Members of the genus Brassica belong to the mustard family Brassicaceae. The whole family includes a total of 376 different genera and 3,200 different species. The family is also known as "Cruciferae" because the four-petaled flowers of these plants look like crosses. The plants are distributed worldwide and have annual (living one year), biennial (living two years) and perennial (living many years) members. The edible plants in this genus are also distinctive because to some people they have a very bitter taste; the bitterness is due to a useful phytochemical called sulforaphane.
Some common members of the genus Brassica include:
Brassica rapa, whose subspecies include:
Also, one subspecies of B. rapa is used as a model organism to study genetics, molecular biology, plant breeding, cell biology, and physiology; it is called the "rapid cycling" Brassica or RCBr or the Wisconsin Fast Plant™, and was developed specifically for scientific study. Also, the radish Raphanus sativus is a member of the Brassicaceae family.
The full taxonomic classification is kingdom Plantae, division Tracheophyta, subdivision Spermatophyta, class Angiospermae, subclass Dicotyledeonae, order Papaverales, family Brassicaceae.
From the science dictionary at http://biotech.icmb.utexas.edu/