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Dicotyledon


 

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Dicotyledons or "dicots" are flowering plants whose seed typically contains two embryonic leaves or cotyledons. Flowering plants that are not dicotyledons are monocotyledons, typically having one embryonic leaf.

Related Topics:
Flowering plant - Seed - Cotyledon - Monocotyledon

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It is now known from genetic research by the Angiosperm Phylogeny Group that monocotyledons evolved from within the dicotyledons, and as such the latter form a paraphyletic group, i.e. they include some groups that are as closely related to monocots as they are to the other dicots. The vast majority, however, form a monophyletic group called the eudicots or tricolpates. These may be distinguished from all other flowering plants by the structure of their pollen. Other dicotyledons and monocotyledons have monosulcate pollen, or forms derived from it, whereas eudicots have tricolpate pollen, or derived forms, the pollen having three or more pores set in furrows called colpi.

Related Topics:
Angiosperm Phylogeny Group - Paraphyletic - Monophyletic - Eudicots - Pollen - Monosulcate

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Traditionally the dicots have been called the Dicotyledones (or Dicotyledoneae), at any rank. If treated as a class, as in the Cronquist system, they may be called the Magnoliopsida after the type genus Magnolia. In some schemes, the eudicots are treated as a separate class, the Rosopsida (type genus Rosa), or as several separate classes. The remaining dicots (palaeodicots) may be kept in a single paraphyletic class, called Magnoliopsida, or further divided.

Related Topics:
Type genus - Magnolia - Palaeodicots

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The classification of dicots has undergone considerable revision as our understanding of their relationships has changed, and is still not entirely settled, though a general consensus is emerging. The following lists are of the orders typical of new classification systems (primarily that of the Angiosperm Phylogeny Group) and those under the older Cronquist system, which is still in wide use.

Related Topics:
Angiosperm Phylogeny Group - Cronquist system

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Orders typical of newer systems

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Cronquist system

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'Palaeodicots': basal orders

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