Family

Family is the taxonomic rank between order and genus. A number of related genera make up one family. A number of related families are then grouped into an order, a higher rank that therefore represents a larger group of plants. A family may include only one genus and one species or hundreds of genera and several thousand species. A large family may be further organized using the rank of subfamily, with related genera grouped into sub-families, then subfamilies into families.

In the past, families and subfamilies were just groups of genera that shared some similar features, especially of the flower and fruit. Such groupings often omitted closely related plants that looked different. Beginning in the late twentieth century, botanists have come to think that families should be natural groups. A natural group, which includes all the descendants of some common ancestor, is based on evolutionary relationships, not just similar appearance.

Names of families can be recognized by the ending "-aceae." Each family has a type genus, a representative genus that defines that family, and the family's name is formed by adding -aceae to the name of that genus. For example, Primulus (primrose) is the type genus of the family Primulaceae, or primrose family.