Dicotyledon

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Dicotyledon
Lamium album (white dead nettle)
Lamium album (white dead nettle)
Scientific classificationEdit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Spermatophytes
Clade: Angiosperms
Groups included
Cladistically included but traditionally excluded taxa
  • Monocots
Synonyms
  • Dicotyledoneae
  • Magnoliatae
    Takht.[1]
Dicotyledon plantlet
castor oil plant showing its prominent two embryonic leaves (cotyledons
), which differ from the adult leaves

The dicotyledons, also known as dicots (or, more rarely, dicotyls),[2] are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, that the seed has two embryonic leaves or cotyledons. There are around 200,000 species within this group.[3] The other group of flowering plants were called monocotyledons (or monocots), typically each having one cotyledon. Historically, these two groups formed the two divisions of the flowering plants.

Largely from the 1990s onwards, molecular phylogenetic research confirmed what had already been suspected: that dicotyledons are not a group made up of all the descendants of a common ancestor (i.e., they are not a monophyletic group). Rather, a number of lineages, such as the magnoliids and groups now collectively known as the basal angiosperms, diverged earlier than the monocots did; in other words, monocots evolved from within the dicots, as traditionally defined. The traditional dicots are thus a paraphyletic group.[4]

The

monosulcate pollen (or derived forms): grains with a single sulcus. Contrastingly, eudicots have tricolpate
pollen (or derived forms): grains with three or more pores set in furrows called colpi.

Comparison with monocotyledons

Aside from

vascular bundles, trimerous flowers, and non-tricolpate pollen.[5] In addition, some monocots have dicot characteristics such as reticulated leaf veins.[5]

Feature In monocots In dicots
Number of parts of each flower In threes (flowers are trimerous) In fours or fives (tetramerous or pentamerous)
Number of furrows or pores in pollen One Three
Number of cotyledons (leaves in the seed) One Two
Arrangement of vascular bundles in the stem Scattered In concentric circles
Roots Are
adventitious
 Develop from the radicle
Arrangement of major leaf veins Parallel Reticulate
Secondary growth Absent Often present
Stomata
 Present on both the upper and lower epidermis of leaves More common on the lower epidermis of leaves
Comparison of monocots and dicots
Illustrations of differences between monocots and dicots

Classification

Phylogeny

The consensus phylogenetic tree used in the APG IV system shows that the group traditionally treated as the dicots is paraphyletic to the monocots:[6][7]

angiosperms

Amborellales

Nymphaeales

Austrobaileyales

core angiosperms

Chloranthales

magnoliids

Ceratophyllales
 

eudicots

monocots

 traditional dicots

Historical

Traditionally, the dicots have been called the Dicotyledones (or Dicotyledoneae), at any rank. If treated as a class, as they are within the

paraphyletic class, called Magnoliopsida, or further divided. Some botanists prefer to retain the dicotyledons as a valid class, arguing its practicality and that it makes evolutionary sense.[8]

APG vs. Cronquist

The following lists show the orders in the Angiosperm Phylogeny Group APG IV system traditionally called dicots,[7] together with the older Cronquist system.

APG IV
(paraphyletic) 		Cronquist system
(classis Magnoliopsida)
Magnoliidae (mostly basal dicots)
Hamamelidae
Caryophyllidae
Dilleniidae
Rosidae
Asteridae

Dahlgren and Thorne systems

Under the Dahlgren and Thorne systems, the

subclass
name Magnoliidae was used for the dicotyledons. This is also the case in some of the systems derived from the Cronquist system. These two systems are contrasted in the table below in terms of how each categorises by superorder; note that the sequence within each system has been altered in order to pair corresponding taxa

The

Thorne system (1992) as depicted by Reveal
is:

Dahlgren system Thorne system
Magnolianae

Ranunculanae
Magnolianae

Rafflesianae

Nymphaeanae
Nymphaeanae
Caryophyllanae
Caryophyllanae
Theanae

Plumbaginanae

Polygonanae

Primulanae

Ericanae

Theanae
Malvanae
Malvanae
Violanae
Violanae
Rosanae
Rosanae
Proteanae
Proteanae
Myrtanae
Myrtanae
Rutanae
Rutanae

Celastranae
Geranianae

Santalanae
Santalanae
Balanophoranae
Santalanae
Asteranae
Asteranae
Solananae
Solananae
Cornanae

Vitanae

Cornanae

Aralianae

Loasanae
Loasanae
Gentiananae

Lamianae
Gentiananae

There exist variances between the superorders circumscribed from each system. Namely, although the systems share common names for many of the listed superorders, the specific list orders classified within each varies. For example, Thorne's Theanae corresponds to five distinct superorders under Dahlgren's system, only one of which is called Theanae.

See also

References

  1. JSTOR 1216134
  2. ^ "Dicotyl", The Free Dictionary, retrieved 2 January 2016
  3. ISBN 978-1-84407-083-1
  4. ISBN 978-0-0805-1404-8
  5. ^ a b Monocots versus Dicots, University of California Museum of Paleontology, retrieved 25 January 2012
  6. ^ Cole, Theodor C.H.; Hilger, Hartmut H. & Stevens, Peter F. (2017), Angiosperm Phylogeny Poster - Flowering Plant Systematics (PDF), archived from the original (PDF) on 2017-05-17, retrieved 2017-07-13
  7. ^
    doi:10.1111/boj.12385
  8. doi:10.1002/tax.593001
Wikispecies has information related to Magnoliopsida.

External links

Wikispecies has information related to Magnoliopsida.
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