Roots of desert succulent a succour for rodents and strange subterranean plants

One year ago, South Africa was at the bitter tail end of a three-year drought. A drought that led to a demand for residents of Cape Town to reduce water usage from 200 litres per person per day to only 50. The respected scientific journal Nature described that target as the amount of water in a water tub filled to 10 cm. Not much.

The drought exposed the social divide in the city where poorer people had always existed on that kind of water ration, or less. For the better off, this now meant letting gardens die and using shower water to flush toilets. All this to avoid a 'day zero', when Cape Town would run out of water.

In May, the rains came. Saving the city on this occasion. Decisions made in preceding decades were, according to Nature, 'short-sighted'. The problem was caused it seems mostly by poor managed of limited water resources, compounded perhaps by climate change. The latter will only add to the problem in coming years.

When I visited in August the threat was over but the warnings remained - literally, in airports, public toilets and in hotels. Sensibly, the focus on maintaining an adequate water supply remains. Better decisions will also need to be made to cope with increases in population and general living standards. 

For me as a botanist I was keen to note any plants that might survive in gardens under these kind of restrictions. Here in Australia we might choose succulents and some of our more robust Australian plants such as the correas and wattles that seem, once established, to survive hot and dry summers in our home garden.

One elegant plant native to South Africa, I think, is this euphorb, Euphorbia dregeana. It's known locally as the Namaqua Milkbush. The milk is the typical sap inside many euphorbs and has been used to make rubber.

While it can theoretically survive harsh summers it has one problem, rodents. As explained in the sign on this specimen in Karoo Desert National Botanical Garden, during 'extreme' drought the local wildlife will dig up roots to extract water. 

The roots are in great demand. There is a bizarre root parasite, called Hydnora triceps, that flowers underground (like in Australia, the unrelated Thismia and Rhizanthella). This is the flower...

The genus Hydnora has, with good reason, been promoted as 'the strangest plant in the world'. Hydnora triceps is rare, but then so is the Namaqua Milkbush in South Africa, where it grows in rocky shrubland like this in Little and Great Namaqualand. 

I gather the Namaqua Milkweed it is more common further north, in Namibia, and you will find it in horticulture inside and outside Africa. I didn't see its root parasite, or any rodents, on my visit to Karoo Desert National Botanical Garden. However I did see plenty of rain.

Images: Except for one, from my trip to South Africa in August 2018. The image of Hydnora triceps is by Lytton Musselman, from the Parasitic Plant Connection, hosted by Southern Illinois University Carbondale.


nguyenlien said…
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