March 2007 Veld&Flora42

Surv iva l s t ra teg ies

“I will put thee in a cleft of the rock and will cover thee with my hand” Exodus [33:22]

In an earlier edition of Veld & Flora the klipblom (rock flower) from the Succulent Karoo in Namaqualand was featured by H. M. Steyn (September 2004). This soft, herbaceous plant, Colpias mollis, belongs to the snapdragon family (Scrophulariaceae). It has striking white flowers and is only known to grow in boulder crevices in the summer dry, semi-arid Northern Cape. Plants from specialized habitats such as these often display specialized adaptations, especially in their reproduction phase. Life on the cliffs is difficult, especially in semi-desert terrain. In the article, it was demonstrated how the klipblom’s flower stalk, after fertilization, bends away from the light towards the crevice where the seeds are released. The mother plant thus ensures that its seeds are safely deposited within the crevice. The deep crevices carry additional moisture that the plant exploits with its extensive network of roots.

There is another indigenous cliff dweller and chasmophyte

The remarkable Kaoko klipblom An expedition to the Kaokoveld in north-western Namibia and a unique cliff hanger with a surprising twist to its tale

(a plant that only occurs in crevices), the Limpopo klipblom, Stemodiopsis rivae, a herbaceous perennial from the same family, the flower stalks of which also bend towards the crev-ice after fertilization. The well-known Cymbalaria muralis, a little garden escapee from the Mediterranean that we often see growing on walls, has a similar seed dispersal strategy.

The Kaoko klipblom, Rogeria petrophila, is another remark-able chasmophyte with a unique dual seed dispersal strategy - the only known cliff dwelling plant in the world to employ such a strategy.

Collecting the Kaoko klipblomDuring an expedition to the Otjihipa mountains in the

Kaokoveld in 2002, during which we documented succulent and bulbous plants that occur on cliff faces in north-western Namibia, we observed a plant that looked superficially like a klipblom. The plant however was not in flower and its identity remained unknown. During another visit in January 2005, to co-incide with the rainy season, the Otjihipa Mountains east of Omuhunga were re-visited and this time the plant was

The Kaoko kliplom, Rogeria petrophila, in flower in a granite rock crevice in the Otjihipa Mountains of the Kaokoveld, Nambia. Photo: Ernst van Jaarsveld.

by Ernst van Jaarsveld, Kirstenbosch

March 2007 Veld&Flora 43

found in flower. We realized it belonged to the Pedaliaceae family – possibly a Rogeria. (Later it was identified by Braam van Wyk as Rogeria petrophila.) This plant, which I call the Koako klip-blom, is a perennial, soft, herbaceous, semi-trailing, fragile plant bearing semi-succulent, broadly heart-shaped, deep-ly toothed leaves with striking, large, funnel-shaped, cream flowers. Its fruit is a slender, flattened, tapering capsule containing tiny oblong seeds.

The Kaoko klipblom occupies similar granite fissures to the Namaqua klip-blom, but its preferred climate differs somewhat, being hot, tropical, summer rainfall, arid savanna. When the plants were collected, we noticed, apart from its normal stems, a network of threadlike branches and tiny spoon-shaped leaves growing from its base, which we could not fully explain. The original descrip-tion by Bernard de Winter, former direc-tor of the Botanical Research Institute in Pretoria (now SANBI) in Kirkia in 1961 was consulted. Bernard de Winter and Otto Leistner (former botanist and editor of various botanical papers and magazines) discovered this plant in the Otjihipa Mountains in 1957. Bernard de Winter in his description noted one specimen with threadlike branches, and also commented that it produced smaller capsules (with normal seed), as well as its normal capsules. He sus-pected a dual seed dispersal strategy, but was not certain of its function. A follow up visit to Otjihipa at the end of the rainy season in April 2005, revealed its secret.

The April 2005 Otjihipa expeditionThis expedition was sponsored by

the University of Pretoria’s Botany Department. Our main purpose was to locate an unnamed large Aloe observed earlier and now in flower (subsequently named Aloe kaokoensis by Van Jaarsveld, Swanepoel and Van Wyk in Bothalia), but Rogeria was also high on our priority list. It was at the end of the rainy season and we were assisted by Wessel Swanepoel (engi-neer and local botanist), his wife and Jacobus van Sijl. We were fortunate to fly from Windhoek in a small Desert Airlines Cesna aeroplane directly to Syncro Camp at Otjinhungwa on the Kunene River, arriving at about 10h30 where we were met by Koos Verwey. Syncro Camp is situated just west of Otjihipa Mountain and Koos took us to our destination: the western foot of the Otjihipa. The vegetation on the flats, the

Marienfluss, consists of vast, red, sandy flats with mopane, Colophospermum mopane, predominating, and the mus-tard-tree, Salvadora persica, also very prominent. Usually the red sandy flats are barren, but this time they were covered with a carpet of yellow grass after the good autumn rains. The ‘fairy rings’ (concentric rings of about 5 m in diameter caused by termites, called heuweltjies in South Africa) in this red sandy habitat are very characteristic of this landscape.

We ascended the steep western slope in very rocky and open terrain. Mopane was still dominant, but there were many other smaller trees especially the corkwoods (Commiphora). These beautiful trees are very sculptural and each has distinctive leaves and bark.

ABOVE: Usually the red sandy flats of the Marienfluss are barren, but are covered with a carpet of yellow grass after the good autumn rains. Photo: Dorothy Raine.

BELOW: The Kaokoveld, Namibia. Map: Sally Adam, Technodraft.

There was the bonsai-like oak-leaved corkwood (Commiphora wildii), the striking slender corkwood (C. virgata) with broad bands of peeling bark, the purple-stem corkwood (C. multijuga), satin-bark corkwood (C. tenuipetiolata), blue-leaved corkwood (C. glaucescens) and the large-leaved corkwood (C. anac-ardiifolia). Other prominent trees and shrubs included the hairy shepherds tree (Boschia tomentosa), Kaoko rhigo-zum (Rhigozum virgatum), Kaoko pork-bush (Ceraria longipedunculata) and the broad-leaved porkbush (C. cari-soana). The gifnoors (Euphorbia virosa) was also impressive with its succulent stemmed, thorny candelabra sculpture, as was the smaller succulent, Kalanchoe lanceolata.

It was autumn and as usual for

44 March 2007 Veld&Flora

What does that mean?

biennial A plant with a short lifespan of two years.chasmophyte A crevice plant, confined to rock habitats.cleistogamy Pollination and fertilization before the flower opens.extrafloral nectaries A nectary (for nectar excretion) found on a plant other than in the flower.herbaceous Plants that are soft and not woody. perennial A plant that lives for several years, not perishing after flowering and fruiting.

this region, very hot and exposed. Our ascent was slow, and we had to rest often in the shade of boulders or small trees, as our water reserves did not last long. We spotted our klipblom in flower from about 800 m above see level. It was quite common and occurred on all aspects of its cliff habitat, most of them unreachable. We took photographs and proceeded upward to the escarpment, taking notes of the vegetation. At the top of our ridge we spotted our aloe in full flower and collected the necessary material in order to have it formally described. It has conspicuous whitish grey-green leaves and erect, branched inflorescence.

We had planned to set up camp in a dry riverbed below the western peak of Otjihipa which should yield some water, but we struggled to find any water. After a long walk upstream, Wessel spotted a small pool half hidden at the side of a granite embankment. We camped on the sandy gravel bed of the main drain-age line next to a huge boulder.

The secrets of the Kaoko klipblom revealed

We spotted our klipblom as well as its two relatives (Rogeria bigibbosa and R. adenophylla), both erect, rigid annuals bearing spreading, funnel-shaped flow-ers and armored woody capsules, grow-ing in the dry riverbed below amongst other annual species. After our first night’s rest, I had lots of time to inves-tigate the klipblom in its habitat while Wessel examined Boschia and Maerua trees.

The scientific name of the Kaoko klip-blom is Rogeria petrophila, so named because ‘petra’ means rock, and ‘philus’ means loving in Greek. It only occurs in granite fissures, mostly out of reach on cliffs and boulders; but I was able to study the plant carefully without hav-ing to make use of ropes. The plants are quite different to the other rigid and erect Rogeria species They are soft, herbaceous and short-lived peren-nial or biennial, bearing short trailing branches up to about 30 cm long that have funnel-shaped, cream-coloured flowers. Its stem base is slightly swollen and well wedged in the crevice. I also noticed the threadlike basal branches and noticed how they entered the same and adjacent crevices. The ability of a stem to grow away from the light source towards the darkness as in this case, is termed ‘phototrophic negative’ where ‘phototropism’ means an orientation response towards light.

BELOW: The Kaoko kliplom in a granite rock crevice. The thread-like, modified branches can clearly be seen growing towards the crevice. Photo: Ernst van Jaarsveld.

RIGHT: Illustration of the Kaoko klipblom, Rogeria petrophila showing the plant in a crevice (top right), the plant in flower (top left) and the plant with the normal stem and fruiting cap-sule as well as the threadlike branches which grow away from the light source and into a crevice to deposit its own self-fer-tilized seed (centre right), the normal fruiting capsule (a) and seed (b), the modified thread-like branches and smaller fruit-ing capsule (c) and modified seed (d), and leaf (bottom right). Illustration: Lisa Strachan.

ABOVE: Rogeria petrophila in a hairline crevice. Note the oval shaped, green fruiting capsules to the left of the rock fissure. These are the result of the growth of the modified, thread-like branches ‘planting’ their self-fertilized seed in the crevice. Photo: Ernst van Jaarsveld.

45March 2007 Veld&Flora

Acknowledgements

I am grateful to Professor Braam van Wyk who sponsored the expedition to the Otjihipa Mountains and to Wessel Swanepoel and Kobus van Sijl for their companionship in the field. Also to Koos Verwey for his hospitality and help at Syncro Campsite in the Kaokoveld.

Although it was difficult to examine due to the nature of the narrow crevices and the fragile nature of the branches, it became clear what the function of these threadlike branches was. I stood amazed at what I saw. Bernard de Winter was right in his prediction of a dual fruiting, seed dispersal strategy. In one of the crevices, I managed to expose the small, flattened capsules deeply buried in the crevice, which I could also photograph. I wriggled out some of these flattened, oval to heart-shaped capsules (about 6-8 mm in length) and noted they had oblong-oval seed about 2.5-3 mm in length and slightly winged with only up to 5 seeds per capsule. The normal capsules on the arboreal ‘nor-mal’ stems in contrast are about 18-25 mm in length and tapering, and pro-duce large amounts of wind-dispersed seed (more than 50 per capsule).

A dual seed dispersal strategyThe Kaoko klipblom clearly ‘plants’

some of its seed deep within the crevice of the mother plant or adjacent crevices as a back-up system - an additional insurance policy. This is additional to the normal flowers, fruits and wind-dis-persed seed. The plant can thus afford to produce less, but larger seed, to deposit deep within the crevice. Should the mother plant die, the larger seed of its cloned offspring, already buried deep within the crevice, can germinate and grow into normal plants. The only difference between the two fruit types are that the normal seeds are produced following cross-pollination from adja-cent populations (out-crossing) whilst the small crevice capsule’s seed are the result of self-pollination, and thus pro-duce clones of the original plant.

How does this plant bear capsules without flowers? The threadlike branch-es were carefully examined and found to have tiny cleistogamous, self-pollinat-ing, inconspicuous flowers that remain unopened. These small, self-fertile flow-ers result in the smaller oval capsules that get safely deposited deep within the crevice. These capsules have fewer, but larger seeds. In addition to this duel dispersal strategy, the seeds are cov-ered with mucilage which is thought to help with anchoring the plant, as well as with its water uptake.

This plant is thus adapted to its life on the cliff face with a dual seed dispersal strategy – the first record in the world of this cliff dweller's dispersal strategy. It is long-term environmental pressure (aridity, disturbance etc.) which has led

to this remarkable adaptation. Where the Namaqua and Limpopo klipbloms and Cymbalaria only have a modified capsule orientation strategy, our Kaoko klipblom is a step ahead and appears to be the most advanced in comparison to other cliff-dwelling plants.

Extra-floral nectariesAt Kirstenbosch seed was sown and

a plant carefully examined. Seed ger-minated in December, and the young plants grew fast. Small, reddish extra-floral (i.e. away from and not in the flower) nectaries were observed in the leaf axils, situated between the flower stalk and petiole. Ants were seen vis-iting the nectaries so this is clearly a defence strategy employed by the flower to ward off plant eating insects. It lures ants by providing nectar, and uses the ants to attack unwanted visitors.

In dry habitats, succulent and suc-culent bulbous plants are prominent on cliff faces. This is not surprising, as their water storage ability enables them to survive in extreme, dry conditions that most herbaceous plants could not endure. Many of these succulents also

have a vegetative reproductive back-up system such a the production of bulbils in Cyrtanthus montanus, Ornithogalum juncifolium var. emsii, Oxalis fergusonae and O. pocockiae. Many of the members of the Crassulaceae such as Crassula setulosa var. jenkinsii have brittle veg-etative buds (or leaves in the case of Adromischus) that easily detach and root where they land in nearby cracks and crevices.

Plants, it seems, will go to extremes in their struggle to survive. Life on cliffs in a desert situation is not easy, but the Kaoko klipblom has evolved remarkable strategies to overcome its difficult envi-ronmental conditions and ensure its long-term survival.

ABOVE: The recently discovered and named Aloe kaokoensis from the western Otjihipa Mountains of Namibia.