Thanks, I never thought of cattail...

To extract the flour or starch from the cattail root, simply collect the roots, wash, and peel them. Next, break up the roots under water. The flour will begin to separate from the fibers. Continue this process until the fibers are all separated and the sweet flour is removed. Remove the fiber and pour off the excess water.
Allow the remaining flour slurry to dry by placing near a fire or using the sun.

And lots of other cat tail uses on this website:
[link to www.backwoodshome.com]