Information AboutDicotyledon |
|
Dicotyledons or '''"dicots"''' are a group of Flowering Plant s whose Seed typically contains two embryonic leaves or Cotyledon s. Flowering plants that are not dicotyledons are Monocotyledon s, often having one embryonic leaf only. It is now accepted, thanks to the Angiosperm Phylogeny Group (APG), 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. Morphology, compared to monocotyledons School textbooks list the differences between Monocotyledons and dicotyledons as follows. This is only a broad sketch, not to be taken literally, as there are many exceptions. The differences indicated are more true for Monocots versus Eudicots , as per the APG II System : 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 Bundle s in the 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 , 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 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 System being used: Dicotyledons according to de Candolle
Dicotyledons according to the Bentham & Hooker system The Bentham & Hooker System was an influential nineteenth century system, which treated the dicots:
Dicotyledons according to the Wettstein system An early twentieth century system, the Wettstein System treated the dicots as:
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 '').
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 '' (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 '').
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):
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 Clade s. The main clades in the APG II System :
Number of species There is no close agreement on the number of dicot species. One estimate assumes 199,350 Species within this group {Link without Title} . |