LEAF SHAPE EVOLUTION IN THE SOUTH AFRICAN GENUSPELARGONIUML’ HÉR. (GERANIACEAE)

Abstract

Leaf shapes reflect complex assemblages of shape-determining elements, yet evolutionary studies tend to treat leaf shape as a single attribute, for example cordate or linear. As with all complex structures, individual elements of a leaf could theoretically evolve independently and at different rates to the extent permitted by genetic and functional limitations. We examined relative evolutionary lability of shape-determining elements in the highly diverse South African plant genus Pelargonium (Geraniaceae).We used SIMMAP to calculate Bayesian posterior probabilities for ancestral states of leaf-shape characters for major nodes across multiple phylogenetic trees. Trees were derived from a Bayesian analysis of DNA sequence data from four partitions. We found that shape elements differed in rates of character-state transformations across the tree. Leaf base, apex, and overall outline had low rates. Transformations in venation occurred at slightly higher rates and were associated with shifts in venation among major clades. Leaf margin type and overall leaf size showed intermediate rates, whereas high rates were observed in the extent of lamina lobing and functional leaf size. The results indicate that suites of elements characteristic of the recently evolved xerophytic lineage, for example pinnate venation, dissected lamina, and entire margins, were acquired piecemeal over nested levels of the phylogeny. K E Y W O R D S :Ancestral character-state reconstruction, functional leaf size, leaf venation, leaf evolution, xerophytic plants.

The evolution and functional significance of leaf shape in the angiosperms

“…1), often within growth forms and taxonomic sections. Parsing of leaf form categorically revealed that the extent of dissection of the blade is highly evolvable within an overall ovate leaf shape outline that is evolutionarily conserved (Jones et al 2009). …”

Evolution of leaf form correlates with tropical–temperate transitions in Viburnum (Adoxaceae)

“…Leaf boundary layer models predict leaf shape as a key element of plant thermoregulation (reviewed in Nicotra et al [16]), but leaf shape has largely been neglected in global leaf-climate analyses (but see [8,17]). Jones et al [18] recently provided the first explicitly phylogenetic analysis of leaf shape evolution, in South African Pelargonium. They found that leaf size and degree of dissection were evolutionary labile traits, but surprisingly, the overall outline of the leaf was fairly conserved.…”

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

“…Selection pressures from climate variation across a geographic range could lead to locally adapted populations (Linhart and Grant 1996), which could result in significant morphological diversification of a taxonomic group in an ecologically diverse region (e.g., Jones et al 2009;Mitchell et al 2015). Therefore, investigating whether climate is linked to plant morphological diversity could provide insight into the drivers of leaf variation among related plant species and possibly species divergence.…”

“…Elements of leaf shape have been shown to be evolutionarily labile in ecologically diverse regions like the Cape Floristic Region (Jones et al 2009). Interestingly, environmental associations explained trait variation in closely related Protea species in South Africa, highlighting the potential role of evolutionary history in trait variation (Prunier et al 2012).…”