ERIOSPERMUM ERINUM, ERIOSPERMUM PUSTULATUM, ORNITHOGALUM ADSEPTENTRIONESVERGENTULUM AND STRUMARIA BIDENTATA FROM THE NORTHERN CAPE.
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SUMMARY.
Eriospermums are widespread in South Africa and Namibia with the most unusual and interesting species found in the Northern Cape and adjacent parts of the western Cape. Two species Eriospermum erinum and Eriospermum pustulatum have very attractive foliage and unusual adaptations to their harsh environments. There is a detailed discussion of these plants in their habitats in the newsletter.
Ornithogalum adseptentrionesvergentulum was described in December 1996. It is a unique species adapted to growing in grey shale gravel where its tuft of cryptic foliage 1 – 2 cms tall is very difficult to see. There is an account of these plants in the newsletter and how they survive in their harsh environment.
Strumaria bidentata grows in stabilised sand in the windswept desert on both sides of the Orange River close to its mouth. These plants have some very interesting adaptations to their hostile environment. There is an account of these Strumarias in the newsletter.
NEWSLETTER.
Eriospermum erinum is found in a small area south of Nieuwoudtville usually growing on clayey soil amongst karooid shrubs. The type description of the plant was published by Pauline Perry in the South African Journal of Botany in 1989. The Eriospermums were originally collected on the farm Lokenberg which is probably the southern end of the distribution range. In more recent times the plants have been found further north in the area near the farm Papkuilsfontein. Overall the plants are rather rare and sparsely distributed and absent from a good deal of apparently suitable habitat.
Eriospermum pustulatum was found a long time ago in 1940 near Sutherland. It is amongst the rarest of the Eriospermums and is known from very few collections. Recent records are from the vicinity of Sutherland in an area which experiences temperatures well below 0° Celsius on many winter nights.
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 The leaves of Eriospermum erinum are diagnostic and amongst the most ornamental produced by species in the Genus Eriospermum. |
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 The leaves of Ornithogalum adseptentrionesvergentulum match almost perfectly the shale gravel in which they grow. |
 Strumaria bidentata grows in stabilised coastal desert sand often amongst wind worn pebbles. |
 The leaves of Strumaria bidentata often have conspicuous red margins. Their leaf surfaces are somewhat viscous causing particles of sand to cling to them. |
ERIOSPERMUM ERINUM.
E. erinum shares its habitat with many other tuberous and bulbous plants, including other Eriospermum species. The undulating karooid scrub country where the plants grow is stocked with sheep throughout and a good proportion of the habitat has been destroyed for wheat fields. Sheep do a good deal of damage to the small rather delicate leaves and consequently the plants grow well within the shelter of shrubs where they are protected from the hooves of grazing animals.
The Eriospermums thrive in areas where grazing domestic stock is excluded and in this respect road reserves play an important role in conserving the plants. The species may at times be locally well represented in some road reserve areas, particularly if the area between the road and the farm boundary fence is
fairly broad. The plants in the road reserves are probably a good indication of what the distribution of the species must have been like prior to the advent of
widespread sheep farming in the region. In these places the tubers grow within the shelter of shrubs, as they do on farmland stocked with sheep and also out in the open in direct sunlight. Populations consist of scattered individual plants and a few small groups of tubers usually 3 – 5 growing in an area of about 30 square centimetres. There are always good numbers of young plants in the road reserve populations.
The enations on the leaves of this species may be spectacular and dense as with the specimen featured in the photographs accompanying the text. They may also be few and widely spaced. It is possible that this species may hybridise with Eriospermum capense which is common throughout the area where E. erinum grows. Likely instances of this are when plants with large leaves are found bearing few enations. Further research is required and it may then be found that the leaf sizes and enations are very variable in this species. The leaves of juvenile plants are covered in enations well before they reach flowering size.
The E. erinum tubers are very small usually about 1.5 x 1.5 cms in size. They are however well protected from desiccation in the hot dry summer as the clay in which they grow dries out like plaster of Paris. During the rainy western Karoo winter the water retentive clayey soil is usually moist for long periods after rainfall.
ERIOSPERMUM PUSTULATUM.
E. pustulatum has amongst the most beautiful and unusual leaves of any South African plants. The leaf surfaces are covered with numerous closely spaced pustules each bearing a stiff ivory coloured bristle. In the literature the bristles are recorded as golden in colour (Perry 1994: 179, Manning, Goldblatt, Snijman (2002: 152 – 153). The species is apparently rarely encountered and the populations very small usually consisting of single widely scattered tubers or else a few plants growing close together amongst rocks and karooid scrub.
The main distribution area seems to be around Sutherland which has the coldest winter temperatures in South Africa. The area receives most of its rainfall in the autumn and winter months and the plants generally grow in sticky red clay. This substrate retains water for long periods after rainfall and in consequence the tubers remain moist throughout the winter growing season. At one locality near Sutherland the plants are found on a gentle east-facing slope of a large hill, near the summit. They grow amongst rounded dolerite boulders and under low shrubs. They are exposed to direct sunlight where they grow around boulders but are lightly shaded for most of the day when they occur within the shelter of karooid shrubs.
The E. pustulatum may grow close to Eriospermum capense. This plant is extremely common at the locality referred to near Sutherland. It occurs in a different niche however frequenting hill slopes mostly lacking shrubs and cobbled with dolerite pebbles and boulders. No hybrids between the two species have been seen and they are likely to have different flowering times.
In the summer months the clay in the E. pustulatum habitat dries out like cement completely protecting the large fleshy tubers against desiccation. The region where the Eriospermums grow is used extensively for sheep farming and the leaves are frequently damaged by the hooves of the grazing animals where the plants occur in the open. The presence of the sheep is likely to restrict the occurrence of most tubers to places adjacent to rocks or boulders or else under shrubs. In these situations they are well protected from the hooves of grazing animals.
The rarity of E. pustulatum seems to be linked to the fact that plants flower rather irregularly and that individual tubers may not produce flowers for a few successive seasons. Little is currently known about this beautiful unusual plant and its natural history is an enigma.
ORNITHOGALUM ADSEPTENTRIONESVERGENTULUM.
O. adseptentrionesvergentulum was described by Ute and Dietrich, Müller- Doblies in 1996 (1996: 446 – 449). The Latin name may be translated as “the little chap inclined towards the north” and refers to the fact that the greenish black cluster of subterete leaves usually inclines to the north or north west. The main area inhabited by this species seems to be the area to the north and north west of Laingsburg.
The leaves, which often have a soft silvery pubescence match almost perfectly the grey shale gravels in which the plants occur. The colour of the gravel varies from light to dark grey and the plants are always cryptic and easily overlooked. The habitat is very specific and sparsely colonised by a few species in other genera. Amongst these are Brunsvigia comptonii, a Bulbine species with cryptic blackish leaves that appears to be undescribed, Lachenalia comptonii and Lithops comptonii.
The Ornithogalums only sprout leaves after good rainfall and it is probable that several dry years pass in succession without the bulbs breaking dormancy. The plants are absent
from a great deal of suitable habitat particularly in places stocked with sheep and goats. Here the exposed leaves
are readily damaged or destroyed by the hooves of grazing animals. The habitat niche where the Ornithogalums are found is very harsh. It is exposed to intense direct sunlight during the summer months and the bulbs need to resist high ground temperatures. In the winter growing season night temperatures may regularly drop to 0° Celsius or lower. The bulbs avoid frosty valleys preferring shale outcrops at the bases of low hills.
The plants are usually rather rare occurring in small scattered groups. They are generally concentrated at the edges of little runnels in the shale which retain moisture for longest after rainfall.
In recent times the Ornithogalums have been found in good numbers on shale bands near Matjiesfontein further westwards from the area north of Laingsburg, originally prospected by the Müller-Doblies. The habitat near Matjiesfontein is full of depressions and runnels amongst the shale gravel providing optimum numbers of niches for the bulbs to colonise. This habitat is much more rich in niches than the shale areas north of Laingsburg which tend to be uniform, either flat or gently sloping.
STRUMARIA BIDENTATA.
S. bidentata has adapted to a very harsh habitat of stabilised desert sand on both sides of the Orange River near its mouth. The distribution of the species lies in the extreme north western corner of South Africa and the adjacent part of Namibia, across the Orange River. The habitat is exposed to continual strong winds during the summer months. At this time of the year however the bulbs are dormant. During the autumn and winter the temperatures are mild and the winds less frequent in duration and velocity. S. bidentata flowers in early May when the plants are in a leafless state. They set seed from the middle of May to early June at a time when heavy fog is blown inland from the nearby Atlantic Ocean. The fog falls as soft penetrating rain assisting the seeds with germination by damping the sand on which they fall.
The Strumarias sprout leaves well after the plants have flowered and set seed, usually in the second half of June and early July. This is often the time of the year when cold fronts bring some rain to this coastal desert. The bulbs do not usually produce leaves unless the desert in which they grow is well moistened by a few good rain showers. The plants may remain dormant during dry years and during these times they tend not to flower. The best flowering usually occurs in the autumn following a previous season of good rainfall. At these times a great deal of seed may be liberated into the environment and seedling bulbs are recruited to the populations should there be follow up rains during the winter months.
The habitat niche occupied by the Strumarias consists of flat or gently sloping stony areas where there is little major movement of sand during times of prolonged winds. These are also places which preserve moisture near the surface, where the bulbs grow, for the longest periods after rainfall.
REFERENCES.
John Manning, Peter Goldblatt and Dee Snijman. The Colour Encyclopedia of Cape Bulbs. Timber Press, Portland, Oregon, U.S.A. 2002: 145 – 154.
Ute and Dietrich Müller-Doblies. Revisionula incompleta Ornithogalorum Austro-Africanorum (Hyacinthaceae). Feddes Repertorum, Berlin, Germany, 107 (1996), 5 – 6.
Pauline L. Perry. A Revision of the Genus Eriospermum (Eriospermaceae), Contributions from the Bolus Herbarium, Number 17, National Botanical Institute, Claremont, 7700, Cape Town, South Africa. October, 1994.
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