Pumpkin pie is a dessert pie with a spiced, pumpkin-based custard filling. The pumpkin is a symbol of harvest time, and pumpkin pie is often eaten during the fall and early winter. In the United States and Canada, it is usually prepared for Thanksgiving, and other occasions when pumpkin is in season. The pie filling ranges in color from orange to brown, and is baked in a single pie shell, rarely with a top crust. The pie is generally flavored with cinnamon, powdered ginger, nutmeg, and cloves. Allspice is also commonly used and can replace the clove and nutmeg, as its flavor is similar to both combined. Cardamom and vanilla are also sometimes used as batter spices. The spice mixture is called pumpkin pie spice. The pie is often made from canned pumpkin or packaged pumpkin pie filling (spices included), mainly from varieties of Cucurbita moschata.