Monocotyledons (/ˌmɒnəˌkɒtəˈliːdənz/),[d][13][14] commonly referred to asmonocots, (Lilianaesensu Chase & Reveal) areflowering plants whoseseeds contain only oneembryonic leaf, orcotyledon. A monocottaxon has been in use for several decades, but with various ranks and under several different names. TheAPG IV system recognises itsmonophyly but does not assign it to a taxonomic rank, and instead uses the term "monocots" to refer to the group.
Monocotyledons are contrasted with thedicotyledons, which have two cotyledons. Unlike the monocots however, the dicots are notmonophyletic and the two cotyledons are instead the ancestral characteristic of all flowering plants. Botanists now classify dicots into theeudicots ("true dicots") and severalbasal lineages from which the monocots emerged.
The monocots are extremely important economically, culturally, and ecologically, and make up a majority of plant biomass used in agriculture. Common crops such asdates,onions,garlic,rice,wheat,maize, andsugarcane are all monocots. Thegrasses alone cover over 40% of Earth's land area[e][15] and contribute a significant portion of the human diet. Other monocots, likeorchids,tulips,daffodils, andlilies are commonhouseplants and have been the subjects of several celebrations, holidays, and artworks for thousands of years.
Allium crenulatum (Asparagales), an onion, with typical monocotperianth and parallel leaf venationOnion 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 theirseeds. Historically, this feature was used to contrast the monocots with thedicotyledons or dicots which typically have two cotyledons; however, modern research has shown that the dicots areparaphyletic. 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 thebody plan of the ancestral monocotyledons, whose adaptive advantages are poorly understood, but may have been related to adaption toaquatic habitats, prior toradiation 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.[16]
The most important distinction is their growth pattern, lacking alateral 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, monocots include somearboraceous species that reach great height, length and mass. The latter includeagaves,palms,pandans, andbamboos.[22][23] This creates challenges in water transport that monocots deal with in various ways. Some, such as species ofYucca, develop anomalous secondary growth, while palm trees utilise an anomalous primary growth form described asestablishment growth (seeVascular system). The axis undergoes primary thickening, which progresses frominternode 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 adaptivegrowth forms has resulted (Tillich, Figure 2) fromepiphyticorchids (Asparagales) andbromeliads (Poales) to submarineAlismatales (including the reducedLemnoideae) andmycotrophicBurmanniaceae (Dioscreales) andTriuridaceae (Pandanales). Other forms of adaptation include the climbing vines ofAraceae (Alismatales) which use negative phototropism (skototropism) to locatehost trees (i.e. the darkest area),[24] while some palms such asCalamus manan (Arecales) produce the longest shoots in the plant kingdom, up to 185 m long.[25] Other monocots, particularlyPoales, have adopted atherophytelife form.[26][27][28][29][30]
The cotyledon, the primordial Angiospermleaf 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.[31] The evolution of this monocot characteristic has been attributed to developmental differences in early zonal differentiation rather than meristem activity (leaf base theory).[16][32][33]
The lack of cambium in the primaryroot 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 developrunners andrhizomes, which are creeping shoots. Runners servevegetative propagation, have elongatedinternodes, run on or just below the surface of the soil and in most case bearscale leaves. Rhizomes frequently have an additional storage function and rhizome producing plants are consideredgeophytes (Tillich, Figure 11). Other geophytes developbulbs, 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 betubers orcorms, swollen axes. Tubers may form at the end of underground runners and persist. Corms are short lived vertical shoots with terminalinflorescences and shrivel once flowering has occurred. However, intermediate forms may occur such as inCrocosmia (Asparagales). Some monocots may also produce shoots that grow directly down into the soil, these aregeophilous shoots (Tillich, Figure 11) that help overcome the limited trunk stability of large woody monocots.[34][33][35][16]
In nearly all cases theperigone consists of two alternatingtrimerouswhorls oftepals, beinghomochlamydeous, without differentiation betweencalyx andcorolla. Inzoophilous (pollinated by animals) taxa, both whorls arecorolline (petal-like).Anthesis (the period of flower opening) is usuallyfugacious (short lived). Some of the more persistent perigones demonstratethermonastic opening and closing (responsive to changes in temperature). About two thirds of monocots arezoophilous, predominantly byinsects. These plants need to advertise to pollinators and do so by way ofphaneranthous (showy) flowers. Such optical signalling is usually a function of the tepal whorls but may also be provided bysemaphylls (other structures such asfilaments,staminodes orstylodia which have become modified to attract pollinators). However, some monocot plants may haveaphananthous (inconspicuous) flowers and still be pollinated by animals. In these the plants rely either on chemical attraction or other structures such as colouredbracts 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]
Comparison of a monocot (grass:Poales) sprouting (left) with a dicot (right)[f]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 formonocots versuseudicots.[35][36][37]
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.[36] For example, trimerous flowers and monosulcate pollen are also found inmagnoliids,[35] and exclusively adventitious roots are found in some of thePiperaceae.[35] 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 (an orchid), and theDioscoreales (yams).[35]Potamogeton andParis 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.[36] Nevertheless, this list of traits is generally valid, especially when contrasting monocots witheudicots, rather than non-monocot flowering plants in general.[35]
Monocotapomorphies (characteristics derived duringradiation rather than inherited from an ancestral form) includeherbaceous habit, leaves with parallel venation and sheathed base, an embryo with a single cotyledon, anatactostele, numerous adventitious roots,sympodial growth, and trimerous (3 parts perwhorl) flowers that arepentacyclic (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, probablyplesiomorphic.[37]
The distinctive features of the monocots have contributed to the relative taxonomic stability of the group.Douglas E. Soltis and others[38][39][40][41] identify thirteensynapomorphies (shared characteristics that unite monophyletic groups of taxa);
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 anatactostele in which the vascular tissue is scattered rather than arranged in concentric rings.Collenchyma is absent in monocot stems, roots and leaves. Many monocots areherbaceous and do not have the ability to increase the width of a stem (secondary growth) via the same kind ofvascular cambium found in non-monocotwoody plants.[35] However, some monocots do have secondary growth; because this does not arise from a single vascular cambium producingxylem inwards and phloem outwards, it is termed "anomalous secondary growth".[43] 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, andCordyline.[35]
Monocots were first recognized as a group inMatthias de l'Obel'sStirpium adversaria nova. Searching for non-pharmacological characteristics to classify plants by, he chose onleaf form andvenation, and observed that the majority of plants had broad leaves with net-like venation, but some had long and straight leaves with parallel veins.[44] 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.[45][46][47][48]
Formal description dates fromJohn Ray's studies ofseed structure in the 17th century. Ray, who is often considered the first botanicalsystematist,[49] observed thedichotomy ofcotyledon structure in his examination of seeds. He reported his findings in a paper read to theRoyal Society on 17 December 1674, entitled "A Discourse on the Seeds of Plants".[35]
A Discourse on the Seeds of Plants
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... 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... 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... 2. Such which neither spring out of the ground with seed leaves nor have their pulp divided into lobes
Since this paper appeared a year before the publication ofMalpighi'sAnatome Plantarum (1675–1679), Ray has the priority. At the time, Ray did not fully realise the importance of his discovery[51] but progressively developed this over successive publications. And since these were in Latin, "seed leaves" becamefolia seminalia[52] and thencotyledon, followingMalpighi.[53][54] Malpighi and Ray were familiar with each other's work,[51] and Malpighi in describing the same structures had introduced the term cotyledon,[55] which Ray adopted in his subsequent writing.
De seminum vegetatione
Mense quoque Maii, alias seminales plantulas Fabarum, & Phaseolorum, ablatis pariter binis seminalibus foliis, seu cotyledonibus, incubandas posui In the month of May, also, I incubated two seed plants,Faba andPhaseolus, after removing the two seed leaves, or cotyledons
In this experiment, Malpighi also showed that the cotyledons were critical to the development of the plant, proof that Ray required for his theory.[56] In hisMethodus plantarum nova[57] Ray also developed and justified the "natural" or pre-evolutionary approach to classification, based on characteristics selecteda posteriori in order to group together taxa that have the greatest number of shared characteristics. This approach, also referred to as polythetic would last tillevolutionary theory enabledEichler to develop thephyletic system that superseded it in the late nineteenth century, based on an understanding of the acquisition of characteristics.[58][59][60] He also made the crucial observationEx 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.[61][56] He illustrated this by quoting from Malpighi and including reproductions of Malpighi's drawings of cotyledons (see figure).[62] 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,[63] coining the termsMonocotyledones andDicotyledones in 1703,[64] in the revised version of hisMethodus (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).[65]
AlthoughLinnaeus (1707–1778) did not utilise Ray's discovery, basing his own classification solely onfloral reproductive morphology, the term was used shortly after his classification appeared (1753) byScopoli and who is credited for its introduction.[h] Everytaxonomist since then, starting withDe Jussieu andDe Candolle, has used Ray's distinction as a major classification characteristic.[i][34] InDe Jussieu's system (1789), he followed Ray, arranging his Monocotyledones into three classes based on stamen position and placing them betweenAcotyledones and Dicotyledones.[69]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 hisMonocotylédonés (Monocotyledoneae).[3]Lindley (1830) followed De Candolle in using the terms Monocotyledon and Endogenae[j] interchangeably. They considered the monocotyledons to be a group ofvascular plants (Vasculares) whose vascular bundles were thought to arise from within (Endogènes orendogenous).[70]
Monocotyledons remained in a similar position as a major division of the flowering plants throughout the nineteenth century, with minor variations.George Bentham andHooker (1862–1883) used Monocotyledones, as wouldWettstein,[71] whileAugust Eichler used Mononocotyleae[10] andEngler, following de Candolle, Monocotyledoneae.[72] In the twentieth century, some authors used alternative names such asBessey's (1915) Alternifoliae[2] andCronquist's (1966) Liliatae.[1] Later (1981) Cronquist changed Liliatae to Liliopsida,[73] usages also adopted byTakhtajan simultaneously.[33]Thorne (1992)[8] andDahlgren (1985)[74] 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 theICBN allows either adescriptive botanical name or a name formed from the name of an included family.
In summary they have been variously named, as follows:
Over the 1980s, a more general review of the classification ofangiosperms was undertaken. The 1990s saw considerable progress in plantphylogenetics andcladistic theory, initially based onrbcL gene sequencing and cladistic analysis, enabling aphylogenetic tree to be constructed for the flowering plants.[75] The establishment of major newclades 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 onplant evolution and necessitated a major taxonomic restructuring.[76][77]
ThisDNA basedmolecular phylogenetic research confirmed on the one hand that the monocots remained as a well definedmonophyletic group orclade, in contrast to the other historical divisions of the flowering plants, which had to be substantially reorganized.[35] 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.[78] Correlation with morphological criteria showed that the defining feature was not cotyledon number but the separation of angiosperms into two majorpollen types,uniaperturate (monosulcate and monosulcate-derived) and triaperturate (tricolpate and tricolpate-derived), with the monocots situated within the uniaperturate groups.[75] The formal taxonomic ranking of Monoctyledons thus became replaced with monocots as an informal clade.[79][35] This is the name that has been most commonly used since the publication of theAngiosperm Phylogeny Group(APG) system in 1998 and regularly updated since.[76][80][77][81][82][83]
Within the angiosperms, there are two majorgrades, a small early branchingbasal grade, thebasal angiosperms (ANA grade) with threelineages and a larger late branching grade, thecore angiosperms (mesangiosperms) with five lineages, as shown in thecladogram.
Cladogram I: Phylogenetic position of the monocots within the angiosperms in APG IV (2016)[83]
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.[34]
Historically,Bentham (1877), considered the monocots to consist of fouralliances, Epigynae, Coronariae, Nudiflorae and Glumales, based on floral characteristics. He describes the attempts to subdivide the group since the days ofLindley as largely unsuccessful.[84] Like most subsequent classification systems it failed to distinguish between two major orders,Liliales andAsparagales, now recognised as quite separate.[85] A major advance in this respect was the work ofRolf Dahlgren (1980),[86] which would form the basis of theAngiosperm Phylogeny Group's (APG) subsequent modern classification of monocot families. Dahlgren who used the alternate nameLilliidae considered the monocots as asubclass ofangiosperms characterised by a single cotyledon and the presence of triangular protein bodies in thesieve tubeplastids. He divided the monocots into sevensuperorders, Alismatiflorae, Ariflorae, Triuridiflorae,Liliiflorae, Zingiberiflorae, Commeliniflorae and Areciflorae. With respect to the specific issue regarding Liliales and Asparagales, Dahlgren followedHuber (1969)[87] in adopting asplitter approach, in contrast to the longstanding tendency to viewLiliaceae as a very broadsensu latofamily. 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 thesuffix-florae was replaced with-anae (e.g.Alismatanae) and the number of superorders expanded to ten with the addition of Bromelianae, Cyclanthanae and Pandananae.[88]
Molecular studies have both confirmed themonophyly of the monocots and helped elucidate relationships within this group. TheAPG system does not assign the monocots to a taxonomic rank, instead recognizing a monocots clade.[89][90][91][92] 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.[93][83] These form three grades, thealismatid monocots,lilioid monocots and thecommelinid monocots by order of branching, from early to late. In the followingcladogram numbers indicatecrown group (most recent common ancestor of the sampled species of the clade of interest) divergence times inmya (million years ago).[94]
Cladogram 2: The phylogenetic composition of the monocots[83][95]
Of some 70,000species,[96] by far the largest number (65%) are found in twofamilies, 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 Poalesorder include theCyperaceae (sedges) andJuncaceae (rushes), and the monocots also include familiar families such as the palms (Arecaceae, Arecales) and lilies (Liliaceae,Liliales).[85][97]
Inprephyletic 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 thesystem of Eichler 1875–1878 onwards) the predominant theory of monocot origins was the ranalean (ranalian) theory, particularly in the work ofBessey (1915),[2] which traced the origin of all flowering plants to a Ranalean type, and reversed the sequence making dicots the more primitive group.[34]
The monocots form amonophyletic group arising early in the history of theflowering plants, but the fossil record is meagre.[98] The earliest fossils presumed to be monocot remains date from theearly Cretaceous period. For a very long time,fossils of palm trees were believed to be the oldest monocots,[99] first appearing 90 million years ago (mya), but this estimate may not be entirely true.[100] At least some putative monocot fossils have been found in strata as old as the eudicots.[101] The oldest fossils that are unequivocally monocots are pollen from the LateBarremian–Aptian – EarlyCretaceous period, about 120-110 million years ago, and are assignable toclade-Pothoideae-Monstereae Araceae; being Araceae, sister to otherAlismatales.[102][103][104] They have also found flower fossils of Triuridaceae (Pandanales) in Upper Cretaceous rocks in New Jersey,[102] becoming the oldest known sighting ofsaprophytic/mycotrophic habits inangiosperm plants and among the oldest known fossils of monocotyledons.
Topology of the angiospermphylogenetic 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.[105]
Kåre Bremer, usingrbcL sequences and themean path length method for estimatingdivergence times, estimated the age of the monocot crown group (i.e. the time at which the ancestor of today'sAcorus diverged from the rest of the group) as 134 million years.[106][107] Similarly, Wikströmet al.,[108] using Sanderson'snon-parametric rate smoothing approach,[109] obtained ages of 127–141 million years for the crown group of monocots.[110] All these estimates have large error ranges (usually 15–20%), and Wikströmet al. used only a single calibration point,[108] namely the split betweenFagales andCucurbitales, which was set to 84 Ma, in the lateSantonian period. Early molecular clock studies using strict clock models had estimated the monocot crown age to 200 ± 20 million years ago[111] or 160 ± 16 million years,[112] while studies using relaxed clocks have obtained 135-131 million years[113] or 133.8 to 124 million years.[114] Bremer's estimate of 134 million years[106] has been used as a secondary calibration point in other analyses.[115] Some estimates place the diversification of the monocots as far back as 150 mya in theJurassic period.[21]
The lineage that led to monocots (stem group) split from other plants about 136 million years ago[116] or 165–170 million years ago.[21]
The age of the core group of so-called 'nuclear monocots' or 'core monocots', which correspond to all orders exceptAcorales and Alismatales,[117] 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 andLiliales clades appeared), including the crownPetrosaviaceae group may be in the period around 125–120 million years BC (about 111 million years so far[106]), and stem groups of all other orders, includingCommelinidae would have diverged about or shortly after 115 million years.[115] These and many clades within these orders may have originated in southernGondwana, i.e. Antarctica, Australasia, and southern South America.[118]
The aquatic monocots of Alismatales have commonly been regarded as "primitive".[119][120][121][73][122][123][124][125][126] They have also been considered to have the most primitive foliage, which were cross-linked as Dioscoreales[74] andMelanthiales.[8][127] Keep in mind that the "most primitive" monocot is not necessarily "the sister of everyone else".[105] 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 manymorphologicalautapomorphies. 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 Chaseet al.[89] and others.[40][128]
Some authors support the idea of an aquatic phase as the origin of monocots.[129] 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 thebiomechanics of living in the water), roots in groups instead of a single root branching (related to the nature of thesubstrate), includingsympodial use, are consistent with a water source. However, while monocots were sisters of the aquaticCeratophyllales, 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 is difficult to relate their morphology, anatomy and development and those of broad-leaved angiosperms.[130][131]
In the past, taxa which hadpetiolate leaves withreticulate venation were considered "primitive" within the monocots, because of the superficial resemblance to the leaves ofdicotyledons. 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.[68][132][133][134] Among the taxa involved wereSmilax,Trillium (Liliales),Dioscorea (Dioscoreales), etc. A number of these plants arevines that tend to live in shaded habitats for at least part of their lives, and this fact may also relate to their shapelessstomata.[135] 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").[133][134]
The name monocotyledons is derived from the traditional botanical name "Monocotyledones" orMonocotyledoneae inLatin, which refers to the fact that most members of this group have onecotyledon, or embryonic leaf, in theirseeds.
Some monocots, such as grasses, havehypogeal emergence, where the mesocotyl elongates and pushes the coleoptile (which encloses and protects the shoot tip) toward the soil surface.[136] Since elongation occurs above the cotyledon, it is left in place in the soil where it was planted. Many dicots haveepigeal 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.
Monocots are among the most important plants economically and culturally, and account for most of thestaple foods of the world, such ascerealgrains andstarchy root crops, and palms, orchids and lilies,building materials, and manymedicines.[105] Of the monocots, the grasses are of enormous economic importance as a source of animal and human food,[85] and form the largest component of agricultural species in terms ofbiomass produced.[97][138]
^In 1964, Takhtajan proposed that classes including Monocotyledons, be formally named with the suffix-atae, so that the principle oftypification 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".
^Monocots showhypogeal development in which the cotyledon remains invisible within the seed, underground. The visible part is the first true leaf produced from themeristem
^* Lacking inAcorus, so that if this genus issister to the rest of the monocots, the synapomorphies do not apply to monocots as a whole.
^Scopoli, in his treatment of Linnaeus' scheme comments in theHexandria polygynia on the fact thatAlisma is a member of theGens monocotyledon[66]
^See alsoLindley's review of classification systems up to 1853,[67] andDahlgren's from 1853–1982[68]
Takhtajan, Armen Leonovich (1966)."Lilianae".Система и филогения цветкорых растений (Sistema i filogeniia tsvetkovykh rastenii) [Systema et Phylogemia Magnoliophytorum] (in Russian). trans. C Jeffrey, asFlowering plants: Origin and dispersal, Edinburgh: Oliver and Boyd, 1969. Moscow: Наука. p. 473.ISBN0-05-001715-2. Retrieved14 August 2015.
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