Description
The family consists mostly of herbaceous plants with annual, biennial or perennial lifespans. However, around the Mediterranean they include also a dozen woody shrubs 1m - 3m tall, e.g. in northern Africa (Zilla spinosa and Ptilotrichum spinosum), in the Dalmatian islands (Dendralyssum and Cramboxylon), and chiefly in Canarias with some woody cruciferous genera: Dendrosinapis, Descurainia, Parolinia, Stanleya, etc..
The leaves are alternate (rarely opposite), sometimes organized in basal rosettes; in rare shrubby crucifers of Mediterranean their leaves are mostly in terminal rosettes, and may be coriaceous and evergreen. They are very often pinnately incised and do not have stipules.
The structure of the flowers is extremely uniform throughout the family. They have four free saccate sepals and four clawed free petals, staggered. They can be disymmetric or slightly zygomorphic, with a typical cross-like arrangement (hence the name 'Cruciferae'). They have six stamens, four of which are longer (as long as the petals, so relatively short in fact) and are arranged in a cross like the petals and the other two are shorter (tetradynamous flower). The pistil is made up of two fused carpels and the style is very short, with two lobes. Superior ovary. The flowers form ebracteate racemose inflorescences, often apically corymb-like.
Pollination occurs by entomogamy, nectar is produced at the base of the stamens and stored on the sepals.
The fruit is a peculiar kind of capsule named siliqua (plural siliquae, American English silique/siliques). It opens by two valves, which are the modified carpels, leaving the seeds attached to a framework made up of the placenta and tissue from the junction between the valves (replum). There is often an indehiscent beak at the top of the style and one or more seeds may be borne there. Where a siliqua is less than three times as long as it is broad, it is usually termed a silicula. The siliqua may break apart at constrictions occurring between the segments of the seeds, thus forming a sort of loment (e.g., Raphanus), it may eject the seeds explosively (e.g., Cardamine) or may be evolved in a sort of samara (e.g., Isatis). The fruit is often the most important diagnostic character for plants in this family.
Brassicaceae do not form mycorrhizae, although rare exceptions do exist.
Most members share a suite of glucosinolate compounds that have a typical pungent odour usually associated with cole crops.
Read more about this topic: Brassicaceae
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