Showing papers by "University of Port Elizabeth published in 2006"

An overview of the Cape geophytes

Abstract: The Cape Region (here treated as the winter rainfall region of southern Africa, thus including fynbos, renosterveld and succulent karoo vegetation) is the world's foremost centre of geophyte diversity. Some 2100 species in 20 families have been recorded from this area, 84% of them endemic. The most important families, with more than a hundred geophyte species each, are Iridaceae, Oxalidaceae, Hyacinthaceae, Orchidaceae, Amaryllidaceae and Asphodelaceae. Although southern Africa does not appear to have been the main diversification centre for the plant orders with highest geophyte representation (Asparagales and Liliales), it represents an active centre of transition to geophytism, such transitions having occurred independently in numerous plant groups, often followed by rapid speciation. Several Cape geophyte groups have consequently expanded across Africa to the Mediterranean Basin, and possibly to other winter rainfall regions. Remarkably high local species diversity in renosterveld vegetation, even in relatively homogeneous environments, suggests that pollinator specificity and phenology play an important role in niche partitioning. However, character diversity is also high in storage organs and leaves, and this could account for the high species diversity values recorded at larger spatial scales, especially across environmental gradients. Long-term climatic stability, combined with topoclimatic and edaphic diversity and regular fire occurrence, is likely to be responsible for the remarkable geophyte diversity of the Cape, as compared to other mediterranean-climate regions. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 27–43.

Petal movement in cape wildflowers protects pollen from exposure to moisture

Abstract: We investigated diurnal patterns of petal movement (upright and reflexed) and sensitivity of pollen to moisture in a winter-flowering flora from the desert coast of Namaqualand, South Africa. Specifically, we tested the hypothesis that nocturnal flower closure associated with upright petal movement affords protection to pollen from winter precipitation. The proportion of open flowers in eight species from seven genera and three families, increased rapidly above air temperatures of about 20 °C. Flower temperature explained most of the variance in petal status. About 90% of the variance in flower temperature was explained by air temperature while radiation, wind speed and relative humidity had no significant independent effect. Petal opening was more closely correlated with temperature than the closing response, which may be under the additional control of endogenous factors. Pollen exposed to moisture overnight had a significantly higher frequency of damaged grains than control pollen in the majority of study species within the Aizoaceae and Neuradeceae. We found no evidence that pollen of asteraceous species exhibiting flower closure is sensitive to moisture. We conclude that pollen damage and the reduction in male fitness that may result from exposure to rain, dew and fog has provided an important selective impetus for the widespread evolution of upright petal movement and associated flower closure found among more than 3500 species in the predominantly winter and spring flowering Cape fynbos and succulent karoo floras.

Synthesis and characterization of rhenium(III) and (V) pyridylimidazole complexes

Abstract: Reaction of trans-[ReOCl3(PPh3)2] with 2-(2′-pyridyl)imidazole (pimH) in methanol led to the isolation of the rhenium(III) salt [ReCl2(pimH)(PPh3)2](ReO4) (1). However, with 2-(2′-pyridyl)-1-methylimidazole (pimMe) as ligand, the complex [ReCl3(pimMe)(PPh3)] (2) was obtained. The monooxorhenium(V) complexes [ReOCl3(pimR)] (R = H, Me) could only be prepared by the reduction of [ReO4]− with an equimolar amount of PPh3 in the presence of pimR and hydrochloric acid in acetic acid. With four equivalents of PPh3, compounds 1 and 2 were obtained. Using (n-Bu4N)[ReOCl4] as starting material, the μ-oxo dimers [Re2O3(pimR)2Cl4] were isolated as the only products. These new compounds have been characterized by X-ray crystallography, 1H NMR and IR spectroscopy. In 1 the [ReO4]− counterion is tightly associated with the cationic complex through N–H ··· hydrogen bonding. Despite being paramagnetic, 1H NMR spectra for 1 and 2 could be fully assigned.

Inclusion Compounds from a Host Mixture: A Cautionary Tale

Abstract: The inclusion properties of a dibenzocycloheptenol host with a variety of volatile guests have been analysed. The packing and intermolecular interactions of the inclusion compounds have been examined. Unexpected structures arising from impurities in the host, termed the ‘host mixture’, have been elucidated.

Lattices of Radicals of Ω-Groups

Abstract: Snider initiated the study of lattices of the class of radicals, in the sense of Kurosh and Amitsur, of associative rings. Various authors continued the investigation in more general universal classes. Recently, Fernandez-Alonso et al. studied the lattice of all preradicals in R-Mod. Our definition of a preradical is weaker than theirs. In this paper, we consider the lattices of ideal maps 𝕀, preradical maps ℙ, Hoehnke radical maps ℍ and Plotkin radical maps 𝔹 in any universal class of Ω-groups (of the same type). We show that 𝕀 is a complete and modular lattice which contains atoms. In general, 𝕀 is not atomic. 𝕀 contains ℙ as a complete and atomic sublattice, whereas ℍ and 𝔹 are not sublattices of 𝕀. In its own right, ℍ is a complete and atomic lattice and 𝔹 is a complete lattice. We identify subclasses of 𝕀, ℙ and ℍ that are sublattices or preserve the meet (or join) of these respective lattices.