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Dicotyledon
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Image:Young castor bean plant showing prominent cotyledons.jpg castor oil plant.html" title="Meaning of right right|thumb|200px|Young [[castor oil plant showing its prominent two embryonic leaves (
cotyledons), that differ from the adult leaves.html" title="Meaning of thumb|200px|Young [[castor oil plant">right|thumb|200px|Young [[castor oil plant showing its prominent two embryonic leaves (
cotyledons), that differ from the adult leaves">thumb|200px|Young [[castor oil plant">right|thumb|200px|Young [[castor oil plant showing its prominent two embryonic leaves (
cotyledons), that differ from the adult leaves
'''Dicotyledons''' or '''"dicots"''' is a name for a group of
flowering plants whose
seed typically contains two embryonic leaves or
cotyledons. Flowering plants that are not dicotyledons are
monocotyledons, often having one embryonic leaf only.
It is now accepted, thanks to the
Angiosperm Phylogeny Group, that monocotyledons evolved from within the dicotyledons, and as such the latter form a
paraphyletic group. This means that dicotyledons no longer are regarded as a "good" group, and the names "dicotyledons" and "dicots" are no longer to be used, at least in a taxonomic sense. The vast majority of the former dicots, 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.
image:Magnolia_Watsoni.JPG thumb|right|200px|An example of a trimerous and non-eudicot flower: ''Magnolia''
Morphology, compared to monocotyledons
The schoolbooks list the differences between
monocotyledons and dicotyledons as follows. Oviously this is a broad sketch only, not to be taken literally. There are many exceptions. The differences indicated are more true for
monocots versus
eudicots, as per
APG II system APG:
'''Flowers:''' In monocots, flowers are trimerous (number of flower parts in a whorl in threes) while in dicots the flowers are tetramerous or pentamerous (flower parts are in fours or fives).
'''Pollen:''' In monocots, pollen has one
furrow or
pore while in dicots they have three.
'''Seeds:''' In monocots, the embryo has one
cotyledon while the embryo of the dicot has two.
'''Stems:''' In monocots,
vascular bundles in the
Plant stem stem are scattered, in dicots arranged in a ring.
'''Roots:''' In monocots, roots are
adventitious, while in dicots they develop from the
radicle.
'''Leaves:''' In monocots, the major leaf
veins are
Parallel (geometry) parallel, while in dicots they are reticulate.
Taxonomy
The dicots were recognised as a separate group by
John Ray, so they predate
Carolus Linnaeus (see also the
history of plant systematics. The traditional name for this group has long been ''Dicotyledones'', a
descriptive botanical names descriptive botanical name that may be used at any rank. Early users, such as
A.P. de Candolle preferred the spelling ''Dicotyledoneae''. The taxonomy of the plants belonging to this group vary with the
List of systems of plant taxonomy system being used:
Dicotyledons according to de Candolle
* ''
Dicotyledoneae''
*: ''
Thalamiflorae''
*: ''
Calyciflorae''
*: ''
Corolliflorae''
*: ''
Monochlamydeae''
Dicotyledons according to the Bentham & Hooker system
The
Bentham & Hooker system was an influential nineteenth century system, which treated the dicots:
*''Dicotedonum polypetalarum''
*: ''
Thalamiflorae''
*: ''
Disciflorae''
*: ''
Calyciflorae''
*''Dicotyledones
gamopetalae''
*: ''
Inferae''
*: ''
Heteromerae''
*: ''
Bicarpellatae''
*''Dicotedones
monochlamideae''
Dicotyledons according to the Wettstein system
An early twenthieth century system, the
Wettstein system treated the dicots as:
* 1. classis ''Dicotyledones''
*: 1. subclassis ''
Choripetalae''
*:: A. ''
Monochlamideae''
*:: B. ''
Dialypetalae''
*: 2. subclassis ''
Sympetalae''
Dicotyledons according to Cronquist
In the
Cronquist system, it was treated as class ''
Magnoliopsida'', a name formed from the family name ''
Magnoliaceae'' (Art 16 ''
ICBN'').
{{Wikispecies|Magnoliopsida}}
* class ''
Magnoliopsida''
*: subclass ''
Magnoliidae''
*: subclass ''
Hamamelidae''
*: subclass ''
Caryophyllidae''
*: subclass ''
Dilleniidae''
*: subclass ''
Rosidae''
*: subclass ''
Asteridae''
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 dicotyledons are treated at the rank of subclass, named ''
Magnoliidae'' (as in [http://www.bioimages.org.uk/HTML/T79.HTM this example]). In that case the name ''Magnoliopsida'' (at the rank of class) refers to the
flowering plants (the angiosperms).
Dicotyledons according to Dahlgren
In the
Dahlgren system, it was treated as subclass ''
Magnoliidae'', a name formed from the family name ''
Magnoliaceae'' (Art 16 ''
ICBN'').
*: subclass ''
Magnoliidae''
*:: superorder ''
Magnolianae''
*:: superorder ''
Nymphaeanae''
*:: superorder ''
Ranunculanae''
*:: superorder ''
Caryophyllanae''
*:: superorder ''
Polygonanae''
*:: superorder ''
Plumbaginanae''
*:: superorder ''
Malvanae''
*:: superorder ''
Violanae''
*:: superorder ''
Theanae''
*:: superorder ''
Primulanae''
*:: superorder ''
Rosanae''
*:: superorder ''
Proteanae''
*:: superorder ''
Myrtanae''
*:: superorder ''
Rutanae''
*:: superorder ''
Vitanae''
*:: superorder ''
Santalanae''
*:: superorder ''
Balanophoranae''
*:: superorder ''
Aralianae''
*:: superorder ''
Asteranae''
*:: superorder ''
Solananae''
*:: superorder ''
Ericanae''
*:: superorder ''
Cornanae''
*:: superorder ''
Loasanae''
*:: superorder ''
Gentiananae''
*:: superorder ''
Lamianae''
Dicotyledons according to Thorne (1992)
In the
Thorne system (1992), it was treated as subclass ''
Magnoliidae'', a name formed from the family name ''
Magnoliaceae'' (Art 16 ''
ICBN''). The internal taxonomy in the
Thorne system (in the version of the system as depicted by Reveal):
*: subclass ''Magnoliidae'' [= dicotyledons ]
*:: superorder ''
Magnolianae''
*:: superorder ''
Nymphaeanae''
*:: superorder ''
Rafflesianae''
*:: superorder ''
Caryophyllanae''
*:: superorder ''
Theanae''
*:: superorder ''
Celastranae''
*:: superorder ''
Malvanae''
*:: superorder ''
Violanae''
*:: superorder ''
Santalanae''
*:: superorder ''
Geranianae''
*:: superorder ''
Rutanae''
*:: superorder ''
Proteanae''
*:: superorder ''
Rosanae''
*:: superorder ''
Cornanae''
*:: superorder ''
Asteranae''
*:: superorder ''
Solananae''
*:: superorder ''
Loasanae''
*:: superorder ''
Myrtanae''
*:: superorder ''
Gentiananae''
According to APG II
As noted above, the APG emphatically reject the the dicots as a natural group, and in effect the plants belonging to the "dicots" are a
paraphyletic gathering of all angiosperms except the monocots. The
Angiosperm Phylogeny Group does not use ranks above the level of order and uses informal names for
clades. The main clades in the
APG II system:
*'''angiosperms :'''
*:'''
magnoliids'''
*:'''
monocots'''
*::'''
commelinids'''
*:'''
eudicots'''
*::'''
core eudicots'''
*:::'''
rosids'''
*::::'''
eurosids I'''
*::::'''
eurosids II'''
*:::'''
asterids'''
*::::'''
euasterids I'''
*::::'''
euasterids II'''
Number of species
There is no close agreement on the number of dicot species. One estimate assumes 199,350
species within this group [http://www.redlist.org/info/tables/table1].
Category:Magnoliopsida
category: plant taxonomy
bg:ДвуÑ?емеделни
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pl:Dwuliścienne
pt:Dicotiledónea
ru:Двудольные
sr:Дикотиледон
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{{categoryredirect|Magnoliopsida}}
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