lingonberries
Small red forest berries from northern Europe, tart and sour with a slightly bitter edge, usually eaten cooked down with sugar.
Lingonberry jam or preserves are sold in many supermarkets and Scandinavian shops, while fresh or frozen berries turn up only in late summer at markets, in Scandinavian or Eastern European shops, or by mail order. Berries sold as "cultivated lingonberries" in German-speaking countries are usually cranberries.
Substitute:
Cranberries come closest but are larger, more sour and less bitter, and need more sugar when cooked down. Ready-made lingonberry preserves can stand in for home-cooked berries, though they are sweeter.