In biological classification, a family (, plural ) is a taxonomic rank between order, and genus. A family may be divided into one or more subfamiles, intermediate ranks above the rank of genus. In vernacular usage, a family may also be named after one of its common members, e.g. walnuts and hickory trees belong to the family Juglandaceae, commonly known as the walnut family. What does and does not belong to each family is determined by a taxonomist — as is whether a particular family should be recognized at all. Often there is no exact agreement, with different taxonomists taking different positions. There are no hard rules that a taxonomist needs to follow in describing or recognizing a family. Some taxa are accepted almost universally, while others are recognised only rarely.