| Summary: | Atmospheric carbon dioxide (CO<sub>2</sub>) concentrations are increasing and may exceed 800 ppm by 2100. This is increasing global mean temperatures and the frequency and severity of heatwaves. Recently, we showed for the first time that the combination of short-term warming and elevated carbon dioxide (eCO<sub>2</sub>) caused extreme upward bending (i.e., hyponasty) of leaflets and leaf stems (petioles) in tomato (<i>Solanum lycopersicum</i>), which reduced growth. Here, we examined additional species to test the hypotheses that warming + eCO<sub>2</sub>-induced hyponasty is restricted to compound-leaved species, and/or limited to the Solanaceae. A 2 × 2 factorial experiment with two temperatures, near-optimal and supra-optimal, and two CO<sub>2</sub> concentrations, ambient and elevated (400, 800 ppm), was imposed on similarly aged plants for 7–10 days, after which final petiole angles were measured. Within Solanaceae, compound-leaf, but not simple-leaf, species displayed increased hyponasty with the combination of warming + eCO<sub>2</sub> relative to warming or eCO<sub>2</sub> alone. In non-solanaceous species, hyponasty, leaf-cupping, and changes in leaf pigmentation as a result of warming + eCO<sub>2</sub> were variable across species.
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