Monocotyledon

Source: Wikipedia, the free encyclopedia.
Monocotyledons
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
Lilium
Orders
  • commelinid
    monocots
Synonyms

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

sedges
are also monocots.

In

, and many other common food and decorative crops.

Description

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

General

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.

Vegetative

Organisation, growth and life forms

The most important distinction is their growth pattern, lacking a

Leaves

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]

Reproductive

Flowers

In nearly all cases the

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.
[17]

Fruit and seed

The

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
Mostly
arboraceous
Herbaceous or arboraceous
Leaves[16]
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
adventitial
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
regions
Ring of primary bundles with cambium, differentiated into cortex and stele (eustelic)
Flowers
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)
Monocolpate
(single aperture or colpus)
Tricolpate
(three)
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]

Apomorphies

Monocot

Synapomorphies

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

synapomorphies
(shared characteristics that unite monophyletic groups of taxa);

  1. raphides
  2. Absence of vessels in leaves
  3. Monocotyledonous
    anther
    wall formation*
  4. Successive
    microsporogenesis
  5. Parietal placentation
  6. Monocotyledonous seedling
  7. Persistent radicle
  8. Haustorial cotyledon tip[41]
  9. Open cotyledon sheath
  10. Steroidal
    saponins
    *
  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]

Taxonomy

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

Pre-Linnean

Malpighi

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

Although

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]

This

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]
angiosperms

Amborellales

Nymphaeales

Austrobaileyales

      

magnoliids

Chloranthales

monocots

Ceratophyllales

eudicots

basal angiosperms
core angiosperms

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.[33]

Historically,

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 
MYA
)
          

Acorales

Alismatales

122 MYA
          

Petrosaviales

120 MYA

Dioscoreales (115 MYA)

Pandanales (91 MYA)

Liliales (121 MYA)

121 MYA

Asparagales (120 MYA)

commelinids (118 MYA)
          

Arecales

          

Poales

          

Zingiberales

Commelinales

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]

Evolution

In

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

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.[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]

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 seeds.

Ecology

Emergence

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.

Conservation

The

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

Uses

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

Notes

  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)

Citations

  1. ^ a b c d e Cronquist, Takhtajan & Zimmermann 1966.
  2. ^ a b c Bessey 1915.
  3. ^ a b de Candolle 1819.
  4. ^ Tropicos 2015, Lilianae
  5. ^ a b Takhtajan 1966.
  6. ^ Takhtajan 1964.
  7. ^ Tropicos 2015, Liliidae
  8. ^ a b c Thorne 1992a.
  9. ^ Tropicos 2015, Liliopsida
  10. ^ a b Eichler 1886.
  11. ^ Tropicos 2015, Monocotylondoneae
  12. ^ de Candolle 1818–1821.
  13. ^ "monocotyledon". Merriam-Webster.com Dictionary.
  14. ^ "monocotyledon". Dictionary.com Unabridged (Online). n.d.
  15. ^ a b c Tillich 1998.
  16. ^ a b c Rudall & Buzgo 2002.
  17. ^ a b Vogel 1998.
  18. ^ Kubitzki & Huber 1998.
  19. ^ Kubitzki 1998.
  20. ^ Davis et al. 2013.
  21. ^ a b c Zeng et al 2014.
  22. ^ Du et al 2016.
  23. ^ Soltis & Soltis 2016.
  24. ^ Strong & Ray 1975.
  25. ^ Dransfield 1978.
  26. ^ Tillich 1998, Figure 1
  27. ^ Mauseth 2017, Anomalous forms of growth pp. 211–219
  28. ^ Petit et al 2014.
  29. ^ Tomlinson & Esler 1973.
  30. ^ Leck et al 2008.
  31. ^ Tomlinson 1970.
  32. ^ a b c d Takhtajan 2009, Liliopsida pp. 589–750
  33. ^ a b c d Kubitzki, Rudall & Chase 1998, A brief history of monocot classification p. 23
  34. ^ a b c d e f g h i j k Chase 2004.
  35. ^ a b c NBGI 2016, Monocots versus Dicots.
  36. ^ a b Stevens 2015.
  37. ^ Soltis et al. 2005, p. 92.
  38. ^ Donoghue & Doyle 1989b.
  39. ^ a b Loconte & Stevenson 1991.
  40. ^ Doyle & Donoghue 1992.
  41. ^ Lersten 2004.
  42. ^ Donoghue 2005.
  43. ^ a b c d e Soltis et al. 2005.
  44. ^ l'Obel 1571, p. 65
  45. ^ Vines 1913, p. 10.
  46. ^ Hoeniger & Hoeniger 1969.
  47. ^ Pavord 2005, p. 339
  48. ^ Pavord 2005.
  49. ^ Ray 1674, pp. 164, 166.
  50. ^ a b Raven 1950.
  51. ^ Ray 1682, De foliis plantarum seminalibus dictis p. 7.
  52. ^ Short & George 2013, p. 15.
  53. ^ Ray 1682, De plantula seminali reliquisque femine contentis p. 13.
  54. ^ a b Malpighi 1679, De seminum vegetatione p. 18.
  55. ^ a b Bewley, Black & Halmer 2006, History of seed research p. 334.
  56. ^ Ray 1682.
  57. ^ Stuessy 2009, Natural classification p. 47.
  58. ^ Datta 1988, Systems of classification p. 21.
  59. ^ Stace 1989, The development of plant taxonomy p. 17.
  60. ^ Raven 1950, p. 195.
  61. ^ Ray 1682, De foliis plantarum seminalibus dictis p. 11.
  62. ^ Ray 1696.
  63. ^ Ray 1703, pp. 1–2.
  64. ^ Ray 1703, p. 16.
  65. ^ Scopoli 1772, Alisma pp. 266–267
  66. ^ Lindley 1853.
  67. ^ a b Dahlgren & Clifford 1982.
  68. ^ Jussieu 1789.
  69. ^ Lindley 1830.
  70. ^ Wettstein 1924.
  71. ^ Engler 1886.
  72. ^ a b Cronquist 1981.
  73. ^ a b Dahlgren, Clifford & Yeo 1985.
  74. ^ a b Chase et al 1993.
  75. ^ a b APG 1998.
  76. ^ a b APG III 2009.
  77. ^ Bremer & Wanntorp 1978.
  78. ^ Chase et al. 1995b.
  79. ^ APG II 2003.
  80. ^ LAPGIII 2009.
  81. ^ Chase & Reveal 2009.
  82. ^ a b c d APG IV 2016.
  83. ^ Bentham 1877.
  84. ^ a b c Fay 2013.
  85. ^ Dahlgren 1980.
  86. ^ Huber 1969.
  87. ^ Dahlgren 1989.
  88. ^ a b Chase et al 1995.
  89. ^ Chase et al 2000.
  90. ^ Davis et al 2004.
  91. ^ Soltis & Soltis 2004.
  92. ^ Cantino et al 2007.
  93. ^ Hertwick et al. 2015.
  94. ^ Givnish et al 2018.
  95. ^ CoL 2015, Liliopsida
  96. ^ a b Panis 2008.
  97. ^ Ganfolfo et al 1998.
  98. ^ Smith et al 2010, p. 38.
  99. ^ Herendeen & Crane 1995.
  100. ^ Herendeen, Crane & Drinnan 1995.
  101. ^ a b Gandolfo, Nixon & Crepet 2002.
  102. ^ Friis, Pedersen & Crane 2004.
  103. ^ Friis, Pedersen & Crane 2006.
  104. ^ a b c Bremer 2000.
  105. ^ Bremer 2002.
  106. ^ a b Wikström, Savolainen & Chase 2001.
  107. ^ Sanderson 1997.
  108. ^ Sanderson et al 2004.
  109. ^ Savard et al 1994.
  110. ^ Goremykin, Hansman & Martin 1997.
  111. ^ Leebens-Mack et al 2005.
  112. ^ Moore et al 2007.
  113. ^ a b Janssen & Bremer 2004.
  114. ^ Hedges & Kumar 2009, p. 205.
  115. ^ Bremer & Janssen 2006.
  116. ^ Hallier 1905.
  117. ^ Arber 1925.
  118. ^ Hutchinson 1973.
  119. ^ Cronquist 1988.
  120. ^ Takhtajan 2009.
  121. ^ Takhtajan 1991.
  122. ^ Stebbins 1974.
  123. ^ Thorne 1976.
  124. ^ Thorne 1992b.
  125. ^ Stevenson & Loconte 1995.
  126. ^ Henslow 1893.
  127. ^ Zimmermann & Tomlinson 1972.
  128. ^ Tomlinson 1995.
  129. ^ Patterson & Givnish 2002.
  130. ^ a b Givnish et al. 2005.
  131. ^ a b Givnish et al. 2006.
  132. ^ Cameron & Dickison 1998.
  133. ^ Radosevich et al 1997, p. 149.
  134. ^ IUCN 2016, Red List summary: All plant classes and families
  135. ^ Tang et al 2016.

Bibliography

Books

Historical

Modern

Symposia

Chapters

Articles

Phylogenetics

APG

Websites and databases

External links

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