Leaf heat tolerance of V. gaultherioides . The controlled heat exposure took place on 24 July 2012 on Mt. Patscherkofel (1950 m a.s.l.). Viability assays were performed two days later. Heat tolerance (LT50) of detached leaves (ex situ) as assessed by computer based visual assessment (VAC) did not differ from results assessed by the visual estimation method (VEM), confirming that for experienced users assessment of leaf injury by visual estimation may represent a fast and viable method to assess heat damage of attached leaves. When the heat treatment was conducted in situ heat tolerance was significantly higher than heat tolerance that was measured on detached leaves. In both cases the controlled heat exposure took place in darkness. Boxes: median, upper and lower quartile. Whiskers: maximum, minimum. Significant differences between mean values of heat tolerance based on ANOVA and the Bonferroni - test and are indicted by different letters (P < 0.01).