Filé powder is the dried, finely ground young leaf of Sassafras albidum, the North American sassafras tree, and it is the defining thickener and seasoning of Louisiana Creole and Cajun gumbo. Its name comes from the French filer, to spin or draw into threads, describing the ropy, mucilaginous strands it forms when stirred into hot liquid. A Choctaw invention of the Gulf South, filé was adopted wholesale into Creole cooking as one of three traditional ways to thicken and flavour gumbo — alongside a dark roux and okra — and it contributes a distinctive earthy, root-beer-and-eucalyptus aroma with a faint sour-lemony edge. Because heat makes it turn stringy and gummy, filé is almost always stirred in off the fire, at the table or just before serving, rather than cooked in the pot.