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Scientific classification
Dicotyledons or dicots are flowering plants whose seed contains two embryonic leaves or cotyledons. Dicotyledonous plant species are placed in the Class Magnoliophyta. Flowering plants, or angiosperms, that are not dicotyledonous are monocotyledonous: having one embryonic leaf. See How to distinguish a monocot from a dicot for other characteristics thast separate these two groups.

It is believed that monocots evolved from dicots, and as such the latter form a paraphyletic group, i.e. they include some forms which 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 other flowering plants by the structure of their pollen. Basal dicots and monocots have monosulcate pollen, or forms derived from it, whereas eudicots have tricolpate pollen, or derived forms.

Traditionally the dicots have been treated as a class, originally called the Dicotyledoneae, but more recently called Class Magnoliopsida after the type genus Magnolia. Some botanists, however, divide the dicots into two or more classes in an effort to create monophyletic groups. 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 and those under the older Cronquist system, which is still in wide use.

Orders typical of newer systems Cronquist system
Basal dicots Basal eudicots Basal rosids Eurosids I Eurosids II Basal asterids Euasterids I Euasterids II Magnoliidae (mostly basal dicots) Hamamelidae Caryophyllidae Dilleniidae Rosidae Asteridae