What is traditionally the main fruit ingredient in Black Forest cake?

Typically, Black Forest cake consists of several layers of chocolate cake, with whipped cream and cherries between each layer. Then the cake is decorated with additional whipped cream, maraschino cherries, and chocolate shavings. In some European traditions sour cherries are used both between the layers and for decorating the top.

The cake is named not directly after the Black Forest (Schwarzwald) mountain range in southwestern Germany but rather from the specialty liquor of that region, known as Schwarzwälder Kirsch(wasser) and distilled from tart cherries. This is the ingredient, with its distinctive cherry pit flavor and alcoholic content, that gives the cake its flavor. Cherries, cream, and Kirschwasser were first combined in the form of a dessert in which cooked cherries were served with cream and Kirschwasser, while a cake combining cherries, cookies / biscuits and cream (but without Kirschwasser) probably originated in Germany.