Editing Monocotyledon (section)

===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}}