CONSERVATION

Bloodcobs & Vampire Cups: The Secret Life of Parasitic Plants

OCT 26, 2020 | Written by Zoë Chapman Poulsen. Photos by Ann Symonds, David Rosenthal, Seth Musker, Tony Rebelo, Klaus Werhlin, ‘jimbohutthehun’ and Douglas Euston-Brown. www.inaturalist.org

Above: Cytinus sanguineus. Photo: Ann Symonds. www.inaturalist.org.

This week on 31 October the festival of Halloween comes around, turning our attention to all things gruesome, ghostly and spooky. In honour of this we thought it no better time to have some fun learning about the creepy, bizarre and fascinating world of parasitic plants.

What are parasitic plants?

A parasitic plant is defined as a plant that derives all of its nutrients from another plant through various different adaptations. This is actually a more common phenomena than one might think, comprising around 1% of angiosperms (flowering plants). In line with the megadiversity of South Africa’s flora, there are also an extraordinary diversity of parasitic plants. This week on the BotSoc Blog we will be taking a closer look.

Above: Hyobanche sanguinea. Photo: David Rosenthal. www.inaturalist.org.

How are parasitic plants classified?

There are various different adaptations that parasitic plants have that allow them to exploit their hosts. Stem parasites and root parasites attach themselves to the stems and roots of their host plants respectively. A hemiparasite is a parasitic plant that photosynthesises to some degree, deriving predominantly water and mineral nutrients from the host plant. A holoparasite derives all of its fixed carbon from the host plant and cannot photosynthesise itself.

Cute, fluffy & pink: The genus Hyobanche

Those exploring various vegetation types on nutrient poor soils are likely to encounter one of these striking and bizarre looking plants. There are eight members of the genus but the most common is Hyobanche sanguinea, distributed across the country northwards to the Gariep River and eastwards to Lesotho and eSwatini.

Also known as ‘Cat’s Claws’, it is a holoparasite, thus meaning it does not photosynthesise. Instead it attaches itself to various different host plants using a long fleshy organ known as a haustorium. This can grow up to two metres in length on its hunt to find an appropriate host plant. One plant can be attached to multiple hosts of different species at the same time.

Above: Hydnora africana. Photo: Seth Musker. www.inaturalist.org.

Putrid smells & rotting flesh: Hydnora africana

Also known as Jackal Food, Hydnora africana is a strong competitor for the title of most bizarre-looking plant on the African continent. In fact, it looks more like a fungus than a member of the plant kingdom. Hydnora africana parasitises on members of the genus Euphorbia and grows predominantly in semi-arid areas. Historically this species also once grew in sand fynbos north and east of Cape Town.

Following good rains flower buds emerge from the soil, taking one year or more to develop. Upon opening they emit a putrid stench of rotting flesh to attract the carrion beetles that pollinate this species. One they arrive then they fall down within the flowers, becoming trapped by bristles that channel the insects further down to ensure successful pollination.

Above: Viscum capense. Photo: Tony Rebelo. www.inaturalist.org.

Romantic or not? Meet the Mistletoes

Mistletoes are a group of plants that are associated with superstition and romance, but in fact, their biology as parasitic plants is anything but romantic. They comprise members of the plant families Viscaceae and Loranthaceae, with many different species being distributed across South Africa.

Few species are found within nutrient poor fynbos, with the highest species diversity found in mesic savannas. Mistletoes grow on host trees and shrubs within the canopy attached to the branches. They are hemiparasites, thus meaning they do in fact photosynthesise.

Above: Harveya purpurea. Photo: Klaus Wehrlin. www.inaturalist.org.

A plant with no leaves: The genus Harveya

The genus Harveya is an African genus of parasitic plants comprising around 40 different species. Around 13 of these are found in southern Africa with other species found in Yemen, the Comores and Madagascar. Only their spectacular blooms are visible above the ground, as they do not photosynthesise. Host plants include species of Aspalathus, Cliffortia and Wildenowia.

Above: Cytinus visseri. Photo: ‘jimbohutthehun’. www.inaturalist.org.

The Vampire Cups: The genus Cytinus

Also known as ground roses, there are several different species of Cytinus found across South Africa. Mainly parasitising shrubby members of the Asteraceae or Daisy family, male and female flowers are found on different plants. Cytinus sanguineus is widely distributed on sandy soils from Namaqualand to Mossel Bay. The flowers are pollinated by sunbirds that transfer pollen on their beaks while drinking nectar from the flowers.

Above: Mystropetalon thomii. Photo: Douglas Euston-Brown. www.inaturalist.org.

The Bloodcobs: The genus Mystropetalon

It is not hard after encountering either of the two species in this genera in South Africa to understand the derivation of its common name. Members of the genus Mystropetalon are rarely encountered despite their wide distribution, being found from the Hex River Mountains southwards to the Cape Peninsula and eastwards to Riversdale. Their host plants are members of the genera Protea and Leucadendron within the Proteaceae family. After they have flowered seed is set, which is then distributed by ants.

Further Reading

Dean, W.R.J. Midgley, J.J. Stock, W.J. (1994) ‘The distribution of Mistletoes in South Africa: Patterns of species richness and host choice’, Journal of Biogeography (Volume 21): pp. 503-510.

Visser, J. (1981) South African Parasitic Flowering Plants, Juta and Co, Cape Town, South Africa.