The phrase "mustard family" refers to a group of plants that belong to the same family as mustard plants. These plants have similar characteristics and are often used for various purposes, such as food, spices, and medicine. Full definition
And while it can be bitter (it comes from the mustard family which includes turnips), with some careful preparation I've never found it to be so. (ahintofhoney.com)
A: Horseradish is a root, similar to wasabi, and a member of the mustard family. (fieryfoodscentral.com)
Wasabi (Wasabia japonica) is a perennial plant, a member of the mustard family, and a cousin to cruciferous vegetables such as cabbage, broccoli and cauliflower. (fieryfoodscentral.com)