Brassicales

Brassicales, order of flowering plants that includes cabbages and capers, as well as mignonette, mustard, and nasturtiums. Brassicales includes 17 families, 398 genera, and 4,450 species. There are five family groups: Brassicaceae, Capparidaceae, and Cleomaceae; Akaniaceae and Tropaeolaceae; Caricaceae and Moringaceae; Bataceae, Salvadoraceae, and Koeberliniaceae; and Resedaceae, Gyrostemonaceae, Tovariaceae, and Pentadiplandraceae. Not clearly placed are Limnanthaceae, Setchellanthaceae, and Emblingiaceae.

The order is very distinct anatomically, ultrastructurally, and chemically, as well as being recognizable easily in molecular comparisons. Indeed, the smell and taste of the plants in Brassicales result from the presence of glucosinolates—sulfur-containing compounds that are also known as mustard oils. These compounds are found in nearly every member of the order and can deter the depredations of everything from bacteria to mammals. However, these same compounds may attract other species. Butterflies of the genus Pieris and its relatives (cabbage whites and orange tips) are attracted to members of Brassicaceae in particular, and they can be very serious pests of cultivated Brassica. Indeed, Brassicaceae is often heavily attacked by dermestid beetles and other herbarium pests, while the related Resedaceae, for example, is largely pest-free. Only one family outside the Brassicales order, Putranjivaceae of the order Malpighiales, is known to have glucosinolates. One family in Brassicales, Koeberliniaceae, does not have glucosinolates, though other evidence firmly places it in that order.

Most members of Brassicales have racemose inflorescences, and the leaves have small stipules. The flowers often do not have the regular n sepals, n petals, 2n stamens, and n carpels arrangement so common in other Rosids. In many Brassicales, the nectary is found between the petals and the stamens, the usual position being between the stamens and the ovary. Green embryos are also common.

Most of the members of Brassicales have long been recognized as being related, although some botanists are still inclined to place Akaniaceae with Sapindaceae, the two being superficially (though not chemically) similar. Limnanthaceae is sometimes associated with the Asterid I group, and Gyrostemonaceae has been placed with Caryophyllales. Families like Brassicaceae that have ovules borne on the walls of the ovary have often been linked to Papaveraceae (order Ranunculales) and other families with similar ovaries; however, the relationship is not at all close.