Hey Parnell,
Break/bruise a piece of that. If it has a strong aromatic quality, its Dog Fennel. I get a bunch of it here. I need to get some goats, they love it, and the cows won't touch it. I don't have a clue if it is good arrow material, let me know if it is. We do have giant reed and elephant grass in the area (I've got that on my property as well).
Swamp
ETA: Dog fennel not dog bane, musta been on auto pilot when I posted originally.