Everything About Wood: DICOTYLEDON

Friday, 8 July 2016

DICOTYLEDON

Dicot" redirects here. For the band, see Dicot (band).

The dicotyledons, also known as dicots (or more rarely dicotyls^[2]), were one of the two groups into which all the flowering plants or 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 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, namely 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 magnoliidsand groups now collectively known as the basal angiosperms, diverged earlier than the monocots did. The traditional dicots are thus a paraphyleticgroup. The largest clade of the dicotyledons are known as the eudicots. They are 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.

Dicotyledon

Lamium album (white dead nettle)

Scientific classification

Kingdom:	Plantae
(unranked)	Angiosperms

Included groups

Excluded groups

Monocot

Synonyms

Dicotyledoneae
Magnoliatae Takht.^[1]

dicotyledon plant-let

Young castor oil plant showing its prominent two embryonic leaves (cotyledons), that differ from the adult leaves.

Comparison with monocotyledons

Aside from cotyledon number, other broad differences have been noted between monocotsand dicots, although these have proven to be differences primarily between monocots and eudicots. Many early-diverging dicot groups have "monocot" characteristics such as scattered vascular bundles, trimerous flowers, and non-tricolpate pollen.^[4] In addition, some monocots have dicot characteristics such as reticulated leaf veins.^[4]

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

Classification

Historical

Traditionally the dicots have been called the Dicotyledones (or Dicotyledoneae), at any rank. If treated as a class, as in the Cronquist system, they could be called the Magnoliopsida after the type genus Magnolia. In some schemes, the eudicots were treated as a separate class, the Rosopsida (type genus Rosa), or as several separate classes. The remaining dicots (palaeodicots or basal angiosperms) may be kept in a single 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.^[5]

APG (Angiosperm Phylogeny Group) vs. Cronquist ClassificationEdit

The following lists show the orders in the APG III system traditionally called dicots,^[6]together with the older Cronquist system.

APG III (polyphyletic)	Cronquist system (classis Magnoliopsida)
Amborellales Nymphaeales Austrobaileyales Chloranthales magnoliids Canellales Laurales Magnoliales Piperales eudicots Sabiaceae Buxales Proteales Ranunculales Trochodendrales core eudicots Dilleniaceae Gunnerales Saxifragales Berberidopsidales Caryophyllales Santalales rosids Vitales fabids (eurosids I) Celastrales Cucurbitales Fabales Fagales Malpighiales Oxalidales Rosales Zygophyllales malvids (eurosids II) Brassicales Crossosomatales Geraniales Huerteales Malvales Myrtales Picramniales Sapindales asterids Cornales Ericales lamiids (euasterids I) Boraginaceae Vahliaceae Icacinaceae Metteniusaceae Oncothecaceae Garryales Gentianales Lamiales Solanales campanulids (euasterids II) Apiales Aquifoliales Asterales Bruniales Dipsacales Escalloniales Paracryphiales	Magnoliidae (mostly basal dicots) Magnoliales Laurales Piperales Aristolochiales Illiciales Nymphaeales Ranunculales Papaverales Hamamelidae Trochodendrales Hamamelidales Daphniphyllales Didymelales Eucommiales Urticales Leitneriales Juglandales Myricales Fagales 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 Linales Polygalales Sapindales Geraniales Apiales Asteridae Gentianales Solanales Lamiales Callitrichales Plantaginales Scrophulariales Campanulales Rubiales Dipsacales Calycerales Asterales