Editing Monocotyledon (section)

==Description==
[[File:Allium crenulatum 5231.JPG|thumb|right|''[[Allium crenulatum]]'' ([[Asparagales]]), an onion, with typical monocot [[perianth]] and parallel leaf venation]]
[[Image:Onion slice.jpg|thumb|Onion slice: the cross-sectional view shows the veins that run in parallel along the length of the bulb and stem]]
The monocots have, as the name implies, a single (mono-) [[cotyledon]], or embryonic leaf, in their [[seed]]s. Historically, this feature was used to contrast the monocots with the [[dicotyledon]]s or dicots which typically have two cotyledons; however, modern research has shown that the dicots are [[Paraphyly|paraphyletic]]. From a diagnostic point of view the number of cotyledons is neither a particularly useful characteristic (as they are only present for a very short period in a plant's life), nor is it completely reliable. The single cotyledon is only one of a number of modifications of the [[body plan]] of the ancestral monocotyledons, whose adaptive advantages are poorly understood, but may have been related to adaption to [[aquatic habitats]], prior to [[adaptive radiation|radiation]] to terrestrial habitats. Nevertheless, monocots are sufficiently distinctive that there has rarely been disagreement as to membership of this group, despite considerable diversity in terms of external morphology.{{sfn|Tillich|1998}}

With over 70,000 species, monocots are extremely evolutionarily successful and occupy a diverse set of [[Ecological niche|niches]]:{{sfn|Vogel|1998}} [[Perennial]] [[geophytes]] including [[orchids]] ([[Asparagales]]); [[tulips]] and [[lilies]] ([[Liliales]]); rosette and succulent [[epiphytes]] (Asparagales); [[mycoheterotrophs]] (Liliales, [[Dioscoreales]], [[Pandanales]]), all in the [[lilioid monocots]]; major [[cereal]] [[food grains|grains]] ([[maize]], [[rice]], [[barley]], [[rye]], [[oats]], [[millet]], [[sorghum]] and [[wheat]]) in the [[grass family]]; and forage grasses ([[Poales]]) as well as [[woody plants|woody]] tree-like [[palm trees]] ([[Arecales]]), [[bamboo]], [[reed (plant)|reed]]s and [[bromeliads]] (Poales), [[bananas]] and [[ginger]] ([[Zingiberales]]) in the [[commelinid monocots]], as well as floating or submerged [[aquatic plants]] such as [[seagrass]] ([[Alismatales]]) are all monocots.{{sfn|Kubitzki|Huber|1998}}{{sfn|Kubitzki|1998}}{{sfn|Davis et al.|2013}}{{sfn|Zeng et al|2014}}

=== Vegetative ===
====Organisation, growth and life forms====
The most important distinction is their growth pattern, lacking a [[lateral meristem]] ([[cambium]]) that allows for continual growth in diameter with height ([[secondary growth]]), and therefore this characteristic is a basic limitation in shoot construction. Although largely herbaceous, some [[arboraceous]] monocots reach great height, length and mass. The latter include [[agaves]], [[palm (plant)|palms]], [[pandans]], and [[bamboos]].{{sfn|Du et al|2016}}{{sfn|Soltis|Soltis|2016}} This creates challenges in water transport that monocots deal with in various ways. Some, such as species of ''[[Yucca]]'', develop anomalous secondary growth, while palm trees utilise an anomalous primary growth form described as [[:wikt:establishment growth|establishment growth]] (''see'' [[#Vascular system|Vascular system]]). The axis undergoes primary thickening, that progresses from [[internode (botany)|internode]] to internode, resulting in a typical inverted conical shape of the basal primary axis (''see'' Tillich, Figure 1). The limited conductivity also contributes to limited branching of the stems. Despite these limitations a wide variety of adaptive [[growth forms]] has resulted (Tillich, Figure 2) from [[epiphytic]] [[orchids]] (Asparagales) and [[bromeliads]] (Poales) to submarine [[Alismatales]] (including the reduced [[Lemnoideae]]) and [[mycotrophic]] [[Burmanniaceae]] (Dioscreales) and [[Triuridaceae]] (Pandanales). Other forms of adaptation include the climbing vines of [[Araceae]] (Alismatales) which use negative phototropism ([[skototropism]]) to locate [[host (biology)|host]] trees (''i.e.'' the darkest area),{{sfn|Strong|Ray|1975}} while some palms such as ''[[Calamus (palm)|Calamus manan]]'' ([[Arecales]]) produce the longest shoots in the plant kingdom, up to 185&nbsp;m long.{{sfn|Dransfield|1978}} Other monocots, particularly [[Poales]], have adopted a [[therophyte]] [[life form]].<ref name=Tillichfig1/><ref name=MausethAFG/>{{sfn|Petit et al|2014}}{{sfn|Tomlinson|Esler|1973}}{{sfn|Leck et al|2008}}

====Leaves====
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The cotyledon, the primordial Angiosperm [[leaf]] consists of a proximal leaf base or hypophyll and a distal hyperphyll. In monocots the hypophyll tends to be the dominant part in contrast to other angiosperms. From these, considerable diversity arises. Mature monocot leaves are generally narrow and linear, forming a sheathing around the stem at its base, although there are many exceptions. [[Leaf venation]] is of the striate type, mainly arcuate-striate or longitudinally striate (parallel), less often palmate-striate or pinnate-striate with the leaf veins emerging at the leaf base and then running together at the apices. There is usually only one leaf per node because the leaf base encompasses more than half the circumference.{{sfn|Tomlinson|1970}} The evolution of this monocot characteristic has been attributed to developmental differences in early zonal differentiation rather than meristem activity (leaf base theory).{{sfn|Tillich|1998}}{{sfn|Rudall|Buzgo|2002}}<ref name=TakhtajanLiliops/>

====Roots and underground organs====
The lack of cambium in the primary [[root]] limits its ability to grow sufficiently to maintain the plant. This necessitates early development of roots derived from the shoot (adventitious roots). In addition to roots, monocots develop [[stolon|runners]] and [[rhizomes]], which are creeping shoots. Runners serve [[vegetative propagation]], have elongated [[internodes]], run on or just below the surface of the soil and in most case bear [[scale leaves]]. Rhizomes frequently have an additional storage function and rhizome producing plants are considered [[geophytes]] (Tillich, Figure 11). Other geophytes develop [[bulbs]], a short axial body bearing leaves whose bases store food. Additional outer non-storage leaves may form a protective function (Tillich, Figure 12). Other storage organs may be [[tubers]] or [[corms]], swollen axes. Tubers may form at the end of underground runners and persist. Corms are short lived vertical shoots with terminal [[inflorescences]] and shrivel once flowering has occurred. However, intermediate forms may occur such as in ''[[Crocosmia]]'' (Asparagales). Some monocots may also produce shoots that grow directly down into the soil, these are [[wikt:geophilous|geophilous]] shoots (Tillich, Figure 11) that help overcome the limited trunk stability of large woody monocots.<ref name=Kubitzmmonohist/><ref name=TakhtajanLiliops/>{{sfn|Chase|2004}}{{sfn|Tillich|1998}}

=== Reproductive ===
====Flowers====
In nearly all cases the [[perianth|perigone]] consists of two alternating [[trimerous]] [[whorl (botany)|whorls]] of [[tepals]], being [[wikt:homochlamydeous|homochlamydeous]], without differentiation between [[calyx (flower)|calyx]] and [[corolla (flower)|corolla]]. In [[wikt:zoophilous|zoophilous]] (pollinated by animals) taxa, both whorls are [[corolline]] (petal-like). [[Anthesis]] (the period of flower opening) is usually [[wikt:fugacious|fugacious]] (short lived). Some of the more persistent perigones demonstrate [[thermonastic]] opening and closing (responsive to changes in temperature). About two thirds of monocots are [[zoophilous]], predominantly by [[insects]]. These plants need to advertise to pollinators and do so by way of [[Glossary of botanical terms#phaneranthous|phaneranthous]] (showy) flowers. Such optical signalling is usually a function of the tepal whorls but may also be provided by [[semaphylls]] (other structures such as [[stamen|filaments]], [[staminodes]] or [[stylodia]] which have become modified to attract pollinators). However, some monocot plants may have [[Glossary of botanical terms#aphananthous|aphananthous]] (inconspicuous) flowers and still be pollinated by animals. In these the plants rely either on chemical attraction or other structures such as coloured [[bracts]] fulfill the role of optical attraction. In some phaneranthous plants such structures may reinforce floral structures. The production of fragrances for olfactory signalling are common in monocots. The perigone also functions as a landing platform for pollinating insects.
{{sfn|Vogel|1998}}

====Fruit and seed====
The [[embryo#Plant embryos|embryo]] consists of a single cotyledon, usually with two [[vascular bundles]].<ref name=TakhtajanLiliops/>

===Comparison with dicots===
[[File:Monocot vs dicot crop Pengo.jpg|thumb|Comparison of a monocot ([[grass]]: [[Poales]]) sprouting (left) with a dicot (right){{efn|Monocots show [[hypogeal]] development in which the cotyledon remains invisible within the seed, underground. The visible part is the first true leaf produced from the [[meristem]]}}]]
[[File:Joshua Tree 01.jpg|thumb|''[[Yucca brevifolia]]'' (Joshua Tree: Asparagales)
]]
The traditionally listed differences between monocots and dicots are as follows. This is a broad sketch only, not invariably applicable, as there are a number of exceptions. The differences indicated are more true for [[monocots]] versus [[eudicots]].{{sfn|Chase|2004}}{{sfn|NBGI|2016|loc=[http://www.botanicgardens.ie/educ/monodic.pdf Monocots versus Dicots]}}{{sfn|Stevens|2015}}

{| class="wikitable"
|-
! Feature
! In monocots
! In dicots
|-
| [[Growth form]]
| Mostly [[herbaceous]], occasionally [[arboraceous]]
| Herbaceous or arboraceous
|-
| [[Leaves]]{{sfn|Rudall|Buzgo|2002}} 
| [[Leaf shape]] oblong or linear, often sheathed at base, [[petiole (botany)|petiole]] seldom developed, [[stipules]] absent. Major [[leaf#Veins|leaf veins]] usually [[leaf#Venation|parallel]] 
| Broad, seldom sheathed, petiole common often with stipules. Veins usually [[Leaf#Venation|reticulate]] (pinnate or palmate)
|-
| [[Root]]s
| Primary root of short duration, replaced by [[Adventious roots|adventitial]] roots forming fibrous or fleshy root systems 
| Develops from the [[radicle]]. Primary root often persists forming strong taproot and secondary roots
|-
| [[Plant stem]]: [[Vascular bundles]] 
| Numerous scattered bundles in [[ground parenchyma]], [[cambium]] rarely present, no differentiation between [[cortex (botany)|cortical]] and [[stele (biology)|stelar]] regions
| Ring of primary bundles with cambium, differentiated into cortex and stele ([[wikt:eustele|eustelic]])
|-
| [[Flowers]]
| Parts in threes ([[merosity|trimerous]]) or multiples of three (''e.g.'' 3, 6 or 9 petals)
| Fours (tetramerous) or fives (pentamerous)
|-
| [[Pollen]]: Number of [[aperture (botany)|apertures]] (furrows or pores)
| [[Monocolpate]] (single aperture or colpus)
| [[Tricolpate]] (three)
|-
| [[Plant embryo|Embryo]]: Number of [[cotyledon]]s (leaves in the [[seed]])
| One, [[endosperm]] frequently present in seed
| Two, endosperm present or absent
|}
{{multiple image
| header    = Comparison of monocots and dicots
| align     = center
| image1    = Monocot vs Dicot.svg
| caption1  =
| alt1      = Illustrations of differences between monocots and dicots
| width1    = 450
}}

A number of these differences are not unique to the monocots, and, while still useful, no one single feature will infallibly identify a plant as a monocot.{{sfn|NBGI|2016|loc=[http://www.botanicgardens.ie/educ/monodic.pdf Monocots versus Dicots]}} For example, trimerous flowers and monosulcate pollen are also found in [[magnoliid]]s,{{sfn|Chase|2004}} and exclusively adventitious roots are found in some of the [[Piperaceae]].{{sfn|Chase|2004}} Similarly, at least one of these traits, parallel leaf veins, is far from universal among the monocots. Broad leaves and reticulate leaf veins, features typical of dicots, are found in a wide variety of monocot families: for example, ''[[Trillium]]'', ''[[Smilax]]'' (greenbriar), ''[[Pogonia (plant)|Pogonia]]'' (an orchid), and the [[Dioscoreales]] (yams).{{sfn|Chase|2004}} ''[[Potamogeton]]'' and ''[[Paris quadrifolia]]'' (herb-paris) are examples of monocots with tetramerous flowers. Other plants exhibit a mixture of characteristics. [[Nymphaeaceae]] (water lilies) have reticulate veins, a single cotyledon, adventitious roots, and a monocot-like vascular bundle. These examples reflect their shared ancestry.{{sfn|NBGI|2016|loc=[http://www.botanicgardens.ie/educ/monodic.pdf Monocots versus Dicots]}} Nevertheless, this list of traits is generally valid, especially when contrasting monocots with [[eudicot]]s, rather than non-monocot flowering plants in general.{{sfn|Chase|2004}}

=== Apomorphies ===

Monocot [[Glossary of botanical terms#apomorphy|apomorphies]] (characteristics derived during [[adaptive radiation|radiation]] rather than inherited from an ancestral form) include [[herbaceous]] habit, leaves with parallel venation and sheathed base, an embryo with a single cotyledon, an [[stele (biology)|atactostele]], numerous adventitious roots, [[sympodial]] growth, and trimerous (3 parts per [[whorl (botany)|whorl]]) flowers that are [[pentacyclic]] (5 whorled) with 3 sepals, 3 petals, 2 whorls of 3 stamens each, and 3 carpels. In contrast, monosulcate pollen is considered an ancestral trait, probably [[plesiomorphic]].{{sfn|Stevens|2015}}

=== Synapomorphies ===

The distinctive features of the monocots have contributed to the relative taxonomic stability of the group. [[Douglas E. Soltis]] and others{{sfn|Soltis et al.|2005|loc=p.&nbsp;92}}{{sfn|Donoghue|Doyle|1989b}}{{sfn|Loconte|Stevenson|1991}}{{sfn|Doyle|Donoghue|1992}} identify thirteen [[synapomorphies]] (shared characteristics that unite monophyletic groups of taxa);
{{div col|colwidth=30em}}  
# [[Calcium oxalate]] [[raphides]]
# Absence of vessels in leaves
# Monocotyledonous [[anther]] wall formation*
# Successive [[microsporogenesis]]
# [[Syncarpous]] [[gynoecium]]
# Parietal [[placentation]]
# Monocotyledonous [[seedling]]
# Persistent radicle
# [[:wikt:Haustorium|Haustorial]] cotyledon tip{{sfn|Lersten|2004}}
# Open cotyledon sheath
# Steroidal [[saponins]]*
# Fly pollination*
# Diffuse vascular bundles and absence of [[secondary growth]]{{efn|* Lacking in ''[[Acorus]]'', so that if this genus is [[sister group|sister]] to the rest of the monocots, the synapomorphies do not apply to monocots as a whole.}}
{{div col end}}

===Vascular system===
[[File:Royal Palm Trunk.jpg|thumb|''[[Roystonea regia]]'' palm ([[Arecales]]) stems showing anomalous secondary growth in monocots, with characteristic fibrous roots]]

Monocots have a distinctive arrangement of vascular tissue known as an [[Stele (biology)|atactostele]] in which the vascular tissue is scattered rather than arranged in concentric rings. [[Collenchyma]] is absent in monocot stems, roots and leaves. Many monocots are [[herbaceous]] and do not have the ability to increase the width of a stem ([[secondary growth]]) via the same kind of [[vascular cambium]] found in non-monocot [[woody plant]]s.{{sfn|Chase|2004}} However, some monocots do have secondary growth; because this does not arise from a single vascular cambium producing [[xylem]] inwards and phloem outwards, it is termed "anomalous secondary growth".{{sfn|Donoghue|2005}}  Examples of large monocots which either exhibit secondary growth, or can reach large sizes without it, are palms ([[Arecaceae]]), screwpines ([[Pandanaceae]]), bananas ([[Musaceae]]), ''[[Yucca]]'', ''[[Aloe]]'', ''[[Dracaena (plant)|Dracaena]]'', and ''[[Cordyline]]''.{{sfn|Chase|2004}}