This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
This very natural group of plants is so well defined that very little difficulty is experienced in recognising its members. They are almost without exception annual or perennial herbs with stellate hairs, radical leaves in rosettes, and the cauline alternate, destitute of stipules. Flowers usually in terminal racemes, rarely solitary, commonly ebracteate. Sepals 4, of which two are often saccate at the base. Petals 4. Stamens 6, tetradynamous (in Megacarpaea polydndra the stamens are numerous). Ovary 2-celled or transversely jointed. Seeds destitute of albumen. This order includes nearly 200 genera and 1,200 species, occurring in all parts of the world, and extending to the polar limits of flowering plants, but especially abundant on the borders of the Mediterranean Sea. It is one of the most important to the vegetable gardener, including as it does the many varieties of cabbage, broccoli, turnip, radish, cress, sea-kale, etc., and nearly all its members are antiscorbutic. It is, moreover, not lacking in ornamental plants, especially in fragrant flowering species.
§ 1. Pod continuous, usually much longer than broad, dehiscing throughout its whole length, or transversely jointed, not com-pressed at right angles to the 'partition.