I have been reading up on cattails as food. Even for human consumption, the entire plant is edible. Leaves are tough, the white core is sweet... described kinda like asperagus, zuchini, or cucumber (peeled and chopped for salads or soups), and the root is supposed to be starchy like a potatoe. My buns had a mound of grape vine tossed in an hour ago, and some was still there when I checked on them. I tossed in a few whole cattails, and everybunny came running. They prefer this sweet treat to grapevine, devouring the long leaves first then the core. I have yet to see if they prefer this to willow. I'll try drying a bunch for winter feeding since I have been able to find so much of it (MaggieJ, it's all over the base and the parks where I bring the kids! I love finding free bunny food). I noticed your list notes only the leaves, but I wonder if it could be changed to entire plant (the favored part being the leaves). I'm not sure where to find it's value as a protien source (I wonder if it is as valuable as willow. One site lists just basic nutritional blurb).
I did find one draw-back for using cat tails as a food... they filter the water they are in, and so are filled with whatever was in the water (ewwwww, ditch run off). So, perhaps it's best to consider where your water supply is coming from before consuming... (sorry MaggieJ, I never considered this before harvesting those for your bunnies. Perhaps I could bring you some from the beach where I know they test the water regularly).
I had also wondered about elephant grass, as it seems to be everywhere and there MUST be a purpose for it. Has anyone looked into it? I could only find one mention of it as an undesired food source, perhaps better for bedding.