant into a medium of 50% polystyrene and 50% finely milled pine bark. Place in a growing house with bottom heat (25ºC) and intermittent mist. Once the roots are well developed, remove from the mist unit and harden off for three weeks. Plant the cuttings into small pots and grow on until ready to plant into the garden.
Sow seed in April when days are warm and nights start to cool down (late summer to autumn). Smoke-treat and dust the seed with a systemic fungicide. Sow the seed into a seed tray and place in a brightly lit position. Sow on a well-drained medium consisting of 1 part loam, 1 part bark, and 2 parts sand; firm down and cover with a layer of sifted sand. Germination begins after four weeks. Once two true leaves have appeared, prick the seedlings out into small pots or plugs. Place the seedlings in a lightly shaded area with good air circulation. When plants are ± 50-100 mm tall, or after one year's growth, they can be planted into the garden. Nipping out the tips of the seedlings will encourage branching and produce a neater shrub.
The best time to plant into the garden is at the start of the rainy season. This enables plants to establish themselves and send down deep roots before the hot, dry summer arrives.
- Mucina, L.& Rutherford, M.C. (eds) 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria. Sibis: SANBI's Integrated Biodiversity Information System. http://sibis.sanbi.org/
- Raimondo, D., Von Staden, L., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds) 2009. Red List of South African plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
- Rebelo, A. (Tony). 2001. Proteas: A field guide to the proteas of Southern Africa, edn 2. Fernwood Press & National Botanical Institute, Cape Town.
- Vogts, M. 1982. South Africa's Proteaceae, know them and grow them. Struik Publications, Cape Town.
Kirstenbosch National Botanical Garden
Plant Type: Shrub
SA Distribution: Western Cape
Soil type: Sandy, Loam
Flowering season: Spring, Winter
PH: Acid, Neutral
Flower colour: White, Cream
Aspect: Full Sun
Gardening skill: Challenging