Theeudicots oreudicotyledons areflowering plants that have twoseed leaves (cotyledons) upongermination.[1] The term derives fromdicotyledon (etymologically,eu = true;di = two;cotyledon = seed leaf). Historically, authors have used the termstricolpates ornon-magnoliid dicots. The current botanical terms were introduced in 1991, byevolutionary botanist James A. Doyle andpaleobotanist Carol L. Hotton, to emphasize the later evolutionarydivergence of tricolpatedicots from earlier, less specialized, dicots.[2]
The close relationships among flowering plants withtricolpate pollen grains was initially seen in morphological studies ofshared derived characters. These plants have a distinct trait in their pollen grains of exhibiting three colpi or grooves paralleling the polar axis.[3]
Latermolecular evidence confirmed the genetic basis for the evolutionary relationships among flowering plants with tricolpate pollen grains and dicotyledonous traits. The term means "true dicotyledons", as it contains the majority of plants that have been considered dicots and havecharacteristics of the dicots. One of the genetic traits which defines the eudicots is theduplication ofDELLA protein-encoding genes in theirmost recent common ancestor.[4] The term "eudicots" has subsequently been widely adopted inbotany to refer to one of the two largest clades ofangiosperms (constituting over 70% of the angiosperm species),monocots being the other. The remaining angiosperms includemagnoliids and what are sometimes referred to asbasal angiosperms or paleodicots, but these terms have not been widely or consistently adopted, as they do not refer to amonophyletic group.[citation needed]
According tomolecular clock calculations, the lineage that led to eudicots split from other plants about 134million years ago[5] or 155–160 million years ago.[6]
The earlier name for the eudicots istricolpates, a name which refers to the grooved structure of thepollen. Members of the group have tricolpate pollen, or forms derived from it. These pollens have three or more pores set in furrows called colpi. In contrast, most of the otherseed plants (that is thegymnosperms, the monocots and the paleodicots) produce monosulcate pollen, with a single pore set in a differently oriented groove called the sulcus. The name "tricolpates" is preferred by some botanists to avoid confusion with the dicots, a nonmonophyletic group.[7]
The name "eudicots" (plural) is used in theAPG systems (fromAPG system, of 1998, toAPG IV system, of 2016) for classification of angiosperms. It is applied to aclade, a monophyletic group, which includes most of the (former) dicots.[citation needed]
"Tricolpate" is a synonym for the "Eudicot"monophyletic group, the "truedicotyledons" (which are distinguished from all other flowering plants by theirtricolpatepollen structure). The number ofpollen grainfurrows orpores helps classify theflowering plants, with eudicots having threecolpi (tricolpate), and other groups having onesulcus.[8][7]
Pollenapertures are any modification of the wall of the pollen grain. These modifications include thinning, ridges and pores, they serve as an exit for the pollen contents and allow shrinking and swelling of the grain caused by changes in moisture content. The elongated apertures/ furrows in the pollen grain are calledcolpi (singularcolpus), which, along with pores, are a chief criterion for identifying the pollen classes.[9]
The eudicots can be divided into two groups: the basal eudicots and thecore eudicots.[10] Basal eudicot is an informal name for aparaphyletic group. The core eudicots are a monophyletic group.[11] A 2010 study suggested the core eudicots can be divided into two clades,Gunnerales and a clade calledPentapetalae, comprising all the remaining core eudicots.[12]
The Pentapetalae can be then divided into three clades:[citation needed]
^Magallon, S; Gomez-Acevedo, S; Sanchez-Reyes, LL; Tania Hernandez-Hernandez, T (2015). "A metacalibrated time-tree documents the early rise of flowering plant phylogenetic diversity".New Phytologist.207:437–453.doi:10.1111/nph.13264.
^Based on: Stevens, P.F. (2001–2014)."Trees".Angiosperm Phylogeny Website. Retrieved2014-11-17. Stevens, P.F. (2001–2016)."Eudicots".Angiosperm Phylogeny Website. Retrieved2014-11-17.
Doyle, J.A.; Hotton, C.L. (1991). "Diversification of earlyangiosperm pollen in a cladistic context". In Blackmore, S.; Barnes, S.H. (eds.).Pollen and Spores. Patterns of Diversification. Systematics Association Publications. Vol. 44. Clarendon Press. pp. 169–195.ISBN9780198577461.
