my observations,
punk wood, is about the best sustainable natural char material you can use. Can be a bit spotty in use, the best spongy, light punk wood once charred is second to none as far as char material goes. But you can get punk wood that is not so 'punky' and this is where it becomes spotty in use.
White punk tinder fungus, is excellent, again some of it will take a spark very easily, then other samples are frustratingly difficult to get to take a spark. Must be bone dry to work properly. Love the fact that you don't have to char it to use it.
cattail heads, my favourite natural tinder besides punk wood. Ember transfer to a cattail head and it will smoulder for a good long time, allows you to travel with an ember that doesn't need a lot of coaxing or maintenance to keep going as they just ember along by themselves.
Cattail fluff, pull the cattail head apart and nitrate the fluff using potassium nitrate and it will take a spark very easily (as easily as char cloth) from flint and steel and burn vigorously, very good prepared tinder. I would use nitrated cattail fluff as often as char cloth, it is so versatile and useful.