Browsing by Author "Linder, H Peter"

Now showing 1 - 12 of 12
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    A comparative study of Grewia bicolor Juss. and Grewia flava DC
    (2000) Bartsch, Silke; Linder, H Peter
    Grewia bicolor and Gewia flava have been recognized by earlier authors as separate species on the basis of the shape of the leaf base, the number of flower stalks on the peduncle and reticulate venation of the tertiary veins. These two "species" are extremely variable, and often characters from G. bicolor and G. flava are exhibited on the same specimen. This study aims at evaluating the distinction between the two "species", thereby testing whether they should be recognized as separate taxa, and if so, which characters can be used to delimit G. bicolor and G. flava. Numerical phenetic analyses of 11 characters investigated from 211 herbarium specimens revealed that the two "species" cannot be differentiated by the traditional characters. Univariate analysis showed that the diagnostic characters that have been used to date show continuous variation. Thus G. bicolor and G. flava cannot be recognized as separate species.
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    Consistent phenological shifts in the making of a biodiversity hotspot: the Cape flora
    (BioMed Central Ltd, 2011) Warren, Ben; Bakker, Freek; Bellstedt, Dirk; Bytebier, Benny; ClaSZen-Bockhoff, Regine; Dreyer, Leanne; Edwards, Dawn; Forest, Felix; Galley, Chloe; Hardy, Christopher; Linder, H Peter; Muasya, A Muthama; Mummenhoff, Klaus; Oberlander, Kenneth; Quint
    BACKGROUND: The best documented survival responses of organisms to past climate change on short (glacial-interglacial) timescales are distributional shifts. Despite ample evidence on such timescales for local adaptations of populations at specific sites, the long-term impacts of such changes on evolutionary significant units in response to past climatic change have been little documented. Here we use phylogenies to reconstruct changes in distribution and flowering ecology of the Cape flora - South Africa's biodiversity hotspot - through a period of past (Neogene and Quaternary) changes in the seasonality of rainfall over a timescale of several million years. RESULTS: Forty-three distributional and phenological shifts consistent with past climatic change occur across the flora, and a comparable number of clades underwent adaptive changes in their flowering phenology (9 clades; half of the clades investigated) as underwent distributional shifts (12 clades; two thirds of the clades investigated). Of extant Cape angiosperm species, 14-41% have been contributed by lineages that show distributional shifts consistent with past climate change, yet a similar proportion (14-55%) arose from lineages that shifted flowering phenology. CONCLUSIONS: Adaptive changes in ecology at the scale we uncover in the Cape and consistent with past climatic change have not been documented for other floras. Shifts in climate tolerance appear to have been more important in this flora than is currently appreciated, and lineages that underwent such shifts went on to contribute a high proportion of the flora's extant species diversity. That shifts in phenology, on an evolutionary timescale and on such a scale, have not yet been detected for other floras is likely a result of the method used; shifts in flowering phenology cannot be detected in the fossil record.
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    Evolution of floral morphology in Brunsvigia and Crossyne (Amaryllidaceae)
    (1998) Raimondo, Domitilla C; Linder, H Peter; Snijman, D A
    Floral morphology and its relationship to pollination syndromes is examined, for the genera Brunsvigia and Crossyne (Amaryllidaceae). These two genera have similar vegetative morphologies and share the same mode of seed dispersal (anemogeochory). They differ in their floral and inflorescence structures. The species Brunsvigia bosmaniae and Crossyne flava are chosen as representative species of the two genera Brunsvigia and Crossyne. Floral morphology is studied in relationship to an outgroup species Nerine humilis. Pollination syndrome, ability to self-pollinate, levels of natural seed set and patterns of seed dispersal are studied so that reproductive strategies pf the two species can be compared. Crossyne flava is pollinated by a suite of small diurnal insects and can be considered to have a generalist pollination syndrome. The first observation of pollination by moths in Brunsvigia bosmaniae is reported. I show that neither species is able to self, hence pollination events are important. Experimental manipulation reveals that Brunsvigia bosmaniae is pollinator limited. Although this experimental manipulation was not possible for Crossyne flava, high seed set levels in Crossyne flava suggests that levels of pollination are high in Crossyne and low for Brunsvigia. The amount of pollination that takes place is shown to be closely related to floral morphology. Floral divergence of the two genera is thus proposed to be the result of adaptation to a pollinator driven selective regime.
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    The functional, ecological and evolutionary significance of culm structures in the Cape Floristic Region
    (2011) Yates, Megan J; Cramer, Michael D; Verboom, G Anthony; Linder, H Peter
    The Cape Floristic Region lies in the southwestern Cape, South Africa, and is known for its high species richness and endemism. This Mediterranean-type climate region receives winter rainfall that averages between 250 and 650 mm annually over most of the region but reaches an average of more than 1000 mm in the mountains of the southwest and southern Cape.
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    A molecular phylogeny of the subfamily Arundinoideae (Poaceae)
    (1995) Barker, Nigel Paul; Linder, H Peter; Harley, Eric H
    The subfamily Arundinoideae has long been considered to be an unnatural assemblage of genera, the relationships of which are obscure or unknown. Because morphological and anatomical data have, to date, been unable to elucidate relationships among these genera, sequence data from two chloroplast genes are used to elucidate relationships among 33 arundinoid genera. Sequence data from the variable, grass-specific insert in the rpoC2 gene is used to determine the relationships among 73 grass species from all currently recognised subfamilies. Phylogenetic analysis of this sequence data required the development of specialised alignment techniques based on testing assumptions of positional homology. Results of the analyses based on these alignments suggest that the Arundinoideae is divisible into four lineages, corresponding approximately to the tribes Danthonieae, Arundineae, Aristideae and Thysanolaeneae. Several arundinoid representatives are placed in other subfamilies. The rpoC2 sequence data was too variable to elucidate relationships at the tribal and subfamilial level. For this purpose, sequence data of the highly conserved rbcL gene was obtained from 22 taxa selected from the lineages identified by the rpoC2 study. Phylogenetic analysis of a total of 36 sequences resolved some of the relationships of the major clades, but other relationships were poorly supported. In an attempt to improve the resolution of these major clades, the rpoC2 and rbcL data sets were combined with restriction site data. These three data sets were analysed in a variety of combinations using both data combination and tree consensus methods to assess support of the phylogenetic relationships. Despite this, the resolution of the relationships among the Arundineae, Danthonieae, Aristideae and Chloridoideae was not resolved with any finality, although a (Arundineae (Danthonieae (Aristideae, Chloridoideae))) relationship is proposed as being most likely. The molecular phylogeny implies that eight grass subfamilies should be recognised. Two of these, the Danthonioideae and Aristidoideae, are new and the Arundinoideae is redelimited. Furthermore, new tribes in the subfamilies Centothecoideae (Thysanolaeneae) and Chloridoideae (Centropodieae) are proposed to accommodate lineages and taxa misplaced in the subfamily Arudinoideae as previously delimited.
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    Optimising regionalisation techniques: identifying centres of endemism in the extraordinarily endemic-rich Cape Floristic Region
    (Public Library of Science, 2015) Bradshaw, Peter L; Colville, Jonathan F; Linder, H Peter
    We used a very large dataset (>40% of all species) from the endemic-rich Cape Floristic Region (CFR) to explore the impact of different weighting techniques, coefficients to calculate similarity among the cells, and clustering approaches on biogeographical regionalisation. The results were used to revise the biogeographical subdivision of the CFR. We show that weighted data (down-weighting widespread species), similarity calculated using Kulczinsky's second measure, and clustering using UPGMA resulted in the optimal classification. This maximized the number of endemic species, the number of centres recognized, and operational geographic units assigned to centres of endemism (CoEs). We developed a dendrogram branch order cut-off (BOC) method to locate the optimal cut-off points on the dendrogram to define candidate clusters. Kulczinsky's second measure dendrograms were combined using consensus, identifying areas of conflict which could be due to biotic element overlap or transitional areas. Post-clustering GIS manipulation substantially enhanced the endemic composition and geographic size of candidate CoEs. Although there was broad spatial congruence with previous phytogeographic studies, our techniques allowed for the recovery of additional phytogeographic detail not previously described for the CFR.
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    The phylogeny of Brachycorythis Lindl. and Neobolusia Schltr
    (1999) Chuba, David; Linder, H Peter
    The monophyly of the genus Brachycorythis has been tested. The phylogeny of the African genera of Orchidinae - Orchideae - Orchidaceae (Schwartzkopffia, Brachycorythis, Neobolusia, Schizochilus, Dracomonticola, Holothrix and Bartholina is estimated with special attention to phylogenetic positions of Brachycorythis and Neobolusia. Pollen surfaces of twelve of the species are examined. Thirty-eight morphological and anatomical characters for 25 species of the species mentioned above are cladistically analysed and the stability of the different clades of the most parsimonious trees determined using various clade stability indices. The current delimitation of the Southern African Orchidae genera, with Neobolusia and all the other genera being independent from Brachycorythis is supported. Pollen surface ornamentation also shows the only species of Neobolusia examined for this (N. tysonii) as being quite different from the rest of the genera studied in having intectate pollen whereas the rest have semitectate pollen. This has further indicated support for the independence of Neobolusia from the genus Brachycorythis.
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    Questioning the Cunonia in C. capensis
    (1995) Kruger, Lynette; Linder, H Peter
    All members of Cunonia, excluding C. capensis, occur on the island of New Caledonia. Dickison has repeatedly noted (1973, 1975, 1980, and 1984,) that evolutionary patterns may have led to incorrect systematic conclusions among many cunoniaceous genera, which are likely to generate incorrect systematic conclusions. For this reason, a study into the morphological characters defining C. capensis was undertaken. Although the possibility that the disjunct biogeographical pattern of C. capensis might be explained on the basis of taxonomic error was appealing, it was not conclusively supported from this investigation. Instead it was found that of the six characters supposed to distinguish Cunonia from Weinmannia, three agreed with the present position of C. capensis with Cunonia, whilst the other three placed C. capensis with Weinmannia. This study also served to highlight the need for further investigation and identification of characters which separate Cunonia and Weinmannia at the species level.
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    Species limits in the Rhodocoma gigantea (Kunth) Linder complex
    (1999) Mafa, Paseka; Linder, H Peter
    Rhodocoma gigantea and Rhodocoma foliosus have been recognised by earlier authors as separate species on the basis of perianth length and shape. Linder (1985) superficially lumped these two species under Rhodocoma gigantea arguing that the difference between the two appear to be brought by ecological gradient. Numerical phenetic analyses of 19 quantitative floral morphological characters investigated from 33 herbarium specimens reveal that Rhodocoma gigantea complex consists of two groups. One group corresponded to Rhodocoma gigantea, having longer and wider spikelets, perianth segments and bracts, while the other correspond to Rhodocoma foliosus having shorter and thinner female spikelets, bracts and perianth segments than the former. Minimum spanning tree also reveal the two groups are geographically isolated. The former group occur in the western part of the south coast along the Langeberg in Swellendam and Riversdale districts and the latter is widely distributed on the Outeniekwaberg, Tsitsikama mountains to Zuurberg with outliers reaching as far as Uitenhage. The Gouritz river appears to be the geographical barrier between these two species. The species boundaries of this complex are discussed and the two groups are suggested to be separated based on the phenetic species concepts.
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    The structure of the perennial growth of Disa uniflora Berg. (Orchidaceae)
    (1990) Thomas, Janet Clare; Linder, H Peter
    The perennation of orchids is poorly understood, in particular that of the Orchidoidae. The understanding of perennation in the Orchidoidae is important because the root-stem tuberoid is used as the one character defining the Orchidoidae as a monophyletic group. The root-stem tuberoid has never been examined for variation before. This project focuses on perennial growth in the Diseae in order to study the structure and function of the root stem tuberoid in relation to other organs and to contribute to the understanding of Orchidoid phylogeny.
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    A taxonomic study of the genus Lotononis (DC.) Eckl. & Zeyh. (Fabzceae, Crotalarieae)
    (1989) Van Wyk, Ben-Erik; Linder, H Peter
    The approach and methods used in a taxonomic study of the genus Lotononis (DC.) Eckl. & Zeyh. and related genera of the tribe Crotalarieae (Benth.) Hutch. are briefly introduced in Part 1. Morphological, cytological and chemical data was analyzed by cladistic methods to provide a sound basis for the generic delimitation of Lotononis and to formulate a natural infrageneric classification. The generic limits of Lotononis and its relationships with 14 other genera of the Crotalarieae are discussed in Part 2. Detailed morphological studies by Polhill (1976) has shown the widespread occurrence of convergence and conflicting character information in the tribe. Only a few of the genera are monothetic taxa and very few characters are available for cladistic analyses. This is not so much due to a lack of data but rather to ambiguity as to how morphological characters should be interpreted. It was therefore decided to concentrate on a study of alkaloids to test the predictivity of the present generic delimitations in the Crotalarieae. With the exception of Crotalaria L., virtually nothing was known about the alkaloids of the tribe (Mears & Mabry 1971, Kinghorn & Smolenski 1981). In the tribe Genisteae, alkaloid patterns show a high degree of conformity with evolutionary patterns based on morphological evidence (Polhill 1976) and the value of alkaloids as a generic character in the Leguminosae is well known (Kinghorn & Smolenski 1981). It seemed that more insight into generic relations in the Crotalarieae could be gained by concentrating on a hitherto much neglected field rather than to duplicate the detailed morphological studies of Polhill (1976). It was also clear that meaningful conclusions could be made about generic relationships, because the biogenetic pathways along which quinolizidine and pyrrolizidine alkaloids are formed are rather well known. The survey of major alkaloids (Appendices 1 to 11) indeed led to a much better understanding of the intricate relationships in the Crotalarieae, and made it possible to present a well supported and almost fully resolved cladogram for the tribe as a whole.
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    Variation in Thamnocortus insignis - genetically and environmentally plastic?
    (1999) Mgidi, Theresa Nobuhle; Linder, H Peter
    Environmental variation of Thamnocortus insignis Mast. (Restionaceae) is presented, by using average dry weight measurements of six populations of this species found along the coast of the Cape Province. The dry weight measurements were used to detect variation in the growth rates of the six populations, which in tum indicates the environmental variation among the populations. The results were showed no significant difference between all six populations and this was due to the relatively very small sizes of the seedlings when the measurements were taken. Genetic variation was investigated by using isozyme electrophoresis of the EST locus. One population (Puntjie) showed significant deviation from the Hardy-Weinberg equilibrium, whilst all the others agreed with the assumptions of the model except for the Superthatch-extra tall population, which was homologous. Estimation of allelic diversity among the populations produced a Fst of 0.098 that implies that there is a high level of gene flow among the six populations of the species. The allelic diversity estimate within populations was also very low (Fis = 0.079) implying that the genetic neighbourhoods are relatively large and there is a high incidence of gene flow within the populations. Both estimation results support the predicted results for dioecious wind-pollinated species such as T. insignis.