There is a new paper published by Elena Carrió and Josep A. Roselló online early in Molecular Ecology Resources that suggests salt dessication of leaves dehydrates and prevents decay at levels similar to that of silica gel, with similar PCR results.
Large-grain silica is probably still the best option, but this would come in really handy if you come across something interesting that you want to collect but don’t happen to have silica gel with you.
Here is the main figure (link to the paper below):
Thanks to Maggie Wagner from the TMO lab who found this paper and sent it around. Here is a link to the full article: