Dicotyledon

The dicotyledons or dicots ( Dicotyledoneae, Magnoliatae ) were one of two traditional classes of angiosperms ( Magnoliophyta) and were defined according to the number of cotyledons of the other class, the monocots. However, unlike the monocots the dicotyledons are no natural kinship group, which is why they were separated in the two groups Magnoliopsida ( Magnoliopsida ) and three furrows pollen dicots or Eudikotyle ( Rosopsida ).

Features

The eponymous feature is the number of two cotyledons, which, with few exceptions (such Degeneria with three to four) applies to all representatives. The vascular bundles in the stem axis are formed as Eustele, so arranged in a circle. Secondary growth by means of cambium is often the case.

The roots are usually durable ( Allorhizie ) and have a oligarches vascular bundles. The leaves are varied, usually they have a distinct petiole and have a reticulate venation. They often have stipules, rarely leaf sheaths.

The flowers are usually arranged in five (four ) zähligen whorls, the perianth is often differentiated into calyx and corolla. Two - or three-fold whorls are rare, as is a schraubige position. The Pollentetraden are usually formed simultaneously, the pollen grains usually have three furrows ( tricolpate ). The endosperm is formed in the nucleus or cellular, but never typical helobial.

The original and widespread form of life is the tree. Herbaceous forms are considered to be derived.

At chemical characteristics are: high incidence of ellagic acid and ellagitannins, condensed and hydrolysable tannins, essential oils, of triterpene acids from polyterpenes (like rubber), of alkaloids, triterpene saponins, of calcium oxalate in the form of drusen, and of slimes with Uronsäurekomponente.

Botanical history

John Ray in 1682 the first to recognize that not all seed plants about two cotyledons. In 1703 he shared the angiosperms in the two groups Dicotyledones and Monocotyledones. Antoine Laurent de Jussieu has the structure adopted in 1778 and 1789 used in his work Genera Plantarum. This dichotomy remained until the 1990s obtained when it was realized that the dicots do not form a natural affinity group ( are not monophyletic ). The basal groups of angiosperms were separated from the actual " Eudikotylen " and are called Magnoliopsida. The Eudikotylen are monophyletic, while the dicots are paraphyletic Magnoliopsida still.

Sources and further information

• P. Sitte, H. Ziegler, F. Ehrendorfer, A. Bresinsky: textbook of botany for colleges. G. Fischer Verlag, Stuttgart, Jena, New York, 1991, pp. 761f. ISBN 3-437-20447-5