This family might be easier to remember by its alternative name, Cruciferae, meaning 'cross-bearing', a reference to its cross-shaped flowers. There are eight families with alternative names. In each case, the irregular name refers to a distinctive feature, or familiar name. The regularly formed names, those ending in -aceae, are, of course, based on the name of one of the genera in the family. Brassicaceae is based on the name of one of the family's familiar genera, Brassica, whichncludes of cabbage, cauliflower, broccoli, mustard, turnips, rape (source of canola oil), etc. Clearly not a trivial genus, but the name Brassicaceae is not as evocative of the family's characteristics as Cruciferae.

The list above suggests, as is the truth, that the family is economically important. It is important for crop plants, oil seed (B. rapa, rape, is the source of canola oil), animal feed, condiments, and several ornamental plants (Alyssum, Erysimum [= wallflowers], Arabis [= rock cress], and many more). The family is one of the relatively few that is most abundant in the north temperate regions, although it occurs throughout the world. Its greatest abundance is around the Mediterranean, and in southwestern and central Asia.

Almost all members of the family are annual or perennial herbs, with alternate, estipulate leaves. Many members are pubescent, some with forked, stellate, or malpighian (pickaxe-like) hairs.

It is the flowers that make the Brassicaceae one of our easier families to recognize. They are (usually) radially symmetric, with 4 sepals, 4 petals, 6 stamens (2 short and 4 long), and a single bilocular pistil having parietal placentation. 

So what is so distinctive? First of all, there are not that many 4-merous families. Also, there is no other 4-merous family with 6 stamens, and no other family with the combination of 2 locules and parietal placentation. The 6 stamens are also unusual in being of two lengths, 4 long and 2 short.  Of course, a species that lacks one of these characteristics may still be a member of the family, but it should have most of them.

For accurate identification of members of the Brassicaceae, it is almost essential to have mature fruit. These fruits are  distinctive because the outer walls of the ovary usually fall off at maturity, leaving behind the internal wall, known as the replum. The fruits tend to be long and narrow, in which case they are called siliques, or relatively short and wide, in which case they are called silicles. Next time you see a silver dollar plant, make yourself decide what it is you are looking at when you examine the "silver dollar".