Browsing by Author "Edwards, Trevor John."

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Bioprospecting the flora of southern Africa : optimising plant selections.
(2005) Douwes, Errol.; Edwards, Trevor John.; Crouch, Neil Robert.
Focused procedures which streamline and optimise plant prioritisation and selection in bioprospecting have the potential to save both time and resources. A variety of semiquantitative techniques were assessed for their ability to prioritise ethnomedicinal taxa in the Flora of Southern Africa (FSA) region. These techniques were subsequently expanded upon for application in plant selection for the Novel Drug Development Platform bioprospecting programme. Least squares regression analyses were used to test the hypothesis that ethnomedicinal plant use in southern Africa is strictly random, i.e. no order or family contains significantly more medicinal plants, than any other order or family. This hypothesis was falsified revealing several 'hot' plant orders. The distribution of southern African ethnomedicinal taxa was investigated, and revealed low ethnomedicinal plant usage in the Western Cape and Northern Cape. The historical settlement of Bantu tribes in the eastern regions of southern Africa was one explanation for this discrepancy. Growth forms of ethnomedicinal taxa in 'hot' orders (identified in the regression analysis) were analysed. The results indicated no clear preferences across orders, but rather a preference for particular growth forms in certain orders. With respect to distribution, endemism and Red Data List status of ethnomedicinal taxa, the Western Cape had the greatest proportion of endemics and Namibia had the highest proportion of Red Data Listed ethnomedicinal taxa. With respect to chemotaxonomy, the Asteraceae contained the highest proportion of terpenoids, the Rubiaceae the highest proportion of alkaloids and the Fabaceae the highest proportion of flavonoids. The predictive value of regression analyses was tested against an existing analysis of anti-malarials and the subsequent in vitro bioassays on Plasmodium falciparum. In particular, the ability of these analyses to identify plants with anti plasmodial IC50 values of [less than or equal to] 10 [micro]g/ml was assessed. Most species in 'hot' genera showed comparatively good antiplasmodial activities (IC50 [less than or equal to] 10 [micro]g/ml). Plant candidates were prioritised for screening anti-tuberculosis, anti-diabetes and immune-modulatory compounds, using a weighting system based on; their ethnomedicinal application, chemotaxonomic potential, frequency in ethnomedicinal trade, association with the relative disease, toxicity, Red Data status, indigenous or endemic status, and family selection in ethnomedicine (identified through regression analyses). Other taxa were short-listed due to their presence in biodiversity hotspots where few ethnomedicinal plant use records are documented, and still others were incorporated due to their taxonomic association with efficacious exotic allies. Statistical analyses of the weighting processes employed were not possible in the absence of screening results which are due only in December 2006. The legislation governing bioprospecting in South Africa is discussed and several recommendations are presented to minimise negative impacts on the industry.
Cape elements on high-altitude corridors and edaphic islands.
(2004) Carbutt, Clinton.; Beckett, Richard Peter.; Edwards, Trevor John.
Common to the temperate floras throughout sub-Saharan Africa is a group of taxa with strong ties to the Cape Floristic Region (CFR) (≈ Cape elements). Their distribution is limited to the eastern escarpment of Africa (e.g. the Drakensberg Alpine Centre - DAC), on nutrient-rich humic soils, as well as on isolated sandstone outcrops of low elevation, on nutrient-poor soils (e.g. the Pondoland Centre - PC), suggesting that intrinsic soil fertility is not the primary determinant of their distribution. The principal aim of this study was to determine which aspect of the edaphic environment of the DAC is most influenced by temperature, that may indirectly render it nutrient-poor and therefore provide suitable niches for Cape elements, as in the PC. A multidisciplinary approach involving aspects of plant biogeography, plant ecology, plant ecophysiology and soil chemistry was therefore adopted. The study regions were the DAC, PC and the KwaZulu-Natal Midlands. The flora of the DAC was resurveyed for this study, and is richer than previously thought: 2818 native taxa, most of which (2520) are angiosperms. The phytogeography of the DAC and PC is discussed, and comparisons are made with the floras of KwaZulu-Natal and the CFR. Their climatic environments, as well as those for the CFR and Sneeuberge, were compared using rainfall and temperature data from a range of sources. These climatic regimes were correlated with the floristic patterns of Cape elements for the high-altitude regions of South Africa and Lesotho. Altitude and rainfall increased, and temperature decreased, as the number of Cape elements increased towards the DAC. This study provided a contemporary inventory of the Cape elements of the DAC and PC. A total of 89 genera are recognised as Cape elements, of which 60 (c. 67%) are shared between the two regions. The highest number of Cape elements recorded for the eastern escarpment was the DAC (72 genera), with the highest number from all sites analysed being the PC (77 genera). The most Cape elements are contributed by the Asteraceae, Scrophulariaceae, Iridaceae, Fabaceae, Orchidaceae and Restionaceae, partly due to the success of annual aerial parts and their geophytic growth forms, which are convergent in these families. Further compartmentalisation into life and growth forms shows that most Cape elements of the DAC and PC are either ericoid (and sclerophyllous) or mesic herbs and shrubs. The ecological and ecophysiological aspects of this study involved the use of reciprocal pot experiments established along a gradient of altitude from coastal hinterland to mountain, that investigated the interactions between altitude, temperature and substrate on plant productivity in sites known either to support or to exclude Cape elements. Three soils were used at each site, representative of the DAC, PC and KwaZulu-Natal Midlands. The interactions between 'soil' and 'site' (≈ the climatic environment) were quantified using a temperate test taxon (Diascia) that has a strong Cape-centred distribution. Plant characters relating to morphology and nutrient content, and soil characters relating to fertility, were used as the basis for comparing treatment effects (soil-site interactions). Soil nitrogen availability was assayed using pot experiments with Eragrostis curvula (Schrad.) Nees. Wheat pot experiments revealed no Al³⁺ toxicity in 'Drakensberg' soil. Non-metric multidimensional scaling (NMDS) and redundancy analysis (RDA) indicated that all soil-site interactions were significant contributors to biomass differences, and that the Cape taxon performed poorly in the nutrient-rich Drakensberg soil at low altitude. Soil samples indicated that Drakensberg soil was the most nutrient-rich, and Pondoland soil the most nutrient-poor. Although total nitrogen in Drakensberg soil was six times higher than Pondoland soil, both soils mineralised similar low levels of nitrogen at their respective spring temperatures. The result for Drakensberg soil (simulated so as to include the effect of altitude) meant that only 1.7% of its total nitrogen was mineralisable at 12°C (its mean spring temperature). These findings suggest that nitrogen mineralisation rate is a key growth-limiting factor in the DAC, exacerbated by a number of complex interactions with soil pH and organic matter. It is hypothesized that Cape elements are preadapted to high-altitude habitats. These habitats are nutrient-deprived due to low temperatures, which reduce metabolic rates and the movement of ions in cold soils. This constraint imposes nutrient-related stresses similar to those of the CFR and PC. Taxa that are adapted to the nutrient-poor soils of the CFR are preadapted to the temperature-induced 'nutrient-poor' soils of the DAC and vice versa. This 'compatibility' has allowed the reciprocal exchange of taxa between regions, as suggested by cladistic biogeographical analyses using Cliffortia, Disa, Moraea and Pterygodium. The strong overlap of Cape elements between the CFR and PC is a product of similar nutritional niches and ancient floristic continuity. The result therefore is a high number of Cape elements common to the DAC and PC.
Character variation and a cladistic analysis of the genus Lachenalia Jacq.f. ex Murray (Hyacinthaceae:Massonieae)
(2005) Duncan, Graham D.; Edwards, Trevor John.
Morphological variation and a cladistic analysis of the large, endemic Southern African genus Lachenalia Jacq.f. ex Murray (Hyacinthaceae: Massonieae) is presented. Its close taxonomic relationship with the small endemic sympatric genus Polyxena Kunth (which has been included in the morphological and cladistic study) is discussed. The inclusion of Polyxena within Lachenalia is supported. One hundred and twenty species (139 taxa), comprising 115 Lachenalia and five Polyxena species are recognised. A wide range of morphological characters were analysed, including macromorphology, micromorphology, anatomy and palynology. A discussion and comparison of karyological data is also presented. A brief historical background, species diversity maps, figures, tables, appendices and illustrations of anatomical, micromorphological and macromorphological characters, and cladistic data, are presented, as well as discussions of pollination biology and phytogeography. This work is based on species studied in their natural habitats as well as under cultivation, and from representative herbarium specimens examined from BOL, NBG, PRE and SAM.
Conservation of select South African Disa Berg. species (Orchidaceae) through in vitro seed germination.
(2003) Thompson, David Ian.; Edwards, Trevor John.; Van Staden, Johannes.
Disa comprises 163 species, 131 of which occur in South Africa (SA). The genus is distributed across winter- and summer-rainfall areas, but few species transverse both climatic regions. Species are therefore regarded as winter-rainfall or summer-rainfall endemics - yet release their seeds in autumn, irrespective of provenance. Disa contributes 40 % of threatened Orchidaceae in SA, with half of the local species requiring conservation initiatives. In vitro seed germination is a potential conservation tool for producing large numbers of genetically diverse plants in relatively short periods. However, only 11 winter-rainfall Disa species are easily germinated ex situ. Studies were therefore undertaken on summer-rainfall taxa, which are ungerminated in vitro, in an effort to define their germination parameters. This thesis describes mechanisms that control germination in Disa and establishes practical propagation methods for seed culture. Two seed types occur in Disa; i) comparatively large, pale and pyriform seeds in members of the D. uniflora sub-c1ade, which populate streamside habitats under conditions of winter-rainfall maxima, and ii) smaller, variously brown and fusiform seeds in the remainder of the genus. Seed morphometrics distinguished seed types, although embryo dimensions were similar. Testa continuity, which is disrupted in the large seeds, also supported separation. Typically, small seeds are ungerminated in vitro, whilst large seeds germinated readily. Increased seed size did not necessarily impart increased germ inability, as several germinable, small-seeded species exist - being winter-rainfall species Attempts to establish in vitro germinability revealed that increased water availability and charcoal supplementation promoted germination in intractable species. The control of germination was therefore proposed as a trade-off between water availability and the presence of phyto-inhibitors - two features typical of seeds exhibiting water-impermeable dormancy. Three germinability categories were recognized; i) easily germinable species, ii) poorly germinable species through media manipulation, and iii) ungerminated species. Germination of immature seed in the absence of media modification was comparable to mature seed germination under modified conditions, providing evidence of the role of an impermeable seed testa in regulating germination. Testa impermeability in mature, small-seeded species was demonstrated using aqueous EVANS' blue dye and was linked to i) testa integrity and ii) increased levels of leachable phenolics (LPC) - which are hydrophobic and phytotoxic. In addition, this research revealed an impervious and elaborate embryo carapace in small seeds. Large-seeded species were highly permeable at dehiscence, with perforated testae and negligible LPC. Germinability was ultimately defined by a significant regression with LPC. Phenolic deposition increased exponentially with increasing seed maturity and reflected decreased permeability and the development of testa colouration. The testa precludes the use of viability stains such as nc and FDA, unless rendered permeable through scarification. This was achieved using NaOCI. Viability and germinability percentages did not correlate well for the small-seeded Disa species, indicating that i) the methods used to break dormancy are inadequate, ii) additional factors may be acting in concert with the testa to regulate germination and iii) that the determination of mature Disa seed viability is ineffective. As an alternative, the germination potential of immature seed was estimated as the ratio between the proportion of embryos stained with TTC and the proportion of seeds permeable to EVANS' blue. Attempts to relieve water-impermeable dormancy in Disa resulted in the formulation of a dual-phase protocol - with the specific aim of increasing water availability to the embryo. Dual-phase cultures comprised a solid, charcoal-rich medium overlaid with a reduced strength, liquid medium fraction of the same type. The solid fraction negated the influence of leached phenols and allowed protocorms to establish polarity, whilst the fluid fraction increased water availability. The dual-phase protocol allowed germination of nine summer-rainfall Disa species, usually in percentages that approximated their estimated germination potential. For the remaining species, germination is controlled by more complex factors. Large seeds are atypical in containing starch, the hydrolysis of which facilitated their rapid, autonomous germination. Small-seeded Disa species stored lipids and proteins and germinable species accumulated starch post-germination. The embryo protoplasts of all species contained appreciable amounts of soluble sugars, irrespective of germinability. However, decreased sucrose and increased fructose correlated significantly with decreased seed germinability. This study provides evidence of the nutritional value of mycotrophy, with endophytes liberating soluble carbohydrate and non-carbohydrate compounds upon lysis. However, few species were germinated symbiotically, suggesting that endophytes isolated from adult roots do not necessarily support germination in the same species. Similar endophytic fungi occur in Australian and Holarctic orchids.
Pollination of Plectranthus L'Her. (Lamiaceae) along the Eastern seaboard of southern Africa.
(2009) Potgieter, Christina Johanna.; Edwards, Trevor John.; Van Staden, Johannes.
Pollination data is provided for a third of the Plectranthus species in southern Africa. In the largest genus of Lamiaceae in the region (53 species), 18 were studied, plus two species of allied genera (Pycnostachys urticifolia and Aeollanthus parvifolius). Study of these 20 species aimed to describe the groups of pollinators that have driven pollinator specialisation. Case histories are provided upon which future studies of Lamiaceae pollination, breeding systems and speciation may be based. Bees (Apidae) and flies (Nemestrinidae, Acroceridae and Tabanidae) are the main pollinating insect groups. Seven straight-tubed Plectranthus species show a match between corolla tube- and proboscis length of nectar-feeding pollinators. Long-proboscid nemestrinid flies are specialised on long-tubed Plectranthus species (P. ambiguus, P. hilliardiae, P. reflexus and P. saccatus), while shorter-proboscid flies of all three families are important pollinators of straight-tubed species with medium- and short corolla tubes. Seven species with sigmoid corolla tubes are bee-pollinated, with fly-pollination prevalent in some. Bent corolla tubes, coupled with length, act as barriers to illegitimate nectarfeeders and ensures alignment of pollinators for effective pollen placement and carryover. It is suggested that straight-tubed species may have evolved from sigmoid-tubed species. Long-tubed species with straight corollas in other Lamiaceae may show convergent pollination by long-proboscid flies, with the guild being dependent on habitat and distribution of plants and flies. Formal establishment of the Stenobasipteron wiedemanni pollination guild extends the study from Plectranthus to selected Acanthaceae, Orchidaceae, Balsaminaceae, Gesneriaceae and Iridaceae, occurring in forested habitat along the Eastern seaboard. Micro-distillation of essential oils confirmed parentage of a putative natural hybrid; once established, hybrid data allows studies of the importance of natural hybridisation events in explaining pollinator fidelity. Nectar sugar studies in Plectranthus mostly showed sucrose dominance; cases of hexose dominance are noted and discussed. Nectar volume and concentration proved variable and do not fit any trends. Pollination by medium-proboscid acrocerid flies has importance for ‘medium-tubed’ plants, since six of the Plectranthus species are solely or partially reliant on Acroceridae for pollination. An appendix with consolidated data describes the 20 study species i.t.o. morphology, habitat, study sites, field work, pollinator observations and insect vouchers.
The reproductive biology, natural enemies and biological control of Delairea odorata Lem.
(2000) Rolando, Carol Ann.; Edwards, Trevor John.
Delairea odorata Lem., an asteraceous perennial vine indigenous to southern Africa, has become naturalised and invasive in many subtropical regions including California, South Australia and Hawaii. Biological control offers a potential long term solution to the management of this species in exotic locations. This study analysed aspects of the biology of D. odorata in its native environment to determine its suitability to classical biological control. To this end an examination of the reproductive biology and natural enemies of D. odorata was made. A study of the pyrrolizidine alkaloid profile was also conducted. Reproductive biology: Delairea odorata reproduces both sexually by seeds and asexually by stolons. The flowering season occurs over the autumn months from April to June. Results of the pollination trials indicate that D. odorata is a cross compatible species and an obligate outbreeder. There is no specialised pollination system and the predominant pollinators belong to the families Apidae, Syrphidae and Calliphoridae. Following pollination, numerous small achenes are produced. Laboratory trials indicate that these achenes germinate readily between 10 and 25 °C and, although germination occurs in both the light and dark, light clearly stimulates seed germination. Greenhouse trials conducted to determine the effect of light on growth and reproduction indicate that D. odorata is a shade tolerant species which shows plasticity in terms of growth form and deployment of biomass in response to changes in light intensity. Growth rate and allocation of biomass to vegetative and sexual reproduction are highest at an intermediate light level. However, greatest allocation of biomass is to stem growth regardless of light level. Natural enemies: Surveys for potential biological control agents against Delairea odorata were conducted in KwaZulu-Natal and several phytophagous species were associated with the plant. However, only one potentially suitable control agent was identified, a stem galling tephritid fly, Parafreutreta regalis Munro. Preliminary studies indicate this species to be fairly host-specific, a valuable asset if it is to be considered as a control agent. Furthermore, as D. odorata proliferates extensively by means of stem regeneration and elongation, galling of these growing points by P. regalis may limit stolon spread in exotic locations. Two species of parasitic wasp (Braconidae) were found to parasitise P. regalis pupae. If P. regalis is to be used as a control agent the likelihood of parasitisation in the new environment must be determined. Pyrrolizidine alkaloids: Host-specificity in insects is often dependent on host-plant chemistry (e.g. alkaloids or essential oils). Thus prior to any biological control programme it is important to determine if there are ecotypes of the host plant present. An investigation to determine the specificity of the pyrrolizidine alkaloid profile of D. odorata, occurring across KwaZulu-Natal, was made. The results indicate the presence of nine retronecine based pyrrolizidine alkaloids which occur in similar proportions in locally distributed plants. However, these alkaloid profiles differ considerably from those published for D. odorata occurring in California. This is an interesting and important result which indicates that chemotypes of D. odorata may exist, a factor which must be considered in the initiation of any biocontrol. If chemotypes of D. odorata are present this may affect the behaviour of natural control agents on the exotic plant populations.
A revision of Argyrolobium (Crotalarieae, Fabaceae) in South Africa.
(1994) Edwards, Trevor John.; Van Staden, Johannes.; Stirton, C. H.
A revision of 45 South African species of Argyrolobium is presented comprising nomenclature, typification, recorded distributions and full descriptions. In an attempt to reduce confusion between subtly different species, diagnostic characters are listed and comprehensive illustrations are provided. The dissertation includes numerous taxonomic and nomenclatural changes. Currently two sections are recognised based on fruit morphology. This is replaced by a system of five new sections based on morphological, micromorphological and phytogeographical evidence. Constraints and advantages of floral dimorphism and monomorphism are discussed with respect to the fecundity and distribution of sections. It is proposed that the occurrence of facultative cleistogamy in two sections has enhanced their success and distribution. Generic and specific phylogeny is interpreted using models generated through cladistic methodology.
A revision of the genus Ledebouria Roth (Hyacinthaceae) in South Africa.
(1993) Venter, Stephanus.; Edwards, Trevor John.
Members of the genus Ledebouria Roth (Hyacinthaceae), which occur in South Africa, are revised. This genus occurs throughout Africa, India and Madagascar. 33 Species are recognized and placed into nine provisional infrageneric groups. A multidisciplinary approach was used in an attempt to provide natural groupings. The following characters were analysed; morphology, micromorphology, palynology and caryology. Aspects of ovary structure and leaf micromorphology proved especially useful in the synthesis of infrageneric and specific concepts. Keys, descriptions, illustrations, distributional, ecological, medicinal and toxicological data are provided. This study is based on plants in their natural habitat, cultivated specimens and representative herbarium specimens from herbaria in South Africa and in Europe.
A synfloristic comparison of Oribi Gorge and Umtamvuna Nature Reserves.
(1998) Meter, Edna Beatrice.; Edwards, Trevor John.
Climatic oscillation during the Quaternary resulted in fragmentation of once more continuous ancient floras and a series of invasions of different floras into the Pondoland Centre in response to climatic change, with some elements invading more than once. This implies both a temporally complex and a floristically complex origin for the extant flora of the Centre. Data derived from analysis of the melange of extant floristic elements in the Pondoland Centre is presented in support of this hypothesis. A synfloristic comparison of Oribi Gorge (OGNR) and Umtamvuna Nature Reserves (UNR) is the basis for this study. A comparison of the species lists generated for OGNR and UNR reveals that 24% of the 1514 angiosperm species are shared. The familial composition of the reserves is similar, with eight of the ten most diverse families contributing a similar proportion of species to the respective floras, with the exception of Acanthaceae. The ten most diverse families comprise a comparatively small proportion of the respective floras; this is indicative of high diversity over long geological periods, i.e. of refugia. Analysis at the generic level revealed similar consistancy between the two gorge floras. Approximately 4% of the UNR species and 2.3% of OGNR species are Pondoland Centre endemics. Approximately 40% of the endemic species are shared by the gorges. Data reveals that both palaeoendemic (predominantly woody, forest taxa) and neoendemic (predominantly herbaceous or suffrutescent, grassland taxa) species occur. The Pondoland Centre is thus a refugium for species trapped on the Msikaba Group sandstones as a result of climatic oscillation during the Quaternary, and a centre of neoendemism. OGNR and UNR floras include Cape, Afromontane and tropical elements (11.3%, 2.8% and 19.1% respectively for OGNR and 16%,3.4% and 15.3% respectively for UNR). Seventy - two percent of Afromontane species are shared, indicating a relatively recent invasion(s) and lor the relative proximity of the gorges to the Afromontane flora. The lower species overlap in the Cape element (39.2%) of the two gorges implies that the invasion of the element is ancient, with subsequent extinction of many of the taxa from OGNR in response to climatic change. It is also possible that this invasion was initally less successful; fewer species found refuge in OGNR. The tropical element comprises the largest proportion of the flora in both gorges and many (ca. 50%) of the species are shared. The degree of species overlap indicates that the invasive flora was either initially more similar or that it is tess prone to extinction. The level of overlap could also suggest that the invasion was more recent than that of the Cape taxa. The tropical element is larger in OGNR and the Cape element is larger in UNR. This is partly due to the gorges' respective proximities to the tropical and Cape floras. This trend is echoed in the endemic data. iv The conservation status of the endemics and of the Pondoland vegetation types is established and recommendations for further research are made. The data support the establishment of a larger UNR, the maintenance of both Umtamvuna and Oribi Gorge as formal nature reserves and the establishment of a new reserve (or reserves) within the Pondoland Centre.
Systematic studies in Gnidia L. (Thymelaeaceae)
(2010) Beaumont, Angela Jane.; Edwards, Trevor John.; Van Staden, Johannes.
Gnidia L., variously estimated to contain 100–160 species, is the largest genus in the sub-cosmopolitan family Thymelaeaceae. Most species are shrubby, and occur in tropical and southern Africa, with one species reaching southern India and Sri Lanka, and 14 species endemic to Madagascar. Assorted segregate genera have been established using characters considered by some as too few, too trivial or unreliable. Generic limits have been contentious with authors following either a narrower concept of Gnidia or a broader circumscription within which segregate genera are placed in synonymy under Gnidia. Regional treatments for African and Madagascan floras have been published over the last century until very recently, but the genus was last revised in its entirety 153 years ago. Today, a broad-based concept of Gnidia is generally recognised, but there is no modern infrageneric classification, and species relationships are poorly understood. Homogenous groups of species are identified by their similarities of leaf length and width or bract length and width ratios. Species comprising the homogenous groups for leaf ratios differ to those comprising the homogenous groups based on bract ratios, and there is no correlation between leaf and bract length and width ratios. This suggests that the factors influencing leaf diversity differ from those influencing bract diversity. Bracts differ most from leaves in species with capitate inflorescences, and involucres of several layers of bracts likely protect reproductive organs (flowers) in heads. Previously overlooked morphological and micromorphological details, and morphometric analyses of leaf, bract and floral dimension data help define individual species, and clades of species derived from phylogenetic analyses of molecular data. Evidence from a phylogenetic analysis of nuclear ribosomal and plastid DNA sequence data confirms the polyphyly of Gnidia. Three lineages contain Gnidia species and species of genera from southern Africa, southern South America or Australia, while another lineage corresponds largely to the previously recognized genus Lasiosiphon. The genus Lasiosiphon is reinstated characterised by flowers mostly in heads, bracts different from the leaves, and the presence of smooth hairs; it now includes species with tetramerous flowers as well as ones with pentamerous flowers. Gynodioecy is recorded for the first time in a single species and represents the first documented example of sexual polymorphism involving unisexual flowers in Gnidia and sub- Saharan Thymelaeaceae. The findings of this thesis are discussed in terms of their phylogenetic value and contribution to our better understanding of the generic limits of Gnidia and its relationships with other southern hemisphere Thymelaeoideae. The circumscription and generic affinities of Gnidia as suggested by results presented in this thesis are compared to previous classification systems for congruence and dissimilarity.
A systematic study of Leonotis (Pers.) R. Br. (Lamiaceae) in southern Africa.
(1995) Vos, Wayne Thomas.; Edwards, Trevor John.; Van Staden, Johannes.; Smith, Michael Trevor.
The southern African species of Leonotis (Pers.) R. Br. are revised. Nine taxa are recognised including a new species and two new subspecies. A multidisciplinary approach was adopted involving: floral, vegetative, seedling and fruit morphology, karyology, palynology, pollination biology, phytogeography, phytochemistry and cladistics. Of these characters the most important in delimiting species is leaf morphology. Phytochemistry revealed qualitative and quantitative differences in essential oils between taxa. Germacrene is the dominant essential oil in seven species, particularly in L. dubia E. Mey. and L. nepetifolia (L.) R. Br. Caryophyllene dominates in L. randii S. Moore. Although certain species have characteristic aromas, no inter-specific differences are apparent in the levels of α-copaene, the dominant volatile essential oil extracted with Tenax. Essential oil data is in partial agreement with the phylogeny and species concepts presented in this document. Omithophily accounts for most fruit set in perennial species but in the annual species (L. nepetifolia) autogamy prevails. Neither omithophily nor entomophily improved nutlet vigour which was gauged from nutlet germination. Leonotis species are predominantly pollinated by a variety of sunbirds, although bees are also involved. Nectar is sucrose-dominant in perennial species but hexose-dominant in the annual. The majority of species are concentrated along the eastern seaboard with the eastern Cape forming the centre of diversity. The widespread distribution and tropical affinities of L. leonurus (L.) R. Br., suggest an origin for the genus in tropical Africa. Migration to southern Africa and subsequent speciation are suggested. Habitat diversity and edaphic conditions probably played an important role in the evolution of narrowly distributed xerophytic species. A cladistic analysis re-emphasised that Leonotis is a monophyletic group of closely related species. The lack of floral divergence in perennial species indicates the constraints imposed by ornithophily. The annual, L. nepetifolia, is highly derived and displays numerous autapomorphies. The morphology, distribution and tropical affinities of L. leonurus are interpreted as pleisiomorphic. The proposed phylogeny is reasonably compatible with phytogeographic data.