A synoptic review of the aloes (Asphodelaceae, Alooideae) of KwaZulu-Natal, an ecologically diverse province in eastern South Africa.

The KwaZulu-Natal province of South Africa has a varied topography, geology and climate and presents diverse habitats that support a rich and diverse flora. Aloes are well represented in KwaZulu-Natal, with four genera [Aloe L., Aloiampelos Klopper & Gideon F.Sm., Aloidendron (A.Berger) Klopper & Gideon F.Sm. and Aristaloe Boatwr. & J.C.Manning] and 49 taxa occurring in the province. Fourteen of these are endemic and eleven near-endemic to the province. A floristic treatment of the aloes of KwaZulu-Natal is presented in the form of a synoptic review. Included are an identification key to the aloes that occur naturally in the province, species-level distribution maps and accompanying images, so providing for the first time, an atlas of aloe occurrence in this part of the subcontinent.

Temperature controls phenology in continuously flowering Protea species of subtropical Africa.

PREMISE OF THE STUDY: Herbarium specimens are increasingly used as records of plant flowering phenology. However, most herbarium-based studies on plant phenology focus on taxa from temperate regions. Here, we explore flowering phenologic responses to climate in the subtropical plant genus Protea (Proteaceae), an iconic group of plants that flower year-round and are endemic to subtropical Africa. METHODS: We present a novel, circular sliding window approach to investigate phenological patterns developed for species with year-round flowering. We employ our method to evaluate the extent to which site-to-site and year-to-year variation in temperature and precipitation affect flowering dates using a database of 1727 herbarium records of 25 Protea species. We also explore phylogenetic conservatism in flowering phenology. RESULTS: We show that herbarium data combined with our sliding window approach successfully captured independently reported flowering phenology patterns (r = 0.93). Both warmer sites and warmer years were associated with earlier flowering of 3-5 days/°C, whereas precipitation variation had no significant effect on flowering phenology. Although species vary widely in phenological responsiveness, responses are phylogenetically conserved, with closely related species tending to shift flowering similarly with increasing temperature. DISCUSSION: Our results point to climate-responsive phenology for this important plant genus and indicate that the subtropical, aseasonally flowering genus Protea has temperature-driven flowering responses that are remarkably similar to those of better-studied northern temperate plant species, suggesting a generality across biomes that has not been described elsewhere.

Foliar secretory structures in Ekebergia capensis (Meliaceae).

Ekebergia capensis is a medium-sized to large evergreen to deciduous tree ranging from southern Africa to Ethiopia. Two morphologically-distinct variants of E. capensis, southern and northern, may be recognized in southern Africa. Despite its wide distribution range there appear to be no published reports on the secretory structures occurring on the leaves. In very young leaves, colleters on the petiolules, adjacent portions of the rachis and the midrib of the adaxial leaflet surfaces, secrete fluid which at least partly covers these developing areas. This is the first record of colleters in Meliaceae. In addition, several extrafloral nectaries (EFNs) are found in variable positions on the abaxial side of the leaflets. No stomata are associated with the EFNs. The glandular tissue of active EFNs is surrounded by druse crystals of calcium oxalate and consists of secretory cells some of whose walls are separated by "strands" of amorphous lipophilic material, especially in a radial orientation. EFNs on developing leaves are inconspicuous but with time, frequently become more easily visible due to the accumulation of pinkish/reddish anthocyanins. Even on senescent leaves, shed in autumn, large droplets of nectar are frequently visible on the EFNs. The secretory tissue originates from protoderm and ground tissues. Slight differences in abundance, size, shape, position and structure exist between the EFNs of the southern and northern forms. Varying proportions of glucose, fructose and sucrose were detected in the rather viscous nectar with the most abundant sugar usually being fructose. Ants were only rarely observed feeding on the nectar. This finding is in conflict with the generally accepted idea that EFNs provide food for ants which in turn protect the plant from herbivores. More detailed studies of the chemistry of the nectar, which is relatively copious, may provide clues as to the function.

Diversity and biogeographical patterns of legumes (Leguminosae) indigenous to southern Africa.

The principal aim of this study was to establish biogeographical patterns in the legume flora of southern Africa so as to facilitate the selection of species with agricultural potential. Plant collection data from the National Herbarium, South Africa, were analysed to establish the diversity and areas covered by legumes (Leguminosae/Fabaceae) indigenous to South Africa, Lesotho and Swaziland. A total of 27,322 records from 1,619 quarter degree grid cells, representing 1,580 species, 122 genera and 24 tribes were included in the analyses. Agglomerative hierarchical clustering was applied to the presence or absence of legume species in quarter degree grid cells, the resultant natural biogeographical regions (choria) being referred to as leguminochoria. The description of the 16 uniquely formed leguminochoria focuses on defining the associated bioregions and biomes, as well as on the key climate and soil properties. Legume species with a high occurrence in a leguminochorion are listed as key species. The dominant growth form of key species, species richness and range within each leguminochorion is discussed. Floristic links between the leguminochoria are established, by examining and comparing key species common to clusters, using a vegetation classification program. Soil pH and mean annual minimum temperature were found to be the main drivers for distinguishing among legume assemblages. This is the first time that distribution data for legumes has been used to identify biogeographical areas covered by leguminochoria on the subcontinent. One potential application of the results of this study is to assist in the selection of legumes for pasture breeding and soil conservation programs, especially in arid and semi-arid environments.

Evolutionary history and leaf succulence as explanations for medicinal use in aloes and the global popularity of Aloe vera.

BACKGROUND: Aloe vera supports a substantial global trade yet its wild origins, and explanations for its popularity over 500 related Aloe species in one of the world's largest succulent groups, have remained uncertain. We developed an explicit phylogenetic framework to explore links between the rich traditions of medicinal use and leaf succulence in aloes. RESULTS: The phylogenetic hypothesis clarifies the origins of Aloe vera to the Arabian Peninsula at the northernmost limits of the range for aloes. The genus Aloe originated in southern Africa ~16 million years ago and underwent two major radiations driven by different speciation processes, giving rise to the extraordinary diversity known today. Large, succulent leaves typical of medicinal aloes arose during the most recent diversification ~10 million years ago and are strongly correlated to the phylogeny and to the likelihood of a species being used for medicine. A significant, albeit weak, phylogenetic signal is evident in the medicinal uses of aloes, suggesting that the properties for which they are valued do not occur randomly across the branches of the phylogenetic tree. CONCLUSIONS: Phylogenetic investigation of plant use and leaf succulence among aloes has yielded new explanations for the extraordinary market dominance of Aloe vera. The industry preference for Aloe vera appears to be due to its proximity to important historic trade routes, and early introduction to trade and cultivation. Well-developed succulent leaf mesophyll tissue, an adaptive feature that likely contributed to the ecological success of the genus Aloe, is the main predictor for medicinal use among Aloe species, whereas evolutionary loss of succulence tends to be associated with losses of medicinal use. Phylogenetic analyses of plant use offer potential to understand patterns in the value of global plant diversity.

Oberholzeria (Fabaceae subfam. Faboideae), a new monotypic legume genus from Namibia.

Oberholzeria etendekaensis, a succulent biennial or short-lived perennial shrublet is described as a new species, and a new monotypic genus. Discovered in 2012, it is a rare species known only from a single locality in the Kaokoveld Centre of Plant Endemism, north-western Namibia. Phylogenetic analyses of molecular sequence data from the plastid matK gene resolves Oberholzeria as the sister group to the Genisteae clade while data from the nuclear rDNA ITS region showed that it is sister to a clade comprising both the Crotalarieae and Genisteae clades. Morphological characters diagnostic of the new genus include: 1) succulent stems with woody remains; 2) pinnately trifoliolate, fleshy leaves; 3) monadelphous stamens in a sheath that is fused above; 4) dimorphic anthers with five long, basifixed anthers alternating with five short, dorsifixed anthers, and 5) pendent, membranous, one-seeded, laterally flattened, slightly inflated but indehiscent fruits.

The epidermal cell structure of the secondary pollen presenter in Vangueria infausta (Rubiaceae: Vanguerieae) suggests a functional association with protruding onci in pollen grains.

Secondary pollen presentation is a well-known phenomenon in the Rubiaceae with particularly conspicuous pollen presenters occurring in the tribe Vanguerieae. These knob-like structures are formed by a modification of the upper portion of the style and stigma, together known as the stylar head complex. In the flower bud and shortly before anthesis, the anthers surrounding the stylar head complex dehisce and release pollen grains which adhere to the pollen presenter. The epidermal cells of the pollen presenter facing the anthers are radially elongated with a characteristic wall thickening encircling the anticlinal walls of each cell towards the distal end. These cells were studied in the pollen presenter of Vangueria infausta using electron and light microscopy in conjunction with histochemical tests and immunohistochemical methods. Other prominent thickenings of the cell wall were also observed on the distal and proximal walls. All these thickenings were found to be rich in pectin and possibly xyloglucan. The terms "thickenings of Igersheim" and "bands of Igersheim" are proposed to refer, respectively, to these wall structures in general and those encircling the anticlinal walls of each cell near the distal end. The epidermal cells have an intricate ultrastructure with an abundance of organelles, including smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria and secretory vesicles. This indicates that these cells are likely to have an active physiological role. The pollen grains possess prominent protruding onci and observations were made on their structure and development. Walls of the protruding onci are also rich in pectin. Pectins are hydrophilic and known to be involved in the dehydration and rehydration of pollen grains. We hypothesise that the thickenings of Igersheim, as well as the protruding onci of the pollen grains, are functionally associated and part of the adaptive syndrome of secondary pollen presentation, at least in the Vanguerieae.

Structural evidence in Plectroniella armata (Rubiaceae) for possible material exchange between domatia and mites.

Domatia are small structures on the lower surface of a leaf, usually taking the form of cavities, pouches, domes with an opening, or hairs (or a combination of these), and located in the axils between the main veins. They are found in many dicotyledons including certain members of the Rubiaceae. As part of an ongoing study of selected southern African members of the tribe Vanguerieae of this family, their structure in transverse section was investigated. In some taxa, such as Plectroniella armata, light microscopic (LM) observations revealed large numbers of stomata in the domatia as well as a number of channel-like structures extending across the cuticle toward the cavity of the domatia. The cuticle of the epidermis lining the domatia also appeared thicker than in other parts of the leaves. The epidermis in P. armata was also examined using transmission electron microscopy (TEM). Domatia have been shown to house mainly mites, many of which are predatory or fungivorous, in a symbiotic (mutualistic) relationship with the plant. To date, much research has focussed on the role of domatia in providing shelter for various organisms, their eggs and their young. However, the TEM study revealed the apparent "channels" and thick cuticle seen under LM to be electron dense non-cellulosic branching fibrils within pronounced, often closely spaced cuticular folds. The functional significance of these fibrils and folds requires further investigation. Folding of cell walls and membranes at ultrastructural level is usually functionally associated with an increased surface area to facilitate active exchange of compounds/metabolites. This may indicate that translocation of substances and/or other forms of communication is possible between the domatium and its inhabitants. This therefore suggests a far more active role for the leaf in the symbiotic relationship than was previously thought. More work is required to test such a possibility.

Alien phytogeographic regions of southern Africa: numerical classification, possible drivers, and regional threats.

The distributions of naturalised alien plant species that have invaded natural or semi-natural habitat are often geographically restricted by the environmental conditions in their new range, implying that alien species with similar environmental requirements and tolerances may form assemblages and characterise particular areas. The aim of this study was to use objective numerical techniques to reveal any possible alien phytogeographic regions (i.e. geographic areas with characteristic alien plant assemblages) in southern Africa. Quarter degree resolution presence records of naturalised alien plant species of South Africa, Lesotho, Swaziland, Namibia and Botswana were analysed through a divisive hierarchical classification technique, and the output was plotted on maps for further interpretation. The analyses revealed two main alien phytogeographic regions that could be subdivided into eight lower level phytogeographic regions. Along with knowledge of the environmental requirements of the characteristic species and supported by further statistical analyses, we hypothesised on the main drivers of alien phytogeographic regions, and suggest that environmental features such as climate and associated biomes were most important, followed by human activities that modify climatic and vegetation features, such as irrigation and agriculture. Most of the characteristic species are not currently well-known as invasive plant species, but many may have potential to become troublesome in the future. Considering the possibility of biotic homogenization, these findings have implications for predicting the characteristics of the plant assemblages of the future. However, the relatively low quality of the dataset necessitates further more in-depth studies with improved data before the findings could be directly beneficial for management.

Monitoring mercury in two South African herbaria.

Mercury [Hg] emissions from old plant collections treated with mercuric chloride (HgCl(2)) may present a high health risk for staff working in certain herbaria. The present study evaluated Hg concentrations in ambient air, plant specimens and biological samples from staff working in the Pretoria National Herbarium (PRE) and the H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria. Biological samples from a group of 15 people exposed to HgCl(2) in herbaria and a non-exposed control group of five people were studied. Additionally, plant samples from herbarium specimens treated and non-treated with HgCl(2) were analysed. Plant materials treated with HgCl(2) had persistent high concentrations of Hg in the range of 114-432 microg g(-1), whereas untreated materials were in the range of 0.20-0.45 microg g(-1). The HgCl(2)-treated plant specimens induced elevated concentrations of Hg into the herbarium rooms near storage cabinets, where up to 1 microg m(-3) of Hg was measured in the air of both herbaria. However, no significant difference in mean Hg concentrations in hair was found between herbarium workers and members of the control group, 0.46 and 0.64 microg g(-1) respectively (p0.05, Student's t-test). For both groups, Hg concentrations were lower than that indicated by the World Health Organization [WHO] for non-exposed adults, namely 2 microg g(-1). The mean concentration of total Hg in urine from the mercury-exposed herbarium group, 2.28 microg g(-1) creatinine, was significantly higher than in the control group, 1.05 microg g(-1) of creatinine. For both populations, the concentrations of Hg in their urine were below the threshold Hg values set by the WHO, i.e., 5 microg g(-1) creatinine. We concluded that there was no strong response by individual herbarium staff from long-term exposure to Hg concentrations in the range of 0.28-1.1 microg m(-3).