Berry plant related to a hawthorn

SLOE

Think of the small, tart fruit used to flavor a classic British gin.

The word "sloe" refers to the small, dark fruit of the blackthorn plant, which is closely related to the hawthorn. Both belong to the same botanical family (Rosaceae), so the clue hints at this connection. If you know that sloes are used in making sloe gin, that might help jog your memory—though the clue itself is straightforward, focusing on the plant relationship.