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.

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.

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.

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.

Orders typical of newer systems

Cronquist system

'Palaeodicots': basal orders Amborellales Nymphaeales Austrobaileyales Chloranthales Ceratophyllales 'Palaeodicots': Magnoliid complex Magnoliales Laurales Piperales Aristolochiales Canellales Eudicots Basal eudicots Ranunculales Buxales Trochodendrales Proteales Gunnerales Berberidopsidales Dilleniales Caryophyllales Saxifragales Santalales Vitales Rosids Basal rosids Crossosomatales Geraniales Myrtales Eurosids I Zygophyllales Celastrales Malpighiales Oxalidales Fabales Rosales Cucurbitales Fagales Eurosids II Brassicales Malvales Sapindales Asterids Basal asterids Cornales Ericales Euasterids I Garryales Solanales Gentianales Lamiales Unplaced: Boraginaceae Euasterids II Aquifoliales Apiales Dipsacales Asterales

Magnoliopsida Magnoliidae (mostly basal dicots) Magnoliales Laurales Piperales Aristolochiales Illiciales Nymphaeales Ranunculales Papaverales Hamamelidae Trochodendrales Hamamelidales Daphniphyllales Didymelales Eucommiales Urticales Leitneriales Juglandales Myricales Casuarinales Caryophyllidae Caryophyllales Polygonales Plumbaginales Dilleniidae Dilleniales Theales Malvales Lecythidales Nepenthales Violales Salicales Capparales Batales Ericales Diapensiales Ebenales Primulales Rosidae Rosales Fabales Proteales Podostemales Haloragales Myrtales Rhizophorales Cornales Santalales Rafflesiales Celastrales Euphorbiales Rhamnales Polygalales Sapindales Geraniales Apiales Asteridae Gentianales Solanales Lamiales Callitrichales Plantaginales Scrophulariales Campanulales Rubiales Dipsacales Calycerales Asterales

Compared to Monocotyledons

Seeds: The embryo of the monocot has one cotyledon while the embryo of the dicot has two.

Flowers: The flower parts in monocots are multiples of three while in dicots are multiples of four or five.

Stems: In monocots, the stem vascular bundles are scattered, while in dicots there are in a ring.

Pollen: In monocots, pollen has one furrow or pore while in dicots they have three.

Roots: The roots are adventitious in monocots, while in dicots they develop from the radicle.

Leaves: In monocots, the major leaf veins are parallel, while in dicots they are reticulated.