I say that I have tried every way I know to 'use' the burning staff
I acquired in the Rattkin tree. I have had it equipped and also in my inventory for my ranger. The item does not show up to try and use.
(Pardon the EverSpeak coming up) Does this item 'proc'? I have not seen another item that does this. Anyway, I am prepared for the upcoming proof that I am an idiot and this is wonderfully simple and intuitive to use...

LOL!
have you equipped it and just used it? you know, made it your primary weapon?

that's what i do, and after the 1st time it's used in battle, it throws up the Ring of Fire. you will know it's working, because you get an in-window msg and there's an icon in the upper right of the screen, next to the "Bless" icon. it's an orange, fiery looking symbol. :D

also it causes the fire damage at the end of the round. the last message in every round will be "Poison Seeker takes 6 dmg from Ring of Fire" for each of the baddies.

ps: i dunno how often your ranger will use it, since they can use the bow in close combat. try giving it to a fighter, priest or valk to see it in action!

Don't waste a good weapon other than the best bow on your ranger, he can use his bow at any range, give Staves and other weapons of the like to your priest/bishop to use from the middle of the pack.