Editing Monocotyledon (section)

==Taxonomy==

===Early history===

==== Pre-Linnean ====
[[File:Ray-Malpighi cotyledon.jpg|thumb|Illustrations of [[cotyledons]] by [[John Ray]] 1682, after [[Marcello Malpighi|Malpighi]]]]
Monocots were first recognized as a group in [[Matthias de l'Obel]]'s [[Matthias de l'Obel#Stirpium adversaria nova (1570-71)|''Stirpium adversaria nova'']]. Searching for non-pharmacological characteristics to classify plants by, he chose on [[leaf]] form and [[Leaf#Venation|venation]], and observed that the majority of plants had broad leaves with net-like venation, but some had long and straight leaves with parallel veins.<ref name=ObelStirp65/> He did not decide on any formal name for the two groups he discovered, and his new classification scheme did not receive much appraisal and only saw moderate success within academic circles.{{sfn|Vines|1913|loc=p.&nbsp;10}}{{sfn|Hoeniger|Hoeniger|1969}}<ref name=pavordN.339/><ref>{{cite journal |last1=Houtzager |first1=HL |date=27 November 1976 |title=Matthias Lobelius, 16e eeuwse kruidkundige en geneesheer |trans-title=Mathias Lobelius, 16th century herbalist and physician |url=https://www.ntvg.nl/system/files/publications/1976121100001a.pdf |journal=[[Nederlands Tijdschrift voor Geneeskunde]] |language=nl |volume=120 |issue=4– |pages=2110–3 |pmid=796733}}</ref>

Formal description dates from [[John Ray]]'s studies of [[seed]] structure in the 17th century. Ray, who is often considered the first botanical [[systematist]],{{sfn|Pavord|2005}} observed the [[dichotomy]] of [[cotyledon]] structure in his examination of seeds. He reported his findings in a paper read to the [[Royal Society]] on 17 December 1674, entitled "A Discourse on the Seeds of Plants".{{sfn|Chase|2004}}
{{Quotebox|title=''A Discourse on the Seeds of Plants''|align=center| salign=right|quote= <poem>The greatest number of plants that come of seed spring at first out of the earth with two leaves which being for the most part of a different figure from the succeeding leaves are by our gardeners not improperly called the seed leaves...  <br/>In the first kind the seed leaves are nothing but the two lobes of the seed having their plain sides clapt together like the two halves of a walnut and therefore are of the just figure of the seed slit in sunder flat wise...<br/>Of seeds that spring out of the earth with leaves like the succeeding and no seed leaves I have observed two sorts. 1. Such as are congenerous to the first kind precedent that is whose pulp is divided into two lobes and a radicle... <br/>2. Such which neither spring out of the ground with seed leaves nor have their pulp divided into lobes </poem>|source= John Ray (1674), pp.&nbsp;164, 166{{sfn|Ray|1674|loc=[https://books.google.com/books?id=o2EVAAAAQAAJ&pg=PA164 pp.&nbsp;164, 166]}}}} Since this paper appeared a year before the publication of [[Malpighi]]'s ''Anatome Plantarum'' (1675–1679), Ray has the priority. At the time, Ray did not fully realise the importance of his discovery{{sfn|Raven|1950}} but progressively developed this over successive publications. And since these were in Latin, "seed leaves" became ''folia seminalia''{{sfn|Ray|1682|loc=[https://www.biodiversitylibrary.org/item/84226#page/35/mode/1up ''De foliis plantarum seminalibus dictis'' p.&nbsp;7]}} and then ''cotyledon'', following [[Malpighi]].{{sfn|Short|George|2013|loc=[https://books.google.com/books?id=dFcKLxqEAj4C&pg=PA15 p.&nbsp;15]}}{{sfn|Ray|1682|loc=[https://archive.org/stream/methodusplantaru00rayj#page/12/mode/2up ''De plantula seminali reliquisque femine contentis'' p.&nbsp;13]}} Malpighi and Ray were familiar with each other's work,{{sfn|Raven|1950}} and Malpighi in describing the same structures had introduced the term cotyledon,{{sfn|Malpighi|1679|loc=[https://books.google.com/books?id=nSEOAAAAQAAJ&pg=PA18 ''De seminum vegetatione'' p.&nbsp;18]}} which Ray adopted in his subsequent writing.
{{Quotebox|title=''De seminum vegetatione''|align=center| salign=right|quote= <poem>''Mense quoque Maii, alias seminales plantulas Fabarum, & Phaseolorum, ablatis pariter binis seminalibus foliis, seu cotyledonibus, incubandas posui''<br/>In the month of May, also, I incubated two seed plants, [[Vicia faba|Faba]] and [[Phaseolus]], after removing the two seed leaves, or cotyledons</poem>|source= Marcello Malpighi (1679), p.&nbsp;18{{sfn|Malpighi|1679|loc=[https://books.google.com/books?id=nSEOAAAAQAAJ&pg=PA18 ''De seminum vegetatione'' p.&nbsp;18]}}}} In this experiment, Malpighi also showed that the cotyledons were critical to the development of the plant, proof that Ray required for his theory.{{sfn|Bewley|Black|Halmer|2006|loc=[https://books.google.com/books?id=aE414KuXu4gC&pg=PA334 History of seed research p.&nbsp;334]}} In his ''Methodus plantarum nova''{{sfn|Ray|1682}} Ray also developed and justified the "natural" or pre-evolutionary approach to classification, based on characteristics selected ''[[a posteriori]]'' in order to group together taxa that have the greatest number of shared characteristics. This approach, also referred to as polythetic would last till [[evolutionary theory]] enabled [[Eichler system|Eichler]] to develop the [[phyletic]] system that superseded it in the late nineteenth century, based on an understanding of the acquisition of characteristics.{{sfn|Stuessy|2009|loc=[https://books.google.com/books?id=b9Q2EOkw7toC&pg=PA47 Natural classification p.&nbsp;47]}}{{sfn|Datta|1988|loc=[https://books.google.com/books?id=X7lfMACvjs4C&pg=PA21 Systems of classification p.&nbsp;21]}}{{sfn|Stace|1989|loc=[https://books.google.com/books?id=VfQnuwh3bw8C&pg=PA19 The development of plant taxonomy p.&nbsp;17]}} He also made the crucial observation ''Ex hac seminum divisione sumum potest generalis plantarum distinctio, eaque meo judicio omnium prima et longe optima, in eas sci. quae plantula seminali sunt bifolia aut διλόβω, et quae plantula sem. adulta analoga.'' (From this division of the seeds derives a general distinction amongst plants, that in my judgement is first and by far the best, into those seed plants which are bifoliate, or bilobed, and those that are analogous to the adult), that is between monocots and dicots.{{sfn|Raven|1950|loc=[https://books.google.com/books?id=ETusSTe5O8YC&pg=PA195 p.&nbsp;195]}}{{sfn|Bewley|Black|Halmer|2006|loc=[https://books.google.com/books?id=aE414KuXu4gC&pg=PA334 History of seed research p.&nbsp;334]}} He illustrated this by quoting from Malpighi and including reproductions of Malpighi's drawings of cotyledons (see figure).{{sfn|Ray|1682|loc=[https://archive.org/stream/methodusplantaru00rayj#page/n39/mode/2up ''De foliis plantarum seminalibus dictis'' p.&nbsp;11]}} Initially Ray did not develop a classification of flowering plants (florifera) based on a division by the number of cotyledons, but developed his ideas over successive publications,{{sfn|Ray|1696}} coining the terms ''Monocotyledones'' and ''Dicotyledones'' in 1703,{{sfn|Ray|1703|loc=[https://archive.org/stream/joannisrajisocie00rayj#page/n39/mode/2up pp.&nbsp;1–2]}} in the revised version of his ''Methodus'' (''Methodus plantarum emendata''), as a primary method for dividing them, ''Herbae floriferae, dividi possunt, ut diximus, in Monocotyledones & Dicotyledones'' (Flowering plants, can be divided, as we have said, into Monocotyledons & Dicotyledons).{{sfn|Ray|1703|loc=[https://archive.org/stream/joannisrajisocie00rayj#page/16/mode/2up p.&nbsp;16]}}

==== Post Linnean ====

Although [[Carl Linnaeus|Linnaeus]] (1707–1778) did not utilise Ray's discovery, basing his own classification solely on [[floral reproductive morphology]], the term was used shortly after his classification appeared (1753) by [[Scopoli]] and who is credited for its introduction.{{efn|Scopoli, in his treatment of Linnaeus' scheme comments in the ''Hexandria polygynia'' on the fact that ''[[Alisma]]'' is a member of the ''Gens monocotyledon''<ref name=ScopoliAlisma/>}} Every [[taxonomist]] since then, starting with [[Antoine Laurent de Jussieu|De Jussieu]] and [[Augustin De Candolle|De Candolle]], has used Ray's distinction as a major classification characteristic.{{efn|See also [[John Lindley|Lindley]]'s review of classification systems up to 1853,{{sfn|Lindley|1853}} and [[Rolf Dahlgren|Dahlgren]]'s from 1853–1982{{sfn|Dahlgren|Clifford|1982}}}}<ref name=Kubitzmmonohist/> In [[De Jussieu system|De Jussieu's system]] (1789), he followed Ray, arranging his Monocotyledones into three classes based on stamen position and placing them between [[Acotyledones]] and Dicotyledones.{{sfn|Jussieu|1789}} [[De Candolle system|De Candolle's system]] (1813) which was to predominate thinking through much of the 19th century used a similar general arrangement, with two subgroups of his ''Monocotylédonés'' (Monocotyledoneae).{{sfn|de Candolle|1819}} [[John Lindley|Lindley]] (1830) followed De Candolle in using the terms Monocotyledon and Endogenae{{efn|''Endogènes'' (ενδον within + γεναω I create)}} interchangeably. They considered the monocotyledons to be a group of  [[vascular plants]] (''Vasculares'') whose vascular bundles were thought to arise from within (''Endogènes'' or [[endogenous]]).{{sfn|Lindley|1830}}

Monocotyledons remained in a similar position as a major division of the flowering plants throughout the nineteenth century, with minor variations. [[George Bentham]] and [[Joseph Dalton Hooker|Hooker]] (1862–1883) used Monocotyledones, as would [[Richard Wettstein|Wettstein]],{{sfn|Wettstein|1924}} while [[August Eichler]] used Mononocotyleae{{sfn|Eichler|1886}} and [[Adolf Engler|Engler]], following de Candolle, Monocotyledoneae.{{sfn|Engler|1886}} In the twentieth century, some authors used alternative names such as [[Charles Bessey|Bessey]]'s (1915) Alternifoliae{{sfn|Bessey|1915}} and [[Arthur Cronquist|Cronquist]]'s (1966) Liliatae.{{sfn|Cronquist|Takhtajan|Zimmermann|1966}} Later (1981) Cronquist changed Liliatae to Liliopsida,{{sfn|Cronquist|1981}} usages also adopted by [[Takhtajan]] simultaneously.<ref name=TakhtajanLiliops/>  [[Robert F. Thorne|Thorne]] (1992){{sfn|Thorne|1992a}} and [[Rolf|Dahlgren]] (1985){{sfn|Dahlgren|Clifford|Yeo|1985}} also used Liliidae as a synonym.

Taxonomists had considerable latitude in naming this group, as the Monocotyledons were a group above the rank of family. Article 16 of the ''[[ICBN]]'' allows either a [[descriptive botanical name]] or a name formed from the name of an included family.

In summary they have been variously named, as follows:
* class Monocotyledoneae in the [[de Candolle system]] and the [[Engler system]]
* class Monocotyledones in the [[Bentham & Hooker system]] and the [[Wettstein system]]
* class Monocotyleae in the [[Eichler system]]
* class Liliatae then [[Liliopsida]] in the [[Takhtajan system]] and the [[Cronquist system]]
* subclass [[Liliidae]] in the [[Dahlgren system]] and the [[Thorne system (1992)|Thorne system]]

=== Modern era ===

Over the 1980s, a more general review of the classification of [[angiosperms]] was undertaken. The 1990s saw considerable progress in plant [[phylogenetics]] and [[cladistic]] theory, initially based on ''[[rbcL]]'' gene sequencing and cladistic analysis, enabling a [[phylogenetic tree]] to be constructed for the flowering plants.{{sfn|Chase et al|1993}} The establishment of major new [[clades]] necessitated a departure from the older but widely used classifications such as Cronquist and Thorne, based largely on morphology rather than genetic data. These developments complicated discussions on [[plant evolution]] and necessitated a major taxonomic restructuring.{{sfn|APG|1998}}{{sfn|APG III|2009}}

This [[DNA]] based [[molecular phylogenetic]] research confirmed on the one hand that the monocots remained as a well defined [[monophyly|monophyletic]] group or [[clade]], in contrast to the other historical divisions of the flowering plants, which had to be substantially reorganized.{{sfn|Chase|2004}} No longer could the angiosperms be simply divided into monocotyledons and dicotyledons; it was apparent that the monocotyledons were but one of a relatively large number of defined groups within the angiosperms.{{sfn|Bremer|Wanntorp|1978}} Correlation with morphological criteria showed that the defining feature was not cotyledon number but the separation of angiosperms into two major [[pollen]] types, [[uniaperturate]] ([[monosulcate]] and monosulcate-derived) and triaperturate (tricolpate and tricolpate-derived), with the monocots situated within the uniaperturate groups.{{sfn|Chase et al|1993}} The formal taxonomic ranking of Monoctyledons thus became replaced with monocots as an informal clade.{{sfn|Chase|Stevenson|Wilkin|Rudall|1995b}}{{sfn|Chase|2004}} This is the name that has been most commonly used since the publication of the [[Angiosperm Phylogeny Group]] [[APG system|(APG) system]] in 1998 and regularly updated since.{{sfn|APG|1998}}{{sfn|APG II|2003}}{{sfn|APG III|2009}}{{sfn|LAPGIII|2009}}{{sfn|Chase|Reveal|2009}}{{sfn|APG IV|2016}}

Within the angiosperms, there are two major [[evolutionary grade|grade]]s, a small early branching [[basal (phylogenetics)|basal]] grade, the [[basal angiosperms]] (ANA grade) with three [[lineage (evolution)|lineages]] and a larger late branching grade, the [[core angiosperms]] (mesangiosperms) with five lineages, as shown in the [[cladogram]].

{|
|{{anchor|Clad1}}'''Cladogram I: Phylogenetic position of the monocots within the angiosperms in APG IV (2016)'''{{sfn|APG IV|2016}}
{{barlabel
|size=8
|at1=2|bar1=green|label1=basal angiosperms
|at2=6|bar2=purple|label2=core angiosperms
|cladogram=
{{clade|style=font-size:100%;line-height:100%

|label1=[[angiosperms]]
|1={{clade
  |1=[[Amborellales]]|barbegin1=green
  |2={{clade
    |1=[[Nymphaeales]]|bar1=green
    |2={{clade
      |1=[[Austrobaileyales]]|barend1=green
      |label2=
      |2={{clade
        |1={{clade
          |1=[[magnoliids]]|barbegin1=purple
          |2=[[Chloranthales]]|bar2=purple
           }}
        |2={{clade
          |1='''monocots'''|bar1=purple
          |2={{clade
            |1=[[Ceratophyllales]]|bar1=purple
            |2=[[eudicots]]|barend2=purple
             }}
           }}
         }}
       }}
     }}
   }}
}}
}}
|}

=== Subdivision===

While the monocotyledons have remained extremely stable in their outer borders as a well-defined and coherent monophylectic group, the deeper internal relationships have undergone considerable flux, with many competing classification systems over time.<ref name=Kubitzmmonohist/>

Historically, [[George Bentham|Bentham]] (1877), considered the monocots to consist of four [[alliance (taxonomy)|alliances]], Epigynae, Coronariae, Nudiflorae and Glumales, based on floral characteristics. He describes the attempts to subdivide the group since the days of [[John Lindley|Lindley]] as largely unsuccessful.{{sfn|Bentham|1877}} Like most subsequent classification systems it failed to distinguish between two major orders, [[Liliales]] and [[Asparagales]], now recognised as quite separate.{{sfn|Fay|2013}} A major advance in this respect was the work of [[Rolf Dahlgren]] (1980),{{sfn|Dahlgren|1980}} which would form the basis of the [[Angiosperm Phylogeny Group]]'s (APG) subsequent modern classification of monocot families. Dahlgren who used the alternate name [[Lilliidae]] considered the monocots as a [[Subclass (biology)|subclass]] of [[angiosperms]] characterised by a single cotyledon and the presence of triangular protein bodies in the [[sieve tube]] [[plastids]]. He divided the monocots into seven [[Order (biology)|superorders]], Alismatiflorae, Ariflorae, Triuridiflorae, [[Liliiflorae]], Zingiberiflorae, Commeliniflorae and Areciflorae. With respect to the specific issue regarding Liliales and Asparagales, Dahlgren followed [[Herbert Huber (botanist)|Huber]] (1969){{sfn|Huber|1969}} in adopting a [[Lumpers and splitters|splitter]] approach, in contrast to the longstanding tendency to view [[Liliaceae]] as a very broad [[sensu lato]] [[Family (biology)|family]]. Following Dahlgren's untimely death in 1987, his work was continued by his widow, [[Gertrud Dahlgren]], who published a revised version of the classification in 1989. In this scheme the [[suffix]] ''-florae'' was replaced with ''-anae'' (''e.g.'' [[Alismatanae]]) and the number of superorders expanded to ten with the addition of Bromelianae, Cyclanthanae and Pandananae.{{sfn|Dahlgren|1989}}

Molecular studies have both confirmed the [[monophyly]] of the monocots and helped elucidate relationships within this group. The [[Angiosperm Phylogeny Group|APG]] system does not assign the monocots to a taxonomic rank, instead recognizing a monocots clade.{{sfn|Chase et al| 1995}}{{sfn|Chase et al|2000}}{{sfn|Davis et al|2004}}{{sfn|Soltis|Soltis|2004}} However, there has remained some uncertainty regarding the exact relationships between the major lineages, with a number of competing models (including APG).{{sfn|Zeng et al|2014}}

The APG system establishes eleven orders of monocots.{{sfn|Cantino et al|2007}}{{sfn|APG IV|2016}} These form three grades, the [[alismatid monocots]], [[lilioid monocots]] and the [[commelinid monocots]] by order of branching, from early to late. In the following [[cladogram]] numbers indicate [[crown group]] (most recent common ancestor of the sampled species of the clade of interest) divergence times in [[mya (unit)|mya]] (million years ago).{{sfn|Hertwick et al.|2015}}

{|
|{{anchor|Clad2}}'''Cladogram 2: The phylogenetic composition of the monocots'''{{sfn|APG IV|2016}}{{sfn|Givnish et al|2018}}

{{barlabel|size=12|at1=5.5|label1=[[Lilioid monocots]] |bar1=purple|at2=2|label2=[[Alismatid monocots]]|bar2=green|style=font-size:100%;line-height:125%;width:400px;|cladogram=

{{clade
|align=center
|label1='''monocots''' (131 [[myr|MYA]])
|1={{clade
    |1={{clade
       |1={{clade
       |label1=
        |1=[[Acorales]]|barbegin1=green
        |2={{clade
           |label1=
           |1=[[Alismatales]]|barend1=green
          |label2=122 MYA
          |2={{clade
            |1=[[Petrosaviales]] | barbegin1=purple
            |label1=
            |2={{clade
              |label1=120 MYA
              |1={{clade
                |1=[[Dioscoreales]] (115 MYA)| bar1=purple
                |2=[[Pandanales]] (91 MYA) | bar2=purple
                 }}
              |2={{clade 
                |1=[[Liliales]] (121 MYA)| bar1=purple
                |label2=121 MYA
                |2={{clade 
                  |1=[[Asparagales]] (120 MYA)| barend1=purple
                  |label2=[[commelinids]] (118 MYA)
                  |2={{clade
                    |label1=
                    |1=[[Arecales]]
                    |2={{clade
                      |label1=
                      |1=[[Poales]]
                      |2={{clade
                        |label1=
                        | 1= [[Zingiberales]]
                        | 2= [[Commelinales]]
                         }}
                       }}
                     }}
                   }}
                 }}
               }}
             }}
           }}
         }}
       }}
     }}
   }}
}}
|}

{{Clear}}
Of some 70,000 [[species]],<ref name=CoL/> by far the largest number (65%) are found in two [[Family (biology)|families]], the orchids and grasses. The orchids ([[Orchidaceae]], [[Asparagales]]) contain about 25,000 species and the grasses ([[Poaceae]], [[Poales]]) about 11,000. Other well known groups within the Poales [[Order (biology)|order]] include the [[Cyperaceae]] (sedges) and [[Juncaceae]] (rushes), and the monocots also include familiar families such as the palms ([[Arecaceae]], Arecales) and lilies ([[Liliaceae]], [[Liliales]]).{{sfn|Fay|2013}}{{sfn|Panis|2008}}

===Evolution===

In [[phyletic|prephyletic]] classification systems monocots were generally positioned between plants other than angiosperms and dicots, implying that monocots were more primitive. With the introduction of phyletic thinking in taxonomy (from the [[Eichler system|system of Eichler]] 1875–1878 onwards) the predominant theory of monocot origins was the ranalean (ranalian) theory, particularly in the work of [[Charles Bessey|Bessey]] (1915),{{sfn|Bessey|1915}} which traced the origin of all flowering plants to a Ranalean type, and reversed the sequence making dicots the more primitive group.<ref name=Kubitzmmonohist/>

The monocots form a [[monophyletic]] group arising early in the history of the [[flowering plant]]s, but the fossil record is meagre.{{sfn|Ganfolfo et al|1998}} The earliest fossils presumed to be monocot remains date from the [[Cretaceous|early Cretaceous]] period. For a very long time, [[fossil]]s of palm trees were believed to be the oldest monocots,{{sfn|Smith et al|2010|loc=[https://books.google.com/books?id=eC0WBAAAQBAJ&pg=PA38 p.&nbsp;38]}} first appearing 90 million years ago ([[mya (unit)|mya]]), but this estimate may not be entirely true.{{sfn|Herendeen|Crane|1995}} At least some putative monocot fossils have been found in strata as old as the eudicots.{{sfn|Herendeen|Crane|Drinnan|1995}} The oldest fossils that are unequivocally monocots are pollen from the Late [[Barremian]]–[[Aptian]] – Early [[Cretaceous]] period, about 120-110 million years ago, and are assignable to [[clade]]-[[Pothoideae]]-Monstereae Araceae; being Araceae, sister to other [[Alismatales]].{{sfn|Gandolfo|Nixon|Crepet|2002}}{{sfn|Friis|Pedersen|Crane|2004}}{{sfn|Friis|Pedersen|Crane|2006}} They have also found flower fossils of Triuridaceae (Pandanales) in Upper Cretaceous rocks in New Jersey,{{sfn|Gandolfo|Nixon|Crepet|2002}} becoming the oldest known sighting of [[saprophytic]]/[[mycotrophic]] habits in [[angiosperm]] plants and among the oldest known fossils of monocotyledons.

Topology of the angiosperm [[phylogenetic]] tree could imply that the monocots are among the oldest lineages of angiosperms, which would support the theory that they are just as old as the eudicots. The pollen of the eudicots dates back 125 million years, so the lineage of monocots should be that old too.{{sfn|Soltis et al.|2005}}

==== Molecular clock estimates  ====

[[Kåre Bremer]], using [[RuBisCO large subunit|rbcL]] sequences and the [[Network science|mean path length method]] for estimating [[genetic divergence|divergence times]], estimated the age of the monocot crown group (i.e. the time at which the ancestor of today's ''Acorus'' diverged from the rest of the group) as 134 million years.{{sfn|Bremer|2000}}{{sfn|Bremer|2002}} Similarly, Wikström ''et al.'',{{sfn|Wikström|Savolainen|Chase|2001}} using Sanderson's [[Robust statistics|non-parametric rate smoothing approach]],{{sfn|Sanderson|1997}} obtained ages of 127–141 million years for the crown group of monocots.{{sfn|Sanderson et al|2004}} All these estimates have large error ranges (usually 15-20%), and Wikström ''et al.'' used only a single calibration point,{{sfn|Wikström|Savolainen|Chase|2001}} namely the split between [[Fagales]] and [[Cucurbitales]], which was set to 84&nbsp;Ma, in the late [[Santonian]] period. Early molecular clock studies using strict clock models had estimated the monocot crown age to 200 ± 20 million years ago{{sfn|Savard et al|1994}} or 160 ± 16 million years,{{sfn|Goremykin|Hansman|Martin|1997}} while studies using relaxed clocks have obtained 135-131 million years{{sfn|Leebens-Mack et al|2005}} or 133.8 to 124 million years.{{sfn|Moore et al|2007}} Bremer's estimate of 134 million years{{sfn|Bremer|2000}} has been used as a secondary calibration point in other analyses.{{sfn|Janssen|Bremer|2004}} Some estimates place the diversification of the monocots as far back as 150&nbsp;mya in the [[Jurassic]] period.{{sfn|Zeng et al|2014}}

The lineage that led to monocots (stem group) split from other plants about 136 million years ago{{sfn|Magallon|Gomez-Acevedo|Sanchez-Reyes|Tania Hernandez-Hernandez|2015}} or 165-170 million years ago.{{sfn|Zeng et al|2014}}

====Core group====
The age of the core group of so-called 'nuclear monocots' or 'core monocots', which correspond to all orders except [[Acorales]] and Alismatales,{{sfn|Hedges|Kumar|2009|loc=[https://books.google.com/books?id=9rt1c1hl49MC&pg=PA205 p.&nbsp;205]}} is about 131 million years to present, and crown group age is about 126 million years to the present. The subsequent branching in this part of the tree (i.e. [[Petrosaviaceae]], [[Dioscoreales]] + Pandanales and [[Liliales]] clades appeared), including the crown [[Petrosaviaceae]] group may be in the period around 125–120 million years BC (about 111 million years so far{{sfn|Bremer|2000}}), and stem groups of all other orders, including [[Commelinidae]] would have diverged about or shortly after 115 million years.{{sfn|Janssen|Bremer|2004}} These and many clades within these orders may have originated in southern [[Gondwana]], i.e. Antarctica, Australasia, and southern South America.{{sfn|Bremer|Janssen|2006}}

====Aquatic monocots====
The aquatic monocots of Alismatales have commonly been regarded as "primitive".{{sfn|Hallier|1905}}{{sfn|Arber|1925}}{{sfn|Hutchinson|1973}}{{sfn|Cronquist| 1981}}{{sfn|Cronquist| 1988}}{{sfn|Takhtajan| 2009}}{{sfn|Takhtajan|1991}}{{sfn|Stebbins|1974}}{{sfn|Thorne|1976}} They have also been considered to have the most primitive foliage, which were cross-linked as Dioscoreales{{sfn|Dahlgren|Clifford|Yeo|1985}} and [[Melanthiales]].{{sfn|Thorne|1992a}}{{sfn|Thorne|1992b}} Keep in mind that the "most primitive" monocot is not necessarily "the sister of everyone else".{{sfn|Soltis et al.|2005}} This is because the ancestral or primitive characters are inferred by means of the reconstruction of character states, with the help of the phylogenetic tree. So primitive characters of monocots may be present in some derived groups. On the other hand, the basal taxa may exhibit many [[morphology (biology)|morphological]] [[autapomorphy|autapomorphies]]. So although Acoraceae is the sister group to the remaining monocotyledons, the result does not imply that Acoraceae is "the most primitive monocot" in terms of its character states. In fact, Acoraceae is highly derived in many morphological characters, and that is precisely why Acoraceae and Alismatales occupied relatively derived positions in the trees produced by Chase ''et al.''{{sfn|Chase et al| 1995}} and others.{{sfn|Loconte|Stevenson|1991}}{{sfn|Stevenson|Loconte|1995}}

Some authors support the idea of an aquatic phase as the origin of monocots.{{sfn|Henslow|1893}} The phylogenetic position of Alismatales (many water), which occupy a relationship with the rest except the Acoraceae, do not rule out the idea, because it could be 'the most primitive monocots' but not 'the most basal'. The Atactostele stem, the long and linear leaves, the absence of secondary growth (see the [[biomechanics]] of living in the water), roots in groups instead of a single root branching (related to the nature of the [[substrata (gardening)|substrate]]), including [[sympodial]] use, are consistent with a water source. However, while monocots were sisters of the aquatic [[Ceratophyllales]], or their origin is related to the adoption of some form of aquatic habit, it would not help much to the understanding of how it evolved to develop their distinctive anatomical features: the monocots seem so different from the rest of angiosperms and it's difficult to relate their morphology, anatomy and development and those of broad-leaved angiosperms.{{sfn|Zimmermann| Tomlinson| 1972}}{{sfn|Tomlinson|1995}}

====Other taxa====
In the past, taxa which had [[petiole (botany)|petiolate]] leaves with [[reticulate venation]] were considered "primitive" within the monocots, because of the superficial resemblance to the leaves of [[dicotyledons]]. Recent work suggests that while these taxa are sparse in the phylogenetic tree of monocots, such as fleshy fruited taxa (excluding taxa with aril seeds dispersed by ants), the two features would be adapted to conditions that evolved together regardless.{{sfn|Dahlgren|Clifford|1982}}{{sfn|Patterson|Givnish|2002}}{{sfn|Givnish et al.|2005}}{{sfn|Givnish et al.|2006}} Among the taxa involved were ''[[Smilax]]'', ''[[Trillium]]'' (Liliales), ''[[Dioscorea]]'' (Dioscoreales), etc. A number of these plants are [[vine]]s that tend to live in shaded habitats for at least part of their lives, and this fact may also relate to their shapeless [[stomata]].{{sfn|Cameron|Dickison|1998}} Reticulate venation seems to have appeared at least 26 times in monocots, and fleshy fruits have appeared 21 times (sometimes lost later); the two characteristics, though different, showed strong signs of a tendency to be good or bad in tandem, a phenomenon described as "concerted convergence" ("coordinated convergence").{{sfn|Givnish et al.|2005}}{{sfn|Givnish et al.|2006}}

=== Etymology ===
The name monocotyledons is derived from the traditional botanical name "Monocotyledones" or ''Monocotyledoneae'' in [[Latin]], which refers to the fact that most members of this group have one [[cotyledon]], or embryonic leaf, in their [[seed]]s.