Lungweed

The lungweed is an unassuming reed-like water plant. However, when ground up, mixed with a bonding agent to form a paste, then rubbed into gills, the lungweed allows one who can normally not breathe air to do so for about an hour. It's use is common among members of the various aquatic races who do business on the surface but have no access to more long-lasting (and usually expensive) forms of magical air breathing.