Description from Flora of China
Herbs annual, biennial, or perennial, sometimes subshrubs or shrubs, with a pungent, watery juice. Eglandular trichomes unicellular, simple, stalked or sessile, 2- to many forked, stellate, dendritic, or malpighiaceous (medifixed, bifid, appressed), rarely peltate and scalelike; glandular trichomes multicellular, with uniseriate or multiseriate stalk. Stems erect, ascending, or prostrate, sometimes absent. Leaves exstipulate, simple, entire or variously pinnately dissected, rarely trifoliolate or pinnately, palmately, or bipinnately compound; basal leaf rosette present or absent; cauline leaves almost always alternate, rarely opposite or whorled, petiolate or sessile, sometimes absent. Inflorescence bracteate or ebracteate racemes, corymbs, or panicles, sometimes flowers solitary on long pedicels originating from axils of rosette leaves. Flowers hypogynous, mostly actinomorphic. Sepals 4, in 2 decussate pairs, free or rarely united, not saccate or lateral (inner) pair saccate. Petals 4, alternate with sepals, arranged in the form of a cross (cruciform; hence the earlier family name Cruciferae), rarely rudimentary or absent. Stamens 6, in 2 whorls, tetradynamous (lateral (outer) pair shorter than median (inner) 2 pairs), rarely equal or in 3 pairs of unequal length, sometimes stamens 2 or 4, very rarely 8-24; filaments slender, winged, or appendaged, median pairs free or rarely united; anthers dithecal, dehiscing by longitudinal slits. Pollen grains 3-colpate, trinucleate. Nectar glands receptacular, highly diversified in number, shape, size, and disposition around base of filaments, always present opposite bases of lateral filaments, median glands present or absent. Pistil 2-carpelled; ovary superior, sessile or borne on a distinct gynophore, mostly 2-locular and with a false septum connecting 2 placentae; placentation parietal, rarely apical; ovules anatropous or campylotropous, bitegmic, 1 to many per locule. Fruit typically a 2-valved capsule, generally termed silique (siliqua) when length 3 × or more than width, or silicle (silicula) when length less than 3 × width, dehiscent or indehiscent, sometimes schizocarpic, nutletlike, lomentaceous, or samaroid, segmented or not, terete, angled, or flattened parallel to septum (latiseptate) or at a right angle to septum (angustiseptate); valves 2(or 3-6); replum (persistent placenta) rounded, rarely flattened or winged; septum complete, perforated, reduced to a rim, or lacking; style 1, distinct, obsolete, or absent; stigma capitate or conical, entire or 2-lobed, sometimes lobes decurrent and free or connate. Seeds without endosperm, uniseriately or biseriately arranged in each locule, aseriate when 1, winged or wingless, mucilaginous or not when wetted; cotyledons incumbent (embryo notorrhizal: radicle lying along back of 1 cotyledon), accumbent (embryo pleurorrhizal: radicle applied to margins of both cotyledons), or conduplicate (embryo orthoplocal: cotyledons folded longitudinally around radicle), rarely spirally coiled (embryo spirolobal). Germination epigeal.
Because of lack of a comprehensive classification based on phylogenetic relationships among genera, and in order to facilitate direct comparison between the accounts in FOC and FRPS, the sequence of genera follows Schulz (Nat. Pflanzenfam. 17b: 227-658. 1936). However, it should be emphasized that his system is largely artificial because he placed closely related genera in different tribes and remotely related genera in the same tribe. For example, Arabis, Aubrieta, Draba, and Macropodium, which are very closely related on the basis of recent molecular studies, were placed by Schulz in four different tribes, whereas the unrelated Capsella, Lepidium, and Thlaspi were placed in one tribe. The delimitation of genera is often difficult, and mature fruits are needed for reliable identification.
The Brassicaceae include many important crop plants that are grown as vegetables (Brassica, Nasturtium, Raphanus) and sources of vegetable oils (Brassica) and condiments (Armoracia, Brassica, Eutrema, Sinapis). Oils of Brassica probably rank first in terms of tonnage of the world's production of edible oils. The family includes many ornamentals in the genera Erysimum, Iberis Linnaeus, Lobularia, Malcolmia, and Matthiola. Of these, only Lobularia maritima has become naturalized in China. The family also includes more than 120 species of weeds. Arabidopsis thaliana, which is naturalized in China, has become the model organism in many fields of experimental biology.
The delimitation of genera in the Brassicaceae is often difficult because of the frequent independent evolution of what appear to be similar character states, the variability of a given character in one genus and its fixture in another, and the inadequate sampling of material by most authors. Fruit characters are essential in the identification of genera. However, a key emphasizing flowering material is given in addition to the one emphasizing fruit. The most reliable determination of genera can be achieved when the material has both fruit and flowers and when both keys are successfully used to reach the same genus.
The types of cotyledonary position, which in reality is the position of the radicle in relation to the cotyledons (e.g., radicle accumbent, incumbent, or conduplicate, though radicle referred to as "cotyledon" throughout) are important in the separation of many genera, and a cross section of the seed provides the easiest and simplest way of determining that position. The exact number of ovules per ovary can easily be determined from the fruit because aborted ovules persist through fruit dehiscence. However, it is more laborious to determine the ovule number from pistils and young fruit.
Cheo Tai-yien, Guo Rong-lin, Lan Young-zhen, Lou Lian-li, Kuan Ke-chien & An Zheng-xi. 1987. Cruciferae. In: Cheo Tai-yien, ed., Fl. Reipubl. Popularis Sin. 33: 1-483.
Leads marked with a "double asterisk" (**) indicate that mature fruits are necessary for the identification of genera in the subordinate couplet(s).
About 330 genera and 3500 species: all continents except Antarctica, mainly in temperate areas, with highest diversity in Irano-Turanian, Mediterranean, and W North American regions; 102 genera (eight endemic) and 412 species (115 endemic) in China.
(Authors: Zhou Taiyan (Cheo Tai-yien), Lu Lianli (Lou Lian-li), Yang Guang; Ihsan A. Al-Shehbaz2)