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PremiseThere is considerable variation in leaf lobing and leaf size, including among grapevines, some of the most well-studied leaves. We examined the relationship between leaf lobing and leaf size across grapevine populations which varied in extent of leaf lobing.MethodsWe used homologous landmarking techniques to measure 2,632 leaves across two years in 476 unique, genetically distinct grapevines from 5 biparental crosses which vary primarily in the extent of lobing. We determined to what extent leaf area could explain variation in lobing, vein length, and vein to blade ratio.ResultsAlthough lobing was the primary source of variation in shape across the leaves we measured, leaf area varied only slightly as a function of lobing. Rather, leaf area increases as a function of total major vein length, total branching vein length, and decreases as a function of vein to blade ratio. These relationships are stronger for more highly lobed leaves, with the residuals for each model differing as a function of distal lobing.ConclusionsFor a given leaf area, more highly lobed leaves have longer veins and higher vein to blade ratios, allowing them to maintain similar leaf areas despite increased lobing. These findings show how more highly lobed leaves may compensate for what would otherwise result in a reduced leaf area, allowing for increased photosynthetic capacity through similar leaf size.

Geographical distribution and diversity of current plant species have been strongly shaped by climatic oscillations during the Quaternary. Analysing the resulting divergence among species and differentiation within species is crucial to understand the evolution of taxa like the Vitis genus, which provides very useful genetic resources for grapevine improvement and might reveal original recolonization patterns due to growth habit and dispersal mode. Here, we studied the genetic structure in natural populations of three species from eastern North America: Vitis aestivalis, V. cinerea and V. riparia using different marker types. Vitis aestivalis and V. cinerea showed higher diversity than V. riparia. The two former species are less differentiated, confirming an earlier divergence of V. riparia. V. aestivalis and V. riparia exhibited different genetic groups on both sides of the Appalachian Mountains that could mirror different recolonization routes from southern refugia. Genetic structure was stronger in V. cinerea, for which two varieties (var. berlandieri and var. cinerea) are morphologically recognized. Our results confirm this distinction and suggest the existence of three other lineages within var. cinerea. These discontinuities appear linked to adaptation of var. berlandieri to dry and limy areas of Texas and partially to the Mississippi River Valley. Rapid range expansions from refugia upon climate warming are also suggested by the low linkage disequilibrium values observed. Furthermore, large variation for downy mildew resistance was observed in the three species. Our findings appeared consistent with the vegetation history of eastern North America.