Source: Wikipedia, the free encyclopedia.
Temporal range: Early Cretaceous – Recent
Diversity of monocots which includes wheat (Triticum), taro (Colocasia esculenta), date palm, (Phoenix dactylifera), Zostera marina, lily (Lilium), Pandanus heterocarpus, and ginger (Zingiber officinale)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Type genus
  • commelinid

Monocotyledons (

grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of the major groups into which the flowering plants have traditionally been divided; the rest of the flowering plants have two cotyledons and are classified as dicotyledons
, or dicots.

Monocotyledons have almost always been recognized as a group, but with various

taxonomic ranks and under several different names. The APG III system
of 2009 recognises a clade called "monocots" but does not assign it to a taxonomic rank.

The monocotyledons include about 70,000 species, about a quarter of all angiosperms. The largest

are also monocots.


, and many other common food and decorative crops.


Allium crenulatum (Asparagales), an onion, with typical monocot perianth and parallel leaf venation
Onion slice: the cross-sectional view shows the veins that run in parallel along the length of the bulb and stem


The monocots or monocotyledons have, as the name implies, a single (mono-)

clades are rare.[16]

Thus monocots are distinguishable from other angiosperms both in terms of their uniformity and diversity. On the one hand, the organization of the shoots, leaf structure, and floral configuration are more uniform than in the remaining angiosperms, yet within these constraints a wealth of diversity exists, indicating a high degree of evolutionary success.


Organisation, growth and life forms

The most important distinction is their growth pattern, lacking a


The cotyledon, the primordial Angiosperm

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.[31] The evolution of this monocot characteristic has been attributed to developmental differences in early zonal differentiation rather than meristem activity (leaf base theory).[15][16][32]

Roots and underground organs

The lack of cambium in the primary

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 geophilous shoots (Tillich, Figure 11) that help overcome the limited trunk stability of large woody monocots.[33][32][34][15]



In nearly all cases the

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.

Fruit and seed


vascular bundles.[32]

Comparison with dicots

grass: Poales) sprouting (left) with a dicot (right)[e]
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.[34][35][36]

Feature In monocots In dicots
Growth form
Herbaceous or arboraceous
stipules absent. Major leaf veins usually parallel
Broad, seldom sheathed, petiole common often with stipules. Veins usually reticulate (pinnate or palmate)
Roots Primary root of short duration, replaced by
roots forming fibrous or fleshy root systems
Develops from the radicle. Primary root often persists forming strong taproot and secondary roots
Vascular bundles
Numerous scattered bundles in
ground parenchyma, cambium rarely present, no differentiation between cortical and stelar
Ring of primary bundles with cambium, differentiated into cortex and stele (eustelic)
Parts in threes (trimerous) or multiples of three (e.g. 3, 6 or 9 petals) Fours (tetramerous) or fives (pentamerous)
Pollen: Number of apertures (furrows or pores)
(single aperture or colpus)
Embryo: Number of cotyledons (leaves in the seed
One, endosperm frequently present in seed Two, endosperm present or absent

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.

eudicots, rather than non-monocot flowering plants in general.[34]




The distinctive features of the monocots have contributed to the relative taxonomic stability of the group.

(shared characteristics that unite monophyletic groups of taxa);

  1. raphides
  2. Absence of vessels in leaves
  3. Monocotyledonous
    wall formation*
  4. Successive
  5. Parietal placentation
  6. Monocotyledonous seedling
  7. Persistent radicle
  8. Haustorial cotyledon tip[41]
  9. Open cotyledon sheath
  10. Steroidal
  11. Fly pollination*
  12. Diffuse vascular bundles and absence of secondary growth[f]

Vascular system

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

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 plants.[34] 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".[42] 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, and Cordyline.[34]


The monocots form one of five major lineages of

radiations accounting for 22.8% and 74.2% of all angiosperm species respectively.[43]

Of these, the grass family (Poaceae) is the most economically important, which together with the orchids

Orchidaceae account for half of the species diversity, accounting for 34% and 17% of all monocots respectively and are among the largest families of angiosperms. They are also among the dominant members of many plant communities.[43]

Early history



The monocots are one of the major divisions of the

venation. He observed that the majority had broad leaves with net-like venation, but a smaller group were grass-like plants with long straight parallel veins.[44] In doing so he distinguished between the dicotyledons, and the latter (grass-like) monocotyledon group, although he had no formal names for the two groups.[45][46][47]

Formal description dates from

systematist,[48] 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".[34]

Since this paper appeared a year before the publication of

Malpighi.[52][53] Malpighi and Ray were familiar with each other's work,[50] and Malpighi in describing the same structures had introduced the term cotyledon,[54]
which Ray adopted in his subsequent writing.

In this experiment, Malpighi also showed that the cotyledons were critical to the development of the plant, proof that Ray required for his theory.

phyletic system that superseded it in the late nineteenth century, based on an understanding of the acquisition of characteristics.[57][58][59] 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.[60][55] He illustrated this by quoting from Malpighi and including reproductions of Malpighi's drawings of cotyledons (see figure).[61] 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,[62] coining the terms Monocotyledones and Dicotyledones in 1703,[63] 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).[64]

Post Linnean


Monocotyledons remained in a similar position as a major division of the flowering plants throughout the nineteenth century, with minor variations.

Thorne (1992)[8] and Dahlgren (1985)[73]
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

or a name formed from the name of an included family.

In summary they have been variously named, as follows:

Modern era

Over the 1980s, a more general review of the classification of

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.[75][76]


monosulcate and monosulcate-derived) and triaperturate (tricolpate and tricolpate-derived), with the monocots situated within the uniaperturate groups.[74] The formal taxonomic ranking of Monoctyledons thus became replaced with monocots as an informal clade.[78][34] This is the name that has been most commonly used since the publication of the Angiosperm Phylogeny Group (APG) system in 1998 and regularly updated since.[75][79][76][80][81][82]

Within the angiosperms, there are two major

core angiosperms (mesangiosperms) with five lineages, as shown in the cladogram

Cladogram I: Phylogenetic position of the monocots within the angiosperms in APG IV (2016)[82]










basal angiosperms
core angiosperms


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.[33]


Alismatanae) and the number of superorders expanded to ten with the addition of Bromelianae, Cyclanthanae and Pandananae.[87]

Molecular studies have both confirmed the monophyly of the monocots and helped elucidate relationships within this group. The APG system does not assign the monocots to a taxonomic rank, instead recognizing a monocots clade.[88][89][90][91] However, there has remained some uncertainty regarding the exact relationships between the major lineages, with a number of competing models (including APG).[21]

The APG system establishes eleven orders of monocots.

mya (million years ago).[93]

Cladogram 2: The phylogenetic composition of the monocots[82][94]
monocots (131 



122 MYA


120 MYA

Dioscoreales (115 MYA)

Pandanales (91 MYA)

Liliales (121 MYA)

121 MYA

Asparagales (120 MYA)

commelinids (118 MYA)







Of some 70,000

Orchidaceae, Asparagales) contain about 25,000 species and the grasses (Poaceae, Poales) about 11,000. Other well known groups within the Poales 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).[84][96]



Bessey (1915),[2] which traced the origin of all flowering plants to a Ranalean type, and reversed the sequence making dicots the more primitive group.[33]

The monocots form a

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.[43]

Molecular clock estimates

rbcL sequences and the mean path length method for estimating 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.[104][105] Similarly, Wikström et al.,[106] using Sanderson's non-parametric rate smoothing approach,[107] obtained ages of 127–141 million years for the crown group of monocots.[108] All these estimates have large error ranges (usually 15-20%), and Wikström et al. used only a single calibration point,[106] namely the split between Fagales and Cucurbitales, which was set to 84 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[109] or 160 ± 16 million years,[110] while studies using relaxed clocks have obtained 135-131 million years[111] or 133.8 to 124 million years.[112] Bremer's estimate of 134 million years[104] has been used as a secondary calibration point in other analyses.[113] Some estimates place the emergence of the monocots as far back as 150 mya in the Jurassic period.[21]

Core group

The age of the core group of so-called 'nuclear monocots' or 'core monocots', which correspond to all orders except

Commelinidae would have diverged about or shortly after 115 million years.[113] These and many clades within these orders may have originated in southern Gondwana, i.e. Antarctica, Australasia, and southern South America.[115]

Aquatic monocots

The aquatic monocots of Alismatales have commonly been regarded as "primitive".[116][117][118][72][119][120][121][122][123] They have also been considered to have the most primitive foliage, which were cross-linked as Dioscoreales[73] and Melanthiales.[8][124] Keep in mind that the "most primitive" monocot is not necessarily "the sister of everyone else".[43] 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 morphological 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.[88] and others.[39][125]

Some authors support the idea of an aquatic phase as the origin of monocots.

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.[127][128]

Other taxa

In the past, taxa which had

stomata.[132] 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").[130][131]


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 seeds.



Some monocots, such as grasses, have hypogeal emergence, where the mesocotyl elongates and pushes the coleoptile (which encloses and protects the shoot tip) toward the soil surface.[133] Since elongation occurs above the cotyledon, it is left in place in the soil where it was planted. Many dicots have epigeal emergence, in which the hypocotyl elongates and becomes arched in the soil. As the hypocotyl continues to elongate, it pulls the cotyledons upward, above the soil surface.



near threatened of 4,492 whose status is known.[134]


Monocots are among the most important plants economically and culturally, and account for most of the

medicines.[43] Of the monocots, the grasses are of enormous economic importance as a source of animal and human food,[84] and form the largest component of agricultural species in terms of biomass produced.[96][135]

Other economically important monocotyledon

, are monocotyledons.

See also


  1. ^ In 1964, Takhtajan proposed that classes including Monocotyledons, be formally named with the suffix -atae, so that the principle of typification resulted in Liliatae for monocotyledons.[6] The proposal was formally described in 1966 by Cronquist, Takhtajan and Zimmermann,[1] from which is derived the descriptor "liliates".
  2. J.H. Schaffn. 1911[7]
  3. ^ Cronquist[1] attributes this term to De Candolle as DC. 1818 Syst. 1: 122[12]
  4. required.)
  5. ^ 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
  6. ^ * Lacking in Acorus, so that if this genus is sister to the rest of the monocots, the synapomorphies do not apply to monocots as a whole.
  7. ^ Scopoli, in his treatment of Linnaeus' scheme comments in the Hexandria polygynia on the fact that Alisma is a member of the Gens monocotyledon[65]
  8. ^ See also Lindley's review of classification systems up to 1853,[66] and Dahlgren's from 1853–1982[67]
  9. ^ Endogènes (ενδον within + γεναω I create)


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  4. ^ Tropicos 2015, Lilianae
  5. ^ a b Takhtajan 1966.
  6. ^ Takhtajan 1964.
  7. ^ Tropicos 2015, Liliidae
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  9. ^ Tropicos 2015, Liliopsida
  10. ^ a b Eichler 1886.
  11. ^ Tropicos 2015, Monocotylondoneae
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  13. ^ "monocotyledon". Dictionary.
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Websites and databases

External links

  • Data related to Monocots at Wikispecies
  • Media related to Monocots at Wikimedia Commons