What spice, made from ground sassafras leaves, is used to thicken gumbo?

The spice made from ground sassafras leaves and used to thicken gumbo is filé powder.

Filé powder, also called gumbo filé, is produced from the dried and ground leaves of the North American sassafras tree, Sassafras albidum. It contributes an earthy flavor and can give gumbo a thicker, slightly stringy texture.

Its use is strongly connected to Choctaw culinary traditions. Native peoples in the southeastern United States used ground sassafras leaves as a seasoning and soup thickener, and the ingredient became part of Louisiana Creole cooking. The word filé comes from French and refers to becoming threadlike or ropy.

Filé powder is generally stirred into gumbo after cooking or sprinkled over individual servings. Adding it while the pot is boiling can make the texture overly ropey. Gumbo may instead be thickened with roux or okra, so filé is a characteristic option rather than a universal ingredient in every gumbo recipe.