In some species, exposure to HF causes distortion of leaf shape. When fluoride accumulates at the margins and tip of a young, growing leaf it affects cell expansion. The cells away from the zones of accumulation continue to expand, causing distortion. The effects can be very subtle but they are quite clear in this alder (Alnus glutinosa) branch. Note some leaves have near normal shape but most show degrees of distortion. The effect depends on the exact stage of growth of the individual leaves during the fumigation episode. Note that it is unusual to see this degree of distortion in alder; it is of intermediate sensitivity.