1 - Rumex alpinus
 

A clear night (-6 °C) after a storm was too much for these Rumex alpinus leaves at 2500 m in the Swiss Alps in mid summer. Frozen leaves look like wilting before they get brown - why? One immediate consequence of damaging low temperatures is the disruption of cell membranes. As they become "leaky" the cell pressure (turgor) collapses and leaves lose shape. Such damage does not become visible in mature evergreen leaves, because their shape is determined by thick cell walls and not by turgor.

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