Climate and leaf shape relationships in four Helichrysum species from the Eastern Mountain Region of South Africa

Morphological variation in plants can be affected by climate, which influences how species are identified as well as hypotheses of species divergence. We tested whether climatic niches were correlated with the observed morphological (leaf) variation of four geographically overlapping and reproductively similar Helichrysum species (Hilliard’s Group 4 in the southern African flora). We found that two species, H. gymnocomum and H. odoratissimum, showed clear evidence for climatic niche conservatism and that across all species leaf shape was not significantly correlated with climatic niche. Interestingly, there did appear to be a pattern, albeit statistically non-significant, that linked cold, dry climates to leaf shape, particularly for the variable and widespread H. odoratissimum. For example, smaller, narrower leaf shapes were generally found in cooler, drier regions, while large, broad leaves (particularly those of H. odoratissimum) are found in warmer, more humid regions. In addition, the data also showed that two species, H. odoratissimum and H. gymnocomum, comprised a single variable group. The climate-leaf shape patterns could potentially reflect the morphological variation between these two species. Collectively, these findings suggest further work is necessary to determine the role of climate and leaf shape variation in species divergence in the Eastern Mountain Region.