No, you find the runes and then... attach them to whatever you want to upgrade. [Runes are items, that is.] Plants aren't magic unless we're talking about something that's been possesed. Regular ones are used for crafting potions or venoms, if we're talking about uses in battle...
Otherwise there are plenty that get used for cooking. Stripweed supposedly makes a fantastic tea. Personally? I think we'd be better off burning the whole lot of them.