Cultivated rooibos, Aspalathus linearis, near Graafwater. Photo: S. Gess
In the Clanwilliam area in spring the most obvious species is Aspalathus spinescens which cannot be missed as it produces an abundance of bright yellow pea-flowers and is massed on roadsides and sandy slopes. A less strikingly beautiful species, but one which is at the heart of a growing export and import industry, is Aspalathus linearis, rooibos: one of our few indigenous crops. Planted in serried ranks it is a familiar sight in the Clanwilliam/Graafwater districts, the centre of production. It was the indigenous inhabitants of the Cederberg who first discovered the pleasure of drinking an infusion made from the leaves of A. linearis. It was first commercially exploited in 1904 when its market potential was recognized by Benjamin Ginsberg, a Russian immigrant descended from a family who had been in the tea industry in Europe for centuries. He started buying the 'tea' from people in the Cederberg and selling it. By 1930, Frans Nortier, a medical doctor, had discovered its value as an agricultural product. My interest in Aspalathus has been centred on the flowers which offer rich rewards of nectar. As with all pea-flowers the nectar is not readily available to all comers. The flowers are structured in such a way that only potential polli ROOIBOS nators should be able to reach the nectar and in doing so, trigger the REFRESHMENT FOR HUMANS, BEES AND WASPS opening of the keel and the deposition of pollen on the visitor The flower visitors and pollinators ofAspalathus. which will unknowingly carry it to another flower of the same by Sarah Gess, Albany Museum, Grahamstown species with a receptive stigma where it will be placed. Although spalathus is the largest in the occurrence of Aspalathus on some days honeybees may be genus of flowering plants species, apparently due, in part at seen in large numbers on the A restricted to South Africa, least, to the different soil require flowers, they do not pollinate with about 278 species. The ments of each species. Most are them but rob them as they are able greatest species diversity is in the shrubs and do not exceed 2 m in to obtain nectar illicitly from the winter rainfall region but a few height. The genera Aspalathus, side without tripping the flowers species are found in the Eastern Lebeckia, Wiborgia and Rafnia so that they come away without Cape and KwaZulu-Natal. Most together constitute the Cape Group receiving pollen for transfer. The grow in fynbos, renosterveld and of the Crotalarieae (sensu Polhill) visitors which have the potential strandveld. There is little overlap of the Papilionaceae family. to pollinate the flowers of
Veld &- Flora March 2000 19 Aspalathus from the Western Cape to the Eastern Cape, whatever the species, are solitary bees of the Megachilinae (Megachilidae), most notably several species of Chalicodoma and Spinanthidium, and of the Anthophorinae (Apidae), most notably several species of Xylocopa. These are readily distinguished from each other even by the most casual observer as the megachilids carry purpose fully collected pollen on the underside of the abdomen whereas the apids pack it onto their hind legs. In the Western Cape and eastwards to Willow more, pollen wasps (Vespidae: Masarinae) are included in the pollinators. These bees and the larger pollen wasps, two species of Ceramius, C. clypeatus and C. richardsi, all trip the flowers when they alight on the wing petals and reach into the flower to Above. The pollen wasp Ceramius clypeatus withdrawing from a flower of obtain the nectar. The keel opens Aspalathus spinescens. Photo: S. Gess and the insect receives a dollop Below left. The large pollen wasp, Ceramius clypeatus (legs omitted) of pollen far forward on its in nectar-drinking position. Right. The smaller pollen wasp, Masarina underside. As these insects familiaris (legs omitted) in nectar-drinking position. always alight in the same way this pollen will be carried by them to other flowers which, if the stigma is receptive, will be pollinated. The smaller pollen wasps, two species of Masarina, M. familiaris and M. hyalinipennis, have a different technique for entering the flowers. They alight on the I b standard and, as such a wasp reaches down and inserts its tongue at the base of the flower, the keel opens and the wasp IOmm receives a dollop of pollen on the front of its head. Again as these wasps always alight in the same way, this pollen will be carried by them to other flowers which, if the stigma is receptive, will be pollinated. to Aspalathus. They are therefore, where present, the It is clear that unlike some flowers that are most dependable visitors and therefore the most dependent on a single pollinator or a few related dependable pollinators. pollinators, Aspalathus is serviced by a relatively At least four of the Chalicodoma species require large number of species from several taxonomic mud to construct their cells, two species in cavities groups. As the distribution and nesting requirements and two in the open on stones. Ceramius clypeatus of these insects vary the species composition of the and Masarina familiaris, and in all probability complex varies too. The bees are all less dependent C. richardsi and M. hyalinipennis, require water for on the presence of Aspalathus as none of them is the excavation of their burrows, the cementing of restricted to foraging for nectar and pollen on these their subterranean cells and the construction of plants or indeed the Cape Crotalarieae as a whole. turrets which surmount their burrow entrances. The two species of Masarina are restricted to Cape These bees and wasps do not occur in areas of loose Crotalarieae but not to Aspalathus only. However, it sandy soil, or far from water or where the only seems that the two species of Ceramius are restricted available water is contained within steep walls with
20 Veld &' Flom March 2000 A scanning electron micrograph of the pro-sternum Portion of the head of the polJen wasp Masarina and base of the front legs of the pollen wasp jamiJiaris, showing the area of impact with the anthers Ceramius clypeatus showing the area of impact with (and thus the pollen) of Aspalathus spinescens. the anthers ofAspalatus spinescens. The pollen Below. Boxed area enlarged. grains can be clearly seen. Below. Boxed area (actual length of box =:' 0.57 mm). enlarged. (actual length of box = 0.57 mm). no seepage. The Spinanthidium species, however, Acknowledgements: Thanks are due to my co-worker Fred Gess; Harvard University are free from these restrictions as they construct their Press for permission to reproduce illustrations from The Pollen nest-cells from resins. Carpenter bees, Xylocopa Wasps: Ecology and Natural History ofthe Masarinae by Sarah species, excavate their burrows in dry plari't stems, K. Gess; Robin Cross of the Electron Microscopy Unit. Rhodes Un'iversity for taking the scanning electron micrographs; and the the smaller species in pithy stems and the larger 'Ones Foundation for Research Development for a running expenses grant. in woody stems. For them presence and abundabce is governed by the availability of suitable stems. Further reading: Gess, S.K. (1996). The Pollen Wasps: Ecology and Natural History So when Aspalathus is cultivated, as is A. linearis, of the Masarinae. Harvard University Press, Canlbridge, Mass. if good seed production is required, the needs of,.the Gess, S.K. and Gess, F.W. (1994). Potential polllinators of Polhills's potential pollinators must be taken into at'coun! J Cape Group of Crotalarieae (Fabales: Papilionaceae), with implications for seed production in cultivated rooibos tea. when siting seed plots. @ African Entomology 2(2), 97-106.
About the author Sarah Gess is an entomologist based at the Albany Museum. She was born in England of South African parents. The contrast between the known natural world of England and the vast unknown of South Africa was striking and stimulating to an inquiring mind nurtured in a family for whom walking and picnicking was an essential part of life. It was natural therefore to choose a career in botany (in which she has an M.Sc.) and entomology (in which she has a Ph.D.) and to find these two disciplines inseparable. For the past thirty years she and her co-researcher Fred Gess, for many years assisted by their three sons, have been studying and publishing on the aculeate wasps and bees of semi-arid and arid areas of southern Africa: in the Karoo Biome and associated arid savanna, dry fynbos and desertic areas. Field studies have been conducted from the Eastern Cape to the Western Cape and north wards through Namibia into Kaokoland, and comparative studies made in Arizona and Australia. Sarah's approach is holistic; however, her particular fields of interest are nesting and flower visiting behaviour. Resulting from her study is a catalogue of 13 500 flower visiting records for 850 species of wasps and bees visiting flowers of 38 plant families. Sarah is currently preparing this catalogue for publi cation together with an analysis and discussion. Her book The Pollen Wasps (Harvard University Press, 1996) was mentioned in the Sarah Gess investigating a wasp's nest in the"" southern Karoo. March 1999 issue of Veld & Flora on page 31. It is available through Photo: F. Gess. the Botanical Society's Kirstenbosch Shop at tel (021) 762 1621.
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