MONOCOTS: CHARACTERISTICS, TAXONOMY, CLASSIFICATION, EXAMPLES - BIOLOGY - 2025

The monocots, also known as liliópsidas, are a class of angiosperms (flowering plants) which brings about 77963 species including palms, grasses (grasses), orchids, lilies and onions, among others.

They are generally herbaceous plants with long and narrow leaves that, unlike dicots, are longer than they are wide. Furthermore, the veins or ribs are parallel.

Monocot leaves are long, narrow, and have parallel venation. Source: pixabay.com

The flowers occur in multiples of three as three sepals, three petals, six stamens, and a pistil with three fused carpels. They are a monophyletic taxon within angiosperms.

It currently comprises 11 orders, among which grass plants (poaceae) stand out as the most abundant and of great economic importance.

characteristics

Appearance

These are herbs (rarely woody) that are mostly fast growing, being a sympodial. They have long and narrow leaves.

On the other hand, they can be recognized by a cross section of the stem, in which the vascular bundles are seen radially dispersed in the medulla, forming two or more rings and not arranged in a ring unlike dicots.

The root system is formed by fibrous roots, adventitious type. Monocots do not have true secondary growth.

The rhizomes or primary stems are very frequent, some underground or creeping, partially erect and sometimes woody.

Leaves

The leaves are long and narrow. The characteristic ribs are parallel to each other, unlike dicotyledons which have cross-linked ribs. These plants have simple leaves and have only one leaf per node.

The foliar base is wide, it does not have stipules. They have an intercalary meristem in the internode and the foliar base.

In the leaves, the stomata are arranged in parallel lines along the entire length of the leaf axis.

The seeds of lilypsids contain a single cotyledon. Source: pixabay.com

flowers

The flowers are presented in multiples of three. For example, three sepals, three petals, six stamens, and the pistil is made up of three fused carpels. In the case of monocots, in several orders there is no clear differentiation between sepals and petals, therefore they are tepals.

In this case, the tepals are in two whorls, each one trinervated, both being alternated.

The flowers have very frequent septal nectaries and the pollen is uniapertured or derived from this type of pollen. In monocots a successive microsporogenesis occurs.

These flowers are grouped in mainly racemose inflorescences, frequently actinomorphic and sometimes zygomorphic (Alstroemeriaceae, Cannaceae, Orchidaceae, Zingiberaceae and Commelinaceae).

Seed

The seeds of this group of plants contain a single pseudoterminal and generally tubular cotyledon, and the presence of endosperm (tissue that nourishes the embryo) is characteristic of them.

The seed has testa, the embryo is long, cylindrical, and the plumule is lateral.

Chemical compounds

The characteristic chemical compounds of monocots are non-hydrolyzable tannins such as epicatequin, ellagitannins, neolignans. As well as hemicelluloses like xylanes, they do not have benzylisoquinoline alkaloids.

Spheroidal protoanthocyanins and saponins are produced by some groups of plants, and calcium oxalate crystals often appear.

Taxonomy

-Kingdom: Plantae

-Subreino: Viridiplantae

-Inferior: Streptophyta

-Superphylum: Embryophyta

-Phylum: Tracheophyta

-Subphylum: Spermatophytina

-Superclass: Angiospermae

-Class: Magnoliopsida

-Superorden: Lilianae (Monocotyledones)

Classification (orders)

Acorales

This order has two species, classified within the Acoraceae family.

Alismatales

It comprises some 3,953 species and groups the families Alismataceae, Aponogetonaceae, Araceae, Butomaceae, Cymodoceaceae, Hydrocharitaceae, Juncaginaceae, Maundiaceae, Posidoniaceae, Potamogetonaceae, Ruppiaceae, Scheuchzeriaceae, Tofieldiaceae, Zosteraceae.

It is comprised of plants with an aquatic habit, floating or partially submerged.

The Elodea sp. it is a plant of the order Alismatales. Source: Christian Fischer

Arecales

It is made up of some 2,577 species and two families: Arecaceae (Palmae) and Dasypogonaceae.

They have woody, hard stems (with fibers and siliceous structures) with a cylindrical shape, well differentiated, with leaves arranged at the ends of them, and with fruits like drupes or berries with 1 or 3 seeds. Small and numerous flowers, panicle-shaped and grouped in spadix or woody spathe.

Asparagales

The asparagales group some 36670 species, and to the families Amaryllidaceae, Asparagaceae, Asphodelaceae, Asteliaceae, Bladfordiaceae, Boryaceae, Doryanthaceae, Hypoxidaceae, Iridaceae, Ixioliriaceae, Lanariaceae, Orchidaceae, Tecophulaeaceae, Xeroemataceae.

These plants can be terrestrial or epiphytic, with leaves arranged in a narrow or open spiral at the base of the plant, at its ends, or along the stem.

Lilies are typical monocots. Source: pixabay.com

Commelinales

They are made up of about 885 species and by the families Commelinaceae, Haemodoraceae, Hanguanaceae, Phylydraceae, Pontederiaceae.

They are plants with perfect flowers with showy petals and differentiated from the petals. The commelinales are pollinated by the wind and by insects. Some are herbs, epiphytes or climbers.

Dioscoreales

This order includes about 844 species and the families Burmanniaceae, Dioscoreaceae, Nartheciaceae.

They are non-mycotrophic plants, they have flowers with septal nectaries. The gynoecium is super or inferior. The leaves can be pinatinervated with petioles. The order Dioscoreales contains climbing plants with thick tubers, spike inflorescences, racemes or panicles.

Many of them are used for nutritional and medicinal purposes, since cortisone is obtained from them.

Liliales

These plants comprise about 1736 species and group the families Alstroemeriaceae, Campynemataceae, Colchicaceae, Corsiaceae, Liliaceae, Melanthiaceae, Petermanniaceae, Philesiaceae, Ripogonaceae and Smilacaceae.

These plants develop petaloid sepals (tepals) in shape and texture. The endosperm is hard, and reserves proteins and hemicellulose, without a mealy consistency. The veins of the leaves are pinnati-parallel.

They are plants that form mycorrhizal association. The leaves can be from linear to parallelinerial.

Wheat and other species of the order Poales are fast growing. Source: pixabay.com

Pandanales

The pandanales have about 1,579 species and comprise the families Cyclanthaceae, Pandanaceae, Stemonaceae, Truiridaceae and Velloziaceae.

They are arborescent plants that inhabit tropical jungles or coastal areas of the tropics. They group from grasses to entwined lianas from the forest floor.

It contains species of which the fibers of the leaves and roots are used to make mats, baskets, twine and nets for fishing. Some species have edible starchy fruits.

Others are used to produce a popular perfume and flavoring in Southeast Asia. Other plants in this order are ornamental as they have very glossy, dark leaves with white or silver margins.

Petrosavials

This is a small order with four species belonging to the Petrosaviaceae family.

Poales

The poales comprise some 23,362 species and the families Bromeliaceae, Cyperaceae, Ecdeiocoleaceae, Eriocaulaceae, Flagellariaceae, Joinvilleaceae, Juncaceae, Mayacaceae, Poaceae, Rapateaceae, Restionaceae, Thurniaceae, Typhaceae and Xyridaceae.

This order includes the most numerous and economically important families such as grasses. The habitat of these plants is terrestrial, although there may also be aquatic ones.

Zingiberales

The Zingiberales order comprises some 2,619 species, and groups together the families Cannaceae, Costaceae, Heliconiaceae, Lowiaceae, Marantaceae, Musaceae, Strelitziaceae and Zingiberaceae.

They are flowering plants with well-developed perianth, whose pollination is carried out by insects or other animals. The sepals of the petals are clearly differentiated. Leaves with pinnate-parallel venation.

Examples of species

Elodea callitrichoides

It is an aquatic plant of the order Alismatales, belonging to the Hydrocharitaceae family. It is used in aquariums. The stem shows the leaves arranged in trimer whorls. The mesophyll is composed of two layers, the stem has opposite leaves and the female flower in the axillary position and is surrounded by a bifid spathe.

The base of the spathe has a long hypanthium with the perianth at its end, with a style of three bifid stigmata.

The ovary is inferior and the male flower shows three sepals wider and shorter than the petals. It has 9 stamens.

Syagrus romanzoffiana

It is a palm tree belonging to the Arecaceae family of the Arecales order. It has a woody spathe, which protects the inflorescence with female and male flowers. They have a trilocular, triovulate ovary and three fused carpels.

It is used as an ornamental, food species, to extract oils, waxes, make soap and palm wine.

Syagrus romanzoffiana is a species in the Arecales order. Source: Forest & Kim Starr

Commelina erecta

It is a plant belonging to the Commeliaceae family of the Commelinales order. It is an ornamental herb for garden or indoor use. It is perennial, leaning and can produce roots at its nodes. It grows up to 1500 meters above sea level.

The stems are about 90 cm, leaves alternate, narrow and ovate, pointed, rounded at the base and with lobes or auricles on the sides. They have an enveloping stem sheath and show pubescence on top of the sheath.

The flowers have three delicate green or white sepals, one of them narrower. The corolla has three petals, two are blue and large, and the other is small, white. The fruit is a globose capsule that is wider towards the apex and the seeds are gray or black.

Commelina erecta can be a weed on some crops as it is not sensitive to glyphosate. Source: Assaf Shtilman

It is a plant reported as a weed in rice and crops such as coffee, sugarcane, and citrus, but it is not a concern; although, as it is not susceptible to the herbicide glyphosate, it can pose a problem in systems of minimum tillage or direct seeding.

Zingiber officinale

This plant is commonly known as ginger. It belongs to the Zingiberaceae family of the Zingiberales order. It is a herbaceous, perennial, rhizomatous plant that can measure 1 m in height.

It has a thick, fleshy rhizome with many knots present. The stems are simple, their leaves lanceolate, oblong, arranged along the stem. The flowers are sessile, yellow in color with purple lips.

The flowers are grouped in a very dense spike at the end of the stem. The part that is used of this plant is the rhizome and it has multiple medicinal and culinary properties. Its flavor is spicy and fresh.

Ginger is one of the representative species of the Zingiberales order. Source: pixabay.com

Alstroemeria aurantiaca

It is a plant belonging to the Alstroemeriaceae family of the Liliales order. It is a flower known as the lily of the Incas or Peruvian lily.

The origin of this plant is in Chile and Peru. It consists of a rhizomatous plant with straight and simple stems, measuring 40 to 80 cm in height.

The leaves are lanceolate and its flowers can be predominantly yellow or orange, but they can present other colors. It is a toxic plant that should not be ingested.

Propagation occurs by division of clumps that form at the base of the mother plant. It is used as an ornamental, and its flower is very commercialized since when the inflorescence is cut, it can last a long time in a vase with water.

Alstroemeria aurantiaca and other astromeliads belong to the order Liliales. Source: Jason Hollinger

Triticum aestivum

This wheat is known as bread wheat and is the most widely cultivated cereal worldwide. It belongs to the Poaceae family of the Poales order.

It is a non-perennial crop that has modified fruits and arranged in a terminal spike. Wheat can be wild or cultivated.

The root can reach up to a meter, the stem is hollow (as in the cane), the leaves are parallel-ribbed, tapered, and end sharply.

The inflorescence is a compound spike that has a central stem known as the rachis, with many internodes and in the middle of them there is a spikelet surrounded by two bracts with a coriaceae texture.

The fruit is a caryopsis with a very important endosperm that contains reserve substances as the main product of the grain.

Vanilla planifolia

Vanilla is a species of orchid, belonging to the Orquidaceae family of the Asparagales order. This plant is marketed for its pleasant aroma and flavor in the cosmetic and confectionery industry.

It is a liana with an epiphytic habit with yellow or greenish flowers. It is known as vanilla since the fruits are shaped like a sword pod. It is a species pollinated mainly by bees, and its fruits are dispersed by bats.

The main substance of vanilla and who gives its essence is vanillin, although there are 150 other compounds or more that provide the fragrance to this plant. It is considered an endangered species in Mexico.

Vanilla is a species of orchid belonging to the Asparagales order. Source: pixabay.com

Dioscorea multiflora

It is a native plant of Brazil, especially in the southern part of this country. It belongs to the Dioscoreales order. The main use of this plant is the production of diosgenin, a substance widely used in the pharmaceutical industry both for the production of cortisone and for substances for contraceptive purposes.

Due to its importance, in vitro propagation studies have been carried out, with effective and useful results for its commercial production, which allow to preserve the species.

Pandanus leram

It is a species belonging to the Pandanaceae family of the Pandanales order. It is an evergreen tree, with edible fruit and other parts also usable by man.

It lives in coastal areas, in temperatures between 22 and 32 ° C. The species does not keep dormant shoots, therefore, when cutting old wood, these shoots do not grow. The pulp of the fruit must be cooked as it contains a harmful substance. The seeds have a delicious nutty flavor and the young leaves are eaten raw.

It has no known medicinal uses, while its leaves are used to make roofs or make mats. The fibers of the drupes are used as a kind of brush to remove dust from the feet.

References

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