BRASSICACEAE (CRUCIFERAE) (Mustard Family)

Contributed by Ihsan A. Al-Shehbaz and George Yatskievych

Plants annual or perennial herbs, rarely woody at the base or shrubby. Leaves alternate or basal, rarely opposite or whorled, lacking stipules, entire to deeply lobed or compound. Inflorescences terminal (except in some species of Lepidium), short to elongate racemes or panicles, or reduced to single, long-stalked flowers (in Leavenworthia). Flowers mostly actinomorphic, perfect. Calyces of 4 free or rarely united sepals. Corollas of 4 free petals, these uncommonly reduced or absent, often narrowed to stalklike bases. Stamens (2, 4)6, often the outer 2 shorter than the inner 4. Ovary 1 per flower, superior, of 2 fused carpels, usually with 2 locules. Style 1 per flower, persistent in the fruits, the stigma 1, entire or 2-lobed. Ovules 1 to numerous. Fruits uncommonly indehiscent and achenelike or more commonly 2-valved capsules that dehisce longitudinally leaving a persistent replum (the thin, placental band of tissue around the periphery of the septum, the partition between the 2 locules), these arbitrarily referred to as siliques when more than 3 times as long as wide or silicles when less than 3 times as long as wide. Seeds variously shaped, with curved embryos. About 350 genera, about 3,500 species, worldwide, but most diverse in temperate and alpine regions and dry areas.

The petals of most species of Brassicaceae are arranged in the shape of a cross, leading to the common name crucifer and the familial name Cruciferae. The family contains a large number of economically important species, both beneficial plants cultivated for food and oils and detrimental weeds. Although separate keys to flowering and fruiting material are given, most species flower for long enough that flowers and fruits are present at the same time. It is recommended that both keys are used, and a more reliable determination to the genus is achieved when both keys are successfully used to reach to the same genus.

An important character of the fruits is whether they are circular in cross-section, 4-angled, or slightly to strongly flattened. If flattened, they can be flattened parallel or at a right angle to the septum. In parallel-flattened fruits, the septum is a broad band of tissue between the 2 faces (valves) extending the full width of the fruit, and the replum is visible as a line along the edge of each face. In fruits flattened at a right angle, the septum is a narrow line of tissue bisecting each face, and the replum is visible as a line along the middle of the face. Such fruits sometimes also have lines or wings along the margins and are almost always shorter than 3 times as long as wide.