I've yet to try Rowan leaves, I know in Wales they have made an alcoholic drink from the berries and also Jam! but preserving the leaves would be an interesting experiment, Ill be keeping my eyes peeled for some now however, Nettle Tea is a nice brew to get you moving on a cold morning, though I tend to use Nettles for making cord more than anything else as they're quite strong for shelter making and biodegradable :D