Floridata Article

Desert Life

Euphorbia namibensis
Photo 1. Euphorbia namibensis, the darkish lump between the figure and the lower edge of the photograph.
Euphorbia namibensis
Photo 2. A close-up of Euphorbia namibensis. It is about the size of a cantaloupe.
Euphorbia namibensis
Photo 3. Four plants of Euphorbia namibensis growing together. The brush-like plants are stubble remaining after a grass fire.

The single most critical and limiting factor for plant life is the availability of water. No where is this more evident than in a desert environment. Strategies to survive in such extreme conditions include deep root systems to reach what little water may exist, waxy leaves and reduced surface area to minimize evaporation, often a perennial life style, or, as is common in the flora of southern Africa, a dependence on geophytism, surviving the dry season as a dormant bulb. The first part of our visit to southern Africa took us into deserts, the Kalahari and Namib, where all of these strategies, and more, are necessary for survival. This is not to say that these areas do not get any precipitation - they certainly do - but that the amount they get is often only a passing shower, or a significant downpour leading to flash flooding. An extreme case involves the coast of Namibia where rainfall, almost unknown, is replaced by dense oceanic fog caused by the Benguela current flowing northward along the Atlantic coast. Thus, for a distance of 50 km or so inland from the coast, both plant and animal life depends upon collecting moisture through condensation of fog. This phenomenon can often be seen by the presence of damp sand on the windward side of desert shrubs. This was particularly evident with some succulents - probably some Crassulaceae - where the sand was damp to the touch. As well, beetles of some description were busily eating the flesh of the plants. Several drops of water could be squeezed readily from even very small leaf segments.

One of the most impressive desert survival specialists that we saw could easily have been overlooked had it not been pointed out to us by one of our local guides. He stopped our vehicle and led us a short distance into the otherwise nearly featureless bed of the Koichab River. If you examine Photo 1 you will see a darkish, lumpy object about half way between the figure and the front edge of the picture. Photo 2 is a close-up of the cantaloupe-sized, rock-hard Euphorbia namibensis (Euphorbiaceae), a species endemic to this part of the Namib Desert (also referred to, by the way, as the Namibian Sand Sea). Photo 3 shows four plants growing together. We were assured that they do flower, but that they require just the right amount of rain at just the right time—talk about fussy.

Euphorbia gummifera
Photo 4. Euphorbia gummifera, Namib Desert.
Euphorbia mauritanica habitat
Photo 5. Euphorbia mauritanica habitat near Klein Aus, Namibia.
Euphorbia mauritanica habitat
Photo 6. Euphorbia mauritanica, close-up of flowers.

A little farther along the track (road would be an exaggeration!), we left the riverbed and passed through an area that featured scattered plants of Euphorbia gummifera (Photo 4). This species, and the other 260 or so within the genus, are the Old World’s equivalent of the New World’s cactus family. There are no naturally occurring cacti in Africa, although a few species have been introduced as decorative plants. It was interesting then to see, later in our trip, that the Kirstenbosch Botanical Garden (Cape Town) features a display of Cactaceae that are invasive weeds in southern Africa.

Back at our lodge, the Wild Horse Inn in Klein Aus Vista, we spent our free time walking into the local rocky foothills that mark the boundary between the desert dunes and the Aus Mountains. One of the plants that we met, staying with the euphorbs for the moment, was Euphorbia mauritanica (Photo 5). A close-up of its flowers is shown in Photo 6. The Afrikaans name for this plant is “gifmelkbos” in reference to the milky latex that exudes whenever a plant part is broken. 

Sarcocaulon sp
Photo 7. Sarcocaulon sp. This member of the Geraniaceae is one tough customer.
Sarcocaulon sp
Photo 8. A closer shot of the Sarcocaulon sp.  Those are serious spines. 
desert rose bush
Photo 9. Hermannia stricta, the desert rose, growing in the rocks above Klein Aus, Namibia
desert rose bush
Photo 10. Hermannia stricta close-up. A rose by any other name...

Many euphorbs are highly toxic when ingested and/or produce nasty rashes when the latex comes in contact with the skin. There was no evidence of any nibbling on this specimen, but on at least one other unidentified Euphorbia—at a different site—leaf tips had been chewed upon. A local guide at that stop informed us that some antelope species eat small portions of these as ‘medicine’ for infestations of intestinal parasites.

The walk among the rocks at Klein Aus Vista revealed several other interesting plants, among which was a species of Sarcocaulon (Photo 7), a genus in the Geraniaceae with about a dozen species, all of which occur only in southern Africa. A common name for these plants is “bushman’s candles” in reference to the waxy stems which were used by the bushmen to light fires. Photo 8 shows a close-up of this specimen. Needless to say, some caution must be exercised in collecting specimens; I can only imagine the pleasure in trying to press an herbarium specimen.

Growing in the same habitat among the rocks was the shrub Hermannia stricta (Photos 9 and 10).  Hermannia, a member of the Sterculiaceae, consists of about 150 species in southern Africa, about three dozen of which occur in Namaqualand.

This species, known as the desert rose, or “woestynroos” in Afrikaans, is palatable to stock, and possesses a very fragrant flower. We also saw several yellow to yellow-orange-flowered species of Hermannia scattered throughout other dry areas.

Pelargonium spinosum.
Photo 11. Pelargonium spinosum.
Gladiolus saccatus
Photo 12. Gladiolus saccatus in a bed of ever-present yellow daisies.
Mexican poppy
Photo 13. An alien in Namibia, the native Mexican poppy Argemone ochroleuca.
Photo 14. Codon royenii, a member of the Hydrophyllaceae. Notice the deep floral tube in contrast to that of C. schenkii.
Codon schenkii
Photo 15. Codon schenkii. Notice the more open floral tube. 
Run-down buildings
Photo 16. Run-down buildings at Kolmanskop. Handy man’s special?
abandoned diamond mining community
Photo 17. Derelict homes at Kolmanskop, an abandoned diamond mining community..
Didelta carnosa var. tomentosa
Photo 18. Didelta carnosa var. tomentosa, a hardy member of the desert flora.
Sarcocaulon patersonii
Photo 19. Sarcocaulon patersonii growing in the abandoned mine area.

Growing next to the desert rose was a bush with diminutive flowers which, on closer inspection, proved to be a species of Pelargonium, P. spinosum (Photo 11), one of many representatives of this genus in southern Africa. While getting the close-up image of the pelargonium, a small flash of red caught my eye. Growing out of a clump of  ever-present yellow daisies nearby was Gladiolus saccatus (Anomalesia saccata in earlier treatments) (Photo 12). This was our first encounter with a ‘glad’ on the trip, of which there are over 160 species in southern Africa; we will see others in subsequent articles.

On our way back down the trail I noticed a flowering shrub that seemed familiar, an unusual occurrence in light of the overwhelming newness of almost everything we were seeing. Indeed, this almost old friend, pictured in Photo 13, turned out to be Argemone ochroleuca, a member of the Papaveraceae (poppy family) native to Mexico.

One of our (Lesley and my) botanical disputes on the trip was what to do with a plant that we had run into (painfully) in different places in the deserts. Photo 14 illustrates the first sighting of the genus Codon in our collective experience. Reference to our books suggested that it was C. royenii, a member of the Hydrophyllaceae. In Afrikaans it is called “soetdoringbos” or “suikerkelk,” with reference to the sweet nectar of the flowers. The difference of opinion arose when we found plants whose flowers had the appearance of those in Photo 15. Lesley immediately suggested that this was a different species and not C. royenii at all.

My idea was that it was simply a plant whose flowers had opened wider. It was back to the books, which informed us that Lesley was correct - as usual - and that we had found another species of the genus, C. schenkii. It turns out that there are only two species of this genus, and that we had been in perfect places to find them both.

One of the scheduled stops on our tour of Namibia was a visit to Kolmanskop, a deserted diamond mining town now converted to a museum. The town was established in 1908 to provide shelter and amenities for the diamond miners. These areas were not mined in the usual sense of the word—deep pits and the like—but were ‘cleaned’ of their diamonds by sorting through tons of sand that, literally, stretched as far as the eye could see. Yields of commercially viable stones began to diminish following World War I, however, and in 1956 the town was abandoned. Some of the industrial buildings and machine shops have been partially restored, but the run-down homes remain and are open to visitors; Photos 16 and 17 show the condition of several of these.

Two plants of particular interest occur in the town site, one a member of the Asteraceae and the other a second species of Sarcocaulon. In Photo 17 the compact, grayish shrub scattered about, and seen more clearly in the close-up in Photo 18, is Didelta carnosa var. tomentosa. Two varieties are recognized, D. carnosa var. carnosa, and D. carnosa var. tomentosa, so-named because of the presence of white hairs on its leaves. The genus consists of only two species, D. carnosa just mentioned, and D. spinosa, which we will meet in a later article. The second noteworthy plant in this otherwise desolate area is Sarcocaulon patersonii (Photo 19), which grows in open sand plains and in cracks in rocks, as seen here.

quiver tree
Photo 20. A single quiver tree at the Fish River Canyon, Namibia.
quiver trees
Photo 21.  Quiver trees at Augrabies Falls National Park, South Africa.
Aloe dichotoma var. dichotoma
Photo 22. A forest of Aloe dichotoma var. dichotoma, quiver trees, or kokerbom in Afrikaans.
Aloe dichotoma var. dichotoma
Photo 23. Aloe dichotoma trees at sunset, with a photographer shown for scale.
Aloe dichotoma var. dichotoma
Photo 24. A close-up of the attractive, scaly bark of Aloe dichotoma.

The next plant is one that immediately stands out as something rather special, one of the tree aloes. Most readers will be familiar with ‘aloe,’ a generic term for plant preparations used as constituents of some medical formulations and skin care products. These preparations are derived from some members of a genus of the same name; Aloe consists of about 365 species with a large percentage of them native to southern Africa (others occur in Madagascar, the Canary Islands, and the Arabian peninsula).

Although occasionally seen in the literature as constituting the family Aloaceae (= Aloeaceae), the genus is generally considered as part of the Asphodelaceae (the type genus is Asphodelus), where its distinctiveness is recognized at the subfamily level: Alooideae (along with the succulent genera Gasteria and Haworthia).

One of the most striking of the southern African tree aloes is Aloe dichotoma var. dichotoma, which enjoys a distribution in Namaqualand and Bushmanland ranging from Nieuwoudtville north into Namibia and east to Upington and Kenhardt. This slow growing species, which flowers in July—we missed flowers by three weeks—occurs in extremely arid habitats, often as single individuals such as seen in Photo 20, taken near the Fish River Canyon in Namibia, or as a small cluster as shown in Photo 21, which was photographed in the Augrabies Falls National Park in South Africa. Some ‘forests’ of A. dichotoma do exist, however. One of these, the Quiver Tree Forest at Garigarus Farm near Keetmanshoop, Namibia, consists of about 250 trees and is a regular stop on the tourist route (Photo 22). It is recommended that visits to this site be timed to take advantage of the late afternoon light, as seen in the dramatic silhouette in Photo 23; note the size of a fellow-photographer for scale. A close-up of the bark of this attractive plant is shown in Photo 24.

Photo 25. Sunset in Namibia.

The Afrikaans name for this tree is “kokerboom,” which is where the English name quiver (= koker) tree (= boom) comes from. Indigenous peoples (the San) cut lengths of stem of the plant, hollowed them out, and fitted animal skins over the ends to make quivers for their poisoned arrows. The Bushman name for the plant is ”choje.”

It seems only fitting that since we have spent our time in Namibia that we should close out with a Namibian sunset (Photo 25). We hope you enjoyed the desert visit. Sleep well.

Bruce A. Bohm January 21, 2008

Literature cited…


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