South Arica's Uncommon Plant Families
In the early 19th century botanists attempted to organize the earth’s flora into a system that reflected overall patterns of geographic distribution. The result was a set of floral kingdoms, subkingdoms, regions, and provinces. A recent reworking of the early system by the Russian botanist Armen Takhtajan (1969 in translation) has seven Kingdoms, some of the larger ones of which are further split into Subkingdoms, and 37 Regions. The richness of the South African flora inspired earlier workers—and echoed by Takhtajan—to recognize the “Cape Floral Kingdom,” to which I made reference in an earlier article. A recent re-examination of the subject by C. Barry Cox, retired biogeographer from King’s College, London, however, led to a reassessment of many of the earlier conclusions, including whether the Cape flora deserves recognition at the highest level. His conclusion was that it does not, suggesting instead that it be recognized at the level of Region within the African Kingdom (formerly part of the Palaeotropical Kingdom). One of the reasons for the original assignment of Kingdom status for the Cape was the shear number of endemic families, genera, and species that occur there. Estimates of species numbers range from a conservative 8,000 to nearly 9,600, some 70% of which are endemic. The earlier workers were equally impressed—overwhelmed might be a more appropriate word—by the concentration of species that occur within the very limited area of the Cape. More recent appraisals have pointed out that other areas of diversity approaching that of the Cape are well known, and include, for example, southwestern Australia and western Asia. These were considered Regions, more or less, in the earlier treatments.
It has also become obvious on the basis of much recent study that the Cape flora is not unique when the region is considered in relation to other regions of similar climatic conditions (R. M. Cowling et al. 1996). Thus, cool wet winters and warm dry summers are also characteristic of the climates of California, central Chile, southwestern Australia, and the Mediterranean Basin. These five Mediterranean-climatic regions occupy about 5% of the earth’s surface, but are home to some 48,250 species of vascular plants, including high levels of taxa unique to each area, i.e., endemics.
This article will describe a small selection of the Cape Floral Region’s unusual plant families that Lesley and I were fortunate to encounter on our journeys. Two of the families, Bruniaceae and Penaeaceae, are endemic. The others, Melianthaceae, Neuradaceae, and Restionaceae, have significant representation in the Cape flora, but have members elsewhere. Details of plant families endemic to or centered in southern Africa can be found in an article of that title by R. Dahlgren and E. van Wyk (1988).
Bruniaceae are a moderate sized family, 74 or 75 species in 12 genera, endemic to South Africa. All species but one are restricted to sandstone in the Cape area; the outsider, Raspalia trigyna, known from Natal and Pondoland, was known from a single surviving individual at the time Dahlgren and van Wyk wrote their paper in 1987. Photo 1 features Brunia laevis a species that occurs only in the extreme southwestern Cape area. A representative of the genus Nebelia (some consider this a synonym of Brunia) is seen in Photo 2, which we identified as N. paleacea. Many brunias cover large areas, especially in damper areas such as the field we passed a few km north of the Cape of Good Hope (Photo 3), and a hillside seeps we saw in the Fernkloof Nature Reserve (Photo 4).
Although Bruniaceae are considered a well-supported family, DNA data, did not yield strong support for identifying close relatives, although the small South American Columelliaceae was indicated as a possibly related family. Earlier, pre-DNA-based, opinion had Bruniaceae as one of a group of woody families related to Saxifragaceae. Problems of this sort—when dealing with DNA data—can often be the result of insufficient sampling of genera. In the case of Bruniaceae, only two of the dozen genera recognized have been studied—Berzelia and Brunia—but never in the same study. DNA data referred to in this article come from a major treatise on phylogeny and evolution of angiosperms by D. E. Soltis et al. (2005).
Melianthaceae consist of two genera, Melianthus and Bersama, with a total of eight species. All six species of Melianthus occur only in South Africa; Bersama has a bit wider distribution with one of its species known from tropical Africa. Melianthus major (Photo 5) is a fairly widespread plant that grows mostly along streams in much of the southwestern Cape and in appropriate habitats along the southern coast. It is a large, rather fetid plant here seen in relation to one of our driver/guides. A species endemic to Namaqualand is Melianthus pectinatus (Photo 6), which can be found growing on dry rocky slopes.
DNA data put Melianthaceae in a group of families with Geraniaceae; this relationship is not as clearly seen when morphological data are compared. Some earlier workers suggested a relationship with woody members of Saxifragaceae.
Neuradaceae consist of three genera encompassing nine species. Neurada is a monotypic genus that occurs from the eastern Mediterranean to the Indian deserts. Neuradopsis consists of three species restricted to southwestern Africa, while Grielum, the genus of interest here, consists of five species. Grielum humifusum occurs widely in Namaqualand, offering attractive shows of its two-tone flowers, yellow with a white center (Photos 7 and 8).
The brownish fruits of this species have papery lobes as seen in Photo 9. The roots of G. humifusum are edible but slimy, an unpleasant feature that might be suggested by one of its Afrikaans names, “pietsnot.” Despite this feature, the roots are apparently a delicacy to duikers (Sylvicarpa grimma, a small antelope) leading to the less distasteful Afrikaans name “duikerwortel.” A closely related species, G. grandiflorum, occurs along the coastal plain of Namaqualand and other sandy areas of the Western Cape. It has sulphur-yellow flowers that lack the white center of its inland relative. Three other species of Grielum are known.
DNA data put Neuradaceae as sister group to a collection of families in Malvales including, Bixaceae, Malvaceae, and Thymelaeaceae.
Penaeaceae are a small family all members of which are restricted to the Cape Floral Region. The family consists of 21 species allocated to seven genera (one authority says six). The type genus, Penaea, consists of four (or an even dozen if one includes Stylapterus (some authorities combine the two). During our much too short stop in the Hermanus area (an hour’s drive east of Cape Town) we visited the Fernkloof Nature Reserve, an 1800 hectare preserve that lies in the Kleinrivier Mountains. Among the amazing plants to be found in this stand of coastal fynbos are several members of the Penaeaceae, among them the monotypic genus Saltera. Saltera sarcocolla is shown in Photos 10 and 11. Other members of the family have similar ericoid (resembling Erica in the Ericaceae) growth form, but differ in details of floral structure.
DNA analysis of members of Penaeaceae place the family within a large assemblage of families within the order Myrtales. The most closely related family, the sister group in the current language, are Oliniaceae, which consists of the sole genus Olinia, with species in East Africa, South Africa, and on the mid-Atlantic island St. Helena.
Restionaceae, one of the major contributors to the Cape monocotyledonous flora, are a difficult family to handle, especially for a first-time visitor to southern Africa. In addition to the considerable variation within and among groups—there are 180 species in 10 endemic genera in the Cape Region alone—the plants are dioecious (sexes on different individuals). Overall, the family consists of about 420 species in 41 genera with representatives in tropical Africa, Madagascar, a single species in Viet Nam, and a sizable representation in Australia. Although we saw several members of the family, reliable names eluded us. So, the plants in the following illustrations are simply identified as restios, the common term for members of the family.
DNA data place Restionaceae firmly within a group of families, including Poaceae (the grasses), that Soltis et al. (2005) refer to as constituting the “Core Poales.” I have heard the restios referred to commonly as Cape grasses, which is misleading because true grasses, constituting the family Poaceae, are also well known in the African flora.
Bruce A. Bohm February 14, 2008
Several of the major sources used for preparation of this article are listed below so that interested readers may delve further into the subject should they wish. The going is not easy, but can be rewarding.