Research finds nothing to indicate that Staghorn sumac (Rhus typhina) is a toxic plant or that the fruit is toxic. It does contain a lot of tannic acid which would make it quite bitter. The only recipe found is in the book Edible and Useful Plants of Texas and the Southwest: A Practical Guide by Delena Tull. It is for making a beverage, Sumac-ade, from the fruit. Rinse the fruit, bruise it with the back of a spoon, and soak in enough warm water (not hot, as that would release a lot of tannin) to cover them. Soak for 30 minutes, strain, and sweeten with sugar or honey. That sure sounds like a lot of trouble to get something that tastes similar to lemonade. Make sure you know the difference between your varieties of sumac, especially poison sumac. For a full description of the plantd and excellent photos, visit the website: Staghorn Sumac.