Premise The size and shape (physiognomy) of woody, dicotyledonous angiosperm leaves are correlated with climate. These relationships are the basis for multiple paleoclimate proxies. Here we test whether Vitis exhibits phenotypic plasticity and whether physiognomy varies along the vine. Methods We used Digital Leaf Physiognomy (DiLP) to measure leaf characters of four Vitis species from the USDA Germplasm Repository (Geneva, New York) from the 2012–2013 and 2014–2015 leaf‐growing seasons, which had different environmental conditions. Results Leaf shape changed allometrically through developmental stages; early stages were more linear than later stages. There were significant differences in physiognomy in the same developmental stage between the growing seasons, and species had significant differences in mean physiognomy between growing seasons. Phenotypic plasticity was defined as changes between growing seasons after controlling for developmental stage or after averaging all developmental stages. Vitis amurensis and V. riparia had the greatest phenotypic plasticity. North American species exhibited significant differences in tooth area:blade area. Intermediate developmental stages were most likely to exhibit phenotypic plasticity, and only V. amurensis exhibited phenotypic plasticity in later developmental stages. Conclusions Leaves have variable phenotypic plasticity along the vine. Environmental signal was strongest in intermediate developmental stages. This is significant for leaf physiognomic‐paleoclimate proxies because these leaves are likely the most common in leaf litter and reflect leaves primarily included in paleoclimate reconstructions. Early season and early developmental stages have the potential to be confounding factors but are unlikely to exert significant influence because of differential preservation potential.

18PREMISE OF THE STUDY: The size and shape (physiognomy) of woody, dicotyledonous 19 angiosperm leaves are correlated with climate and these relationships have been used to develop 20 paleoclimate proxies. These proxies assume that leaf morphology plastically responds to 21 meteorological conditions and that leaf traits change isometrically through development. 22 METHODS:We used Digital Leaf Physiognomy (DiLP) to measure leaf characters of multiple 23Vitis species from the USDA Germplasm Repository in Geneva, NY from the 2012-2013 and 24 2014-2015 growing seasons. These growing seasons had different temperature and precipitation. 25 KEY RESULTS: We found three primary results: (1) there were predictable significant 26 differences in leaf characters in leaves of different developmental stages along the vine, (2) there 27 were significant differences in leaf characters in leaves of the same developmental stage between 28 the growing seasons, and (3) there were significant differences in leaf characters between 29 growing seasons. 30 CONCLUSIONS:We found that Vitis leaf shape had the strongest relationship with growing 31 season meteorological conditions in taxa growing in their native range. In addition, leaves have 32 variable phenotypic plasticity along the vine. We interpret that the meteorological signal was 33 strongest in those leaves that have completed allometric expansion. This is significant for leaf 34 physiognomic-paleoclimate proxies because these leaves are most likely to be preserved in leaf 35 litter and reflect the type of leaves included in paleoclimate reconstructions. We found that leaf 36 development does have the potential to be a confounding factor, but it is unlikely to exert a 37 significant influence on analysis due to differential preservation potential. 38 39 Keywords: paleoclimate proxy, phenotypic plasticity, Vitis, leaf development, leaf physiognomy 40 41

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