Are plant taxa found on the Witwatersrand serpentine ecotypes or substrate-generalists?

Abstract

Serpentine soils vary in levels of toxicity of the parent material, climate, relief, and biological activity resulting in a range of harsh environments. This harsh environment is likely to result in a unique, usually endemic, flora. However, not all plants growing on serpentine soils are endemic; some plants appear to be indifferent (bodenvag) to the serpentine condition. It is likely that these apparently bodenvag serpentine taxa may be ecotypically differentiated into serpentine tolerant and intolerant races whilst appearing morphologically indistinguishable (cryptic). This study investigated whether aspects of life history (biomass, productivity, life forms) and breeding system characteristics (pollen viability, pollen/ovule ratios, pollinator exclusions, pollination syndromes) could indicate ecotype formation in selected, apparently bodenvag, serpentine taxa on the Witwatersrand. Multivariate analyses, namely correspondence analysis (CA) and principal component analysis (PCA) as well as Student's . t-tests, were used to analyse the data. The results indicate that reproductive and life history data do not separate the study taxa into ecotypes. This study concludes that the relatively mild serpentine condition on the Witwatersrand does not exert a strong influence on plants and that there is still likely to be gene flow amongst the study taxa growing on and off serpentine soils. © 2012 South African Association of Botanists.