Magnoliopsida

(botany) The dicotyledons, a class of flowering plants in the division Magnoliophyta generally characterized by having two cotyledons and net-veined leaves, with vascular bundles borne in a ring enclosing a pith.

One of the two classes of flowering plants which collectively make up the division Magnoliophyta (Angiospermae). The Magnoliopsida, often known as Dicotyledoneae or dicotyledons, embrace 6 subclasses, 64 orders, 318 families, and about 165,000 species.

All of the characters which collectively distinguish the Magnoliopsida from the Liliopsida (monocotyledons) are subject to exception, but in general the Magnoliopsida have two cotyledons and net-veined leaves. The vascular bundles are typically borne in a ring (or cylinder) enclosing a pith. Increase in thickness of stems and roots, after the primary tissues have matured, results from meristematic activity of a cambial layer which passes through the vascular bundles. In about half of the species of the group, the cambium of the stem forms a continuous cylinder which produces a new layer of wood (secondary xylem) and bark (secondary phloem) each growing season for year after year. Such plants become trees or shrubs.

It is widely agreed that the most existing angiosperms belong to the dicotyledons (especially the order Magnoliales) and that most of the characters which distinguish the monocotyledons as a group are derived rather than primitive. See also Asteridae; Caryophyllidae; Dilleniidae; Hamamelidae; Liliopsida; Magnoliales; Magnoliidae; Magnoliophyta; Plant kingdom; Rosidae.

The noun has one meaning:

Meaning #1: comprising seed plants that produce an embryo with paired cotyledons and net-veined leaves; divided into six (not always well distinguished) subclasses (or superorders): Magnoliidae and Hamamelidae (considered primitive); Caryophyllidae (an early and distinctive offshoot); and three more or less advanced groups: Dilleniidae; Rosidae; Asteridae
  Synonyms: Dicotyledones, class Dicotyledones, Dicotyledonae, class Dicotyledonae, class Magnoliopsida

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Magnoliopsida is a valid botanical name for a class of flowering plants. By definition the class will include the family Magnoliaceae, but its circumscription can otherwise vary, being more inclusive or less inclusive depending upon the classification system being discussed.

Magnolia flowers

Contents 1 Cronquist and Takhtajan systems 1.1 Magnoliopsida in the Takhtajan system 1.2 Magnoliopsida in the Cronquist system 2 Dahlgren and Thorne systems 3 Reveal system 4 APG systems

Cronquist and Takhtajan systems

In the Takhtajan system and the Cronquist system the name was used for the group known as dicotyledons.

Magnoliopsida in the Takhtajan system

The Takhtajan system used this internal taxonomy:

• class Magnoliopsida [= dicotyledons]

  subclass Magnoliidae

  subclass Nymphaeidae

  subclass Nelumbonidae

  subclass Ranunculidae

  subclass Caryophyllidae

  subclass Hamamelididae

  subclass Dilleniidae

  subclass Rosidae

  subclass Cornidae

  subclass Asteridae

  subclass Lamiidae

Magnoliopsida in the Cronquist system

The Cronquist system used this internal taxonomy (in the 1981 version):

• class Magnoliopsida [= dicotyledons]

  subclass Magnoliidae

  subclass Hamamelidae

  subclass Caryophyllidae

  subclass Dilleniidae

  subclass Rosidae

  subclass Asteridae

Dahlgren and Thorne systems

The Dahlgren system and the Thorne system (1992) used the name Magnoliopsida for the flowering plants (angiosperms). However, the Cronquist system has been very popular and there have been many versions of the system published. In some of these Cronquist-based systems the name Magnoliopsida (at the rank of class) refers to the flowering plants (the angiosperms).

• class Magnoliopsida [= angiosperms]

  subclass Magnoliidae [= dicotyledons]

  subclass Liliidae [= monocotyledons]

Reveal system

The Reveal system used the name Magnoliopsida for a group of the primitive dicotyledons, corresponding to about half of the plants in the magnoliids:

• class 1. Magnoliopsida

  superorder 1. Magnolianae

  superorder 2. Lauranae

APG systems

In the APG and APG II systems botanical names are used only at the rank of order and below. Above the rank of order, these systems use their own names, such as angiosperms, eudicots, monocots, rosids, etc. These names refer to clades (unranked). This class Magnoliopsida is not defined. Note that the idea that dicotyledons could be a taxonomic unit and get a formal name is rejected by the APG: the dicots are considered to be paraphyletic.

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