Leaf heat tolerance of L. procumbens. Heat exposure took place on 26 Sep 2011 on Mt. Patscherkofel (1960 m a.s.l.). Heat tolerance (LT50) determined on detached leaves (ex situ) using the electrolyte leakage test (ELT, dotted box) did not differ from heat tolerance as determined on detached leaves using the computer based visual assessment method (VAC, hatched box). When heat exposure was conducted in situ by the Heat Tolerance Testing System, heat tolerance values (fine dotted box) were significantly higher than heat tolerance values determined on detached leaves. Additionally, when the heat treatment was conducted in situ and under the presence of natural solar irradiation (white box) heat tolerance was significantly higher than compared to the heat tolerance as being determined from the same treatment but in darkness. For both the visual estimation method (VEM) was applied. In all cases viability assessment took place two days after the controlled heat exposure. Boxes: median, upper and lower quartile. Whiskers: maximum, minimum. Significant differences between mean values of heat tolerance based on ANOVA and the Bonferroni - test are indicated by different letters (P < 0.05).