Leucospermum harpagonatum Rourke
Common names: McGregor pincushion
An unusual creeping, mat-forming pincushion, with reddish, trailing stems and pinkish red flower heads in spring, that makes a pleasant groundcover for a sunny slope.
Leucospermum harpagonatum is an evergreen, creeping shrublet, with a single main stem, that spreads about 1–4 m wide and reaches a height of 0.2 m. The leaves are about 40–110 mm long and 2–10 mm in diameter, linear to narrowly oblong, folded inwards and slightly curved. Leaves are always pointed upwards. The leaf tip has a single tooth. New leaves are hairy, but are hairless when mature.
The flowering branches can produce approximately 25, axillary inflorescences. These branches are usually reddish, carrying the heads of cream-coloured flowers that will later turn to pink and carmine. A single flower head is made up of 7–12 flowers, with 25–35, well-developed involucral bracts. Each flower carries a pollen presenter covered by yellow pollen on styles that curve towards the inside of the flower head. The flowers appear in early spring to midsummer (August to November) and release seeds 1–2 months after flowering. The fruit is greyish white and drops to the ground when ripe.
Leucospermum harpagonatum can be confused with L. hamatum. However, L. hamatum has 3 or 4 involucral bracts or the involucral bracts can sometimes be absent completely, only 4–7 flowers per flower head and the leaves usually have 3 apical teeth. Although closely related, these species are distributed in different localities and habitats, about 200 km apart.
Because of its single small population and other factors, Leucospermum harpagonatum is assessed as Critically Endangered (CR) by the Red List of South African plants. The threats to this species include too frequent fires in the area occurring before the seedbank has had time to develop, the impact of alien invasive ants that feed on the elaiosomes and leave the seeds unburied, that results in seeds being either destroyed by fire or eaten by animals, and the harvesting of cut flowers that reduces the number of seeds produced by the plant.
Distribution and habitat
Leucospermum harpagonatum is endemic to the Riviersonderend Mountains at Olifantsdoorns near McGregor in the Western Cape. There is only one known locality of a single population of about 200 plants. This species grows in rocky outcrops on the northern slopes of the mountain, in sandy and rocky soil at a high altitude of 750–800 m.
Derivation of name and historical aspects
The generic name Leucospermum means ‘white seed’ and is derived from the Greek word leukas, meaning ‘white’ and spermum, meaning ‘seed’. The genus was named by Robert Brown in 1810. The white seed refers to a white layer that covers the seed, called an elaiosome or ant-fruit, which was discovered in 1984. The species name harpagonatum is derived from the Latin word harpago, which means ‘grappling iron’ and the suffix -atum, indicating a likeness to something, in this case the likeness of the flower head, with its inward bending styles, to a grappling hook.
The English common name for the genus, pincushion, refers to the mass of styles sticking out of the flower head that look like pins on a cushion. Leucospermum is one of the genera in the Proteaceae, a family that consists of 14 genera in southern Africa, most of which occur in fynbos. Leucospermum has 51 taxa of 48 species of which 2 species are outside South Africa and 3 species outside the Cape.
The first botanist to discover Leucospermum harpagonatum for science was Dr Tony Rebelo, in 1993. The South African botanist and Proteaceae specialist Dr John Patrick Rourke completed the description and writing up of the species a year after it was discovered.
The hook pincushions, L. harpagonatum and L. hamatum, are both pollinated by mice and rats. The plant produces a hard, nut-like, seed coat that is covered with an elaiosome, which ants feed on. During the fruiting season, the ants carry the seeds to their nest underground and remove and eat the elaiosome, but leave the seeds undamaged in their nest, where it will be protected from fire and other animals. These ants do not harm the seeds, but they help in the conservation of the seeds.
Rodents, korhaans, pigs and squirrels eat the seeds. Rodents also feed on the nectar that collects in the perianth tube and may pollinate the seed in this way. Rodents can also cause damage during nectar feeding by chewing both the style and perianth. Rodents and insects may eat the seedlings that emerge in a burnt environment free of competition. Alien invader argentine ants also feed on the elaiosome, but they don’t bury the seed and the exposed seed is then eaten by animals or burned by fire.
The hard seed coat restricts the penetration of oxygen to the seed embryo. This delays the germination of the seed. Buried seeds will germinate when the soil temperature is cool during the night and senescent plants are removed by fire.
Leucospermum harpagonatum is killed by fire, and the population regenerates by means of stored seeds.
Leucospermums have 3 or more glandular tips on the leaves, which are thought to function as nectaries for attracting wasps and ants. It is assumed that these insects in turn prey on other insects that feed on the young leaves (Rebelo 2000).
Leucospermum harpagonatum can be used as a groundcover in fynbos gardens, to fill up open spaces.
Growing Leucospermum harpagonatum
Leucospermum harpagonatum is propagated by both seed and cuttings. Collect the seed 1 or 2 months after flowering. Seeds are rarely found in cultivated plants, maybe because of a lack of natural pollinators. The ripened seed can be seen when the individual florets are turning brown. Cut the heads and dry them and store the seed in a cool room for 2 weeks prior to sowing. The seeds are hard and covered with elaiosome. Soak the seeds in a 1% solution of hydrogen peroxide for 24 hours to soften the seed coat and remove the elaiosome by rubbing on them in the bags or by using your fingers. Remove all the soft or squashed seeds as these are immature. Treat the seeds with a light dusting of a fungicide before sowing and apply fungicide once a week after planting to prevent fungal infections. The seed should not be allowed to dry out and must be sowed immediately after dusting it with the fungicide. Both seed and plants are susceptible to fungal infections. Sow the seed in autumn (March to May) using a well-aerated growing medium and smoke the seed with dry and green fynbos materials. Use a smoking tent or smoking bags to treat the seed. The seedlings are ready for potting-up when they have produced their first true leaves.
Take semi-hardwood cuttings in autumn and spring and treat them with a rooting hormone for at least 5 seconds to stimulate rooting. Because the leaves are curved in an upright position, it is easy to insert cuttings upside down. Take care to place the cuttings with the nodes pointing up. Plant cuttings in a well-drained and aerated medium of 70% perlite and 30% fine bark or coarse sand and finely milled pine bark. Insert the cuttings in multi-trays with sufficient space between each cutting to allow free air circulation. Place trays on heated benches of 25ºC with intermittent mist. Regularly treat the cuttings with a fungicide to prevent fungal infections. Remove the dead leaves and wilting cuttings while waiting for cuttings to root. Move the rooted cuttings to the hardening-off house for about 2 weeks and pot the cuttings into small nursery plastic bags, using a mixture of well-drained acidic planting medium.
The seedlings or cuttings are placed under a shade net in the nursery until they are ready to be planted in the garden after a period of 2 to 3 years. Net shade reduces the direct sun which can dry out the soil in the plastic bags and can scorch young plants. The pH level of the planting medium should preferably be acidic, between 5–7 pH.
Grow Leucospermum harpagonatum in a sunny position, in well-drained, sandy, acidic soil where there is free circulation of air. It is best suited to a north-facing slope, on terrace or gabion walls, and in rockeries. This creeping shrublet has potential for hanging baskets, as it cascades very well in a pot.
Keep the soil moist during the hot dry season, by applying a 5 mm thick mulch to the bed. The mulch will keep the roots cool, keep moisture in the soil and reduce the growth of weeds. Chipping mulch is commonly recommended, as it breaks down very slowly and also releases small amounts of nutrients to the plant. Prune creeping branches that are growing over the edges or to minimise the spread of branches.
Leucospermum harpagonatum is not prone to pest attacks. The plants are susceptible to root rot and grafted plants have a higher survival rate. L. harpagonatum can be grafted on the scion of the hybrid ‘Veld Fire’, a cross between Leucospermum glabrum and L. conocarpodendron subsp. conocarpodendron. Grafted plants live longer than rooted ones and can better resist fungal infections in the garden.
- Duncan, G., Brown, N. & Nurrish, L. 2013. Grow proteas. Kirstenbosch Gardening Series. South African National Biodiversity Institute, Cape Town.
- Rebelo, A.G. 2000. Proteas of the Cape Peninsula. Protea Atlas Project. National Botanical Institute, Cape Town.
- Rebelo, A.G. 2001. Proteas. A field guide to the proteas of southern Africa. Fernwood Press, Vlaeberg, Cape Town.
- Rebelo, A.G., et al. 2006. Leucospermum harpagonatum Rourke. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2020/02/25
- Rourke, J.P. 1994. Notes on African plants. Proteaceae. A new species of Leucospermum from the southwestern Cape. Bothalia 24, 2: 167–170.
- Wikipedia. Leucospermum harpagonatum. https://en.wikipedia.org/wiki/Leucospermum_harpagonatum. Accessed 24 February 2020.
Kirstenbosch National Botanical Garden
Plant Type: Ground Cover, Shrub
SA Distribution: Western Cape
Soil type: Sandy
Flowering season: Spring, Early Summer
Flower colour: Red, Pink, Cream
Aspect: Full Sun
Gardening skill: Average