Premise of the study: The functional significance of leaf margins has long been debated. In this study we explore influences of climate, leaf lobing, woodiness, and shared evolutionary history on two leaf margin traits within the genus Pelargonium.

Methods: Leaves from 454 populations of Pelargonium (161 species) were collected in the Greater Cape Floristic Region and scored for tooth presence/absence and degree of lobing. Tooth density (number of teeth per interior perimeter distance) was measured for a subset of these. We compared five hypotheses to explain tooth presence and density using mixed effect models.

Key results: Tooth presence/absence was best predicted by the interaction of leaf lobing and mean annual temperature (MAT), but often in patterns opposite to the previous literature: species were more likely to be toothed with warmer temperatures. This was particularly the case for unlobed and highly lobed leaves. In contrast, tooth density was best predicted by the interaction of MAT and the season of most rain; density declines with temperature as consistent with expectations, but only in winter- rain dominated areas. Woody and non-woody species within Pelargonium both have similar associations between tooth presence/absence and MAT, contrary to the expectation that patterns within non-woody species would be insignificant.

Conclusions: We conclude Pelargonium leaf margins show predictable responses to climate, but these responses are complex and can contradict those found for global patterns across plant communities.

Please see https://github.com/henryf6/pelargonium_margins for code associated with these datasets.

See the README file.