GRASSES: CHARACTERISTICS, HABITAT, REPRODUCTION, USES - BIOLOGY - 2025

The grasses (Poaceae) are a family of herbaceous plants, occasionally woody belonging to the order Poales of the group of monocots. This family is made up of more than 850 genera and approximately 12,000 identified species, which constitutes the fourth family with the greatest biodiversity.

This family is made up of a great diversity of cosmopolitan species, which are located in a wide range of ecosystems; grasses are found in deserts, marine environments, flooded lands, mountainous areas, jungles, and icy environments.

Wheat is one of the main grasses cultivated worldwide. Source: pixabay.com

The extraordinary adaptation of grasses to different environments is due to their physiological, morphological, reproductive variability and broad symbiotic relationships with other species. In fact, this great variability makes grasses one of the plant families of greatest economic importance and biological diversity.

Without a doubt, grasses represent the largest percentage of the daily diet of humans. Directly as grains, flours, oils or their derivatives; and indirectly as meat, milk or eggs from cattle that feed on forage and grains.

Among the commercial species of grasses, rice (Oryza sativa L.), wheat (Triticum aestivum L.) and corn (Zea mays L.) stand out. As well as oats (Avena sativa L.), sugar cane (Saccharum officinarum), sorghum (Sorghum spp.), Rye (Secale cereale L.), barley (Hordeum vulgare L.) and bamboo (Subf. Bambusoideae)

General characteristics

Habits

Most grasses are annual or perennial grasses, a few centimeters long and creeping, up to large woody bamboos 30 m high. In these species copiously branched rhizomes and unbranched stems are common, with abundant solid or hollow nodes inside.

Leaves

The leaves are alternate and paired, formed by a basal sheath, a ligule and a lamina; they also lack stipules. The basal sheath has free margins and the base forms a fused tube that surrounds the stem and alternate leaf sheaths.

The flattened or folded blades separate from the stem at the tip of the sheath, sometimes forming a pseudopeciole at the base. The ligule is always present, with cells that store silica and of membranous forms or a simple hairy strip.

Saccharum officinarum. Source: B.navez

Inflorescences

The compound inflorescences are forming a central unit or spikelet, arranged in panicles, racemes, spikes or other arrangement. It contains even bracts, at the base of the spikelets a pair of glumes, and under each flower another pair, the lemma and the palea.

flowers

The flowers are unisexual and bisexual, with 3-6 stable free and filamentous, and large anthers, super-ovaries and branched estimates.

Fruit

The fruit is a caryopsis, indehiscent with thin walls, with the pericarp consistently fused and covering a solitary seed.

Seeds

There is one unit per fruit, the embryo has a scutellum and the endosperm is mainly starch.

Habitat and distribution

Grasses are a cosmopolitan group of species that are found in all types of ecosystems, from xerophilous to aquatic environments. Indeed, the poaceae or grasses constitute approximately 24% of the vegetal kingdom that covers the Earth.

These species are common in the grasslands of South America, the grasslands of North America, the steppes of Eurasia, and the savannas of Africa. Grass species has even been identified in Antarctica.

Rice cultivation. Source: pixabay.com

Taxonomy and subfamilies

- Kingdom: Plantae

- Division: Magnoliophyta

- Class: Liliopsida

- Subclass: Commelinidae

- Order: Poales

- Family: Poaceae Barnhart

Synonyms

- Family: Gramineae Juss., Nom. cons.

Subfamilies

The main characteristics of the subfamilies of grasses and some representative examples are described below.

Anomochlooideae

Herbaceous plants with a particular inflorescence formed by a pseudopeciole, the ligule transformed into a hairy tuft and the inflorescences grouped in cymes. This subfamily is distributed from Central America to Brazil and includes four species of the Anomochloa and Streptochaeta genera.

Aristidoideae

Type C ⁴ plants with edges along the basal column native to temperate and warm climates. It comprises 3 genera and more than 300 species, being the genera Aristida and Stipagrostis the best known.

Arundinoideae

It is made up of xerophytic and hydrophytic plants whose habitat is located in tropical or temperate zones. It comprises 14 genera and more than 20 species, among which are the Arundo donax (Castile cane) species and the Phragmites genus.

Bambusoideae

Commonly known as bamboo, this group is made up of mostly herbaceous and woody species of tropical distribution. Among the woody bamboo genera are Arundinaria, Bambusa, Chusquea, Phyllostachys and Sasa.

Bamboo. Source: pixabay.com

Centothecoideae

Subfamily consisting of 11 genera and 30 natural species from the tropics and warm temperate forests. They are characterized by the style present in each flower and the presence of epiblast during the development of the embryo.

Chloridoideae

The plants of this group have spikelets that separate on the glumes and slightly pubescent leaves, being C ⁴ plants. They are distributed in semi-arid and arid tropical areas, mainly in Australia and Africa.

Representative genera of the subfamily include Chloris, Eragrostis, Eustachys, Muhlenbergia, Spartina, and Sporobolus.

Danthonioideae

A cosmopolitan group of grasses that have bilobed prophylaxis or bracteoles and the synergistic cells of the embryo sac are haustorial in shape. It is made up of 19 genera and more than 270 species, including the Danthonia and Rytidosperma genera, being the grasshopper (Cortaderia Selloana) an ornamental.

Ehrhartoideae

This group is characterized by inflorescences with the androecium of six stamens and spikelets with very small glumes. Among its representatives is the common rice (Oryza sativa) native to Asia, in addition to 21 genera and 111 species of botanical interest.

Micrairoideae

Monophyletic subfamily whose members have dome-shaped stomata, hairy ligules, small embryos, endosperm with simple starch grains, and C ⁴ photosynthesis. This group of tropical origin is made up of 8 genera and more than 170 species, which includes the genera Eriachne, Isachne and Micraira.

Panicoideae

Subfamily that differs by its dorsally compressed spikelets lacking rachillae and with two flowers, likewise they are C ⁴ plants. They are species of tropical habits, comprising more than 200 genera and 3,600 species, and includes the genera Andropogon, Paspalum, Panicum, Setaria, Sorghum (sorghum) and Zea (corn).

Sorghum. Source: pixabay.com

Pharoideae

These plants are characterized by resupinate leaves and unifloral spikelets with six stamens with centrixed anthers. This pantropical distribution group is made up of four genera and about twelve described species.

Pooideae

It comprises the most numerous subfamily of grasses, with more than 195 genera and 4,200 species. Pooideae are distributed around the globe throughout tropical regions.

Its particular characteristic is that the branches of the inflorescences are paired and the lemma has five nerves. Representative crops include oats, wheat, barley and rye, as well as hay, grass, forage crops and some weed species.

Puelioideae

This subfamily is characterized by its gynaeceans with double stigmas and spikelets that disintegrate on the glumes when mature and its androecium of six stamens. This group distributed throughout tropical Africa is made up of eleven species belonging to the Guaduella and Puelia genera.

Reproduction

Most grasses are hermaphrodite and alogamous plants, that is, they reproduce by cross fertilization and their pollination is anemophilic or by the wind. However, there are various reproductive processes that occur in such a large family, which are described below.

Self-compatibility

Self-fertilization and self-pollination mechanisms are frequent in grasses, mainly in colonizing species with an annual cycle. An average of 45 species display this mechanism, among which we can mention Avena, Agropyron, Lolium, Oryza, Secale and Triticum.

Self-incompatibility

Self-incompatibility in grasses occurs when a hermaphroditic plant is unable to produce seeds if its stigmas are pollinated by its own pollen. This type of gametophytic incompatibility is due to the interrelation of the independent "SZ" genes with various alleles.

The consequence of self-incompatibility is that no seeds are produced, but it favors genetic variability. Among the main genera of the Poaceae family that present self-incompatibility are Dactylis, Festuca, Hordeum, Lolium and Secale.

Lolium multiflorum. Source: Matt Lavin from Bozeman, Montana, USA

Apomixis

The mechanism of apomixis in grasses is related to asexual reproduction through seeds. In this regard, embryos from a non-reduced oosphere develop by mitosis without fertilization taking place.

This type of reproduction, where each new embryo is genetically identical to the mother plant, is particular to the Andropogóneas and Paníceas. Of the most representative genera are Apluda, Bothriochloa, Capillipedium, Cenchrus, Dichanthium, Heteropogon, Setaria, Sorghum, Paspalum and Themeda.

Dioecia

Dioecious plants, where male and female plants occur independently, are rare in grasses. Only 18 genera are dioecious, Poa being the most representative, even the dioecious species of Poa belong to the subgenus Dioicopoa.

Gynodioecia

This mechanism is based on the natural coexistence of female individuals and hermaphrodites of the same species. Despite being uncommon in grasses, some species of the subgenus Poa, Cortaderia, and the species Bouteloua chondrosioides are gynodioic.

Monoecia

This mechanism is characterized by the presence of both sexes on the same plant but separately. In monoecious plants, the presence of male and female inflorescences on the same plant is common.

Monoecious are the genera Ekmanochloa, Humbertochloa, Mniochloa, Luziola and Zea. A frequent condition in this mechanism is the andromonoic species where the two sexes are located in spikelets of different heterogamous pairs.

The andromonoic mechanism is present in the Andropogóneas and Paníceas, being some representative genera Alloteropsis, Brachiaria and Cenchrus. As well as Melinis, Echinochloa, Oplismenus, Setaria, Panicum, Whiteochloa and Xyochlaena.

Applications

Nutritional

The grain or caryopsis of grasses is part of the daily diet of the world's population, both in direct form or ground as flour. In fact, rice (Oryza sativa), corn (Zea mays) and wheat (Triticum aestivum and T. durum) are the main grasses for human consumption.

Likewise, other grasses cultivated as a food source or food additive are oats, barley, rye, millet, sorghum and sugar cane. On the other hand, grasses are an important source of nutritional supplements for different types of livestock: cattle, goats, pigs, among others.

Corn (Zea mays). Source: pixabay.com

Among the main forage grasses we can mention: Avena fatua, Agropyron elongatum, Brachiaria brizantha, Bromus unioloides, Cynodon nlemfuensis or Eragrostis curvula. As well as: Festuca arundinacea, Lolium perenne, Panicum elephantypes, Panicum maximum, Panicum miliaceum, Pennisetum americanum, Phalarisa rundinacea, Phleum pratense, Phalaris tuberosa.

Industrial

Species such as Lygeum spartum and Stipa tenacissima are used to make handmade baskets and esparto slippers or natural fiber espadrilles. A rudimentary type of broom is made from Sorghum technicum fibers, and Stipa tenacissima is used to make scourers.

Handcrafted brushes are made with the strong and rigid fibers of Aristida pallens and Epicampes microura. Likewise, with the fibrous and dry reed of certain grasses, such as bamboo, musical instruments such as the flute are made.

Bamboo fiber is used to make paper, and the pulp is a raw material for plywood or rayon fabric. The thick and resistant stems are used in construction and decoration, and the fiber of some species of bamboo is used to make furniture.

The lemongrass (Cymbopogon citratus) is a poaceae from which an oil called citronella is extracted, widely used in perfumery. Barley (Hordeum vulgare) is a basic ingredient for making malt and beer, among other liqueurs such as rum, gin, vodka, and whiskey.

From rice (Oryza sativa) a traditional Japanese drink called "sake" is made. On the other hand, corn (Zea mays) produces a high quality edible oil and ethanol used as fuel.

Grass

A small group of grasses are tussock species, that is, species with short rhizome, dense growth and resistant to trampling. Of the grasses used as grass are the genera Axonopus, Festuca, Lolium, Paspalum, Poa and Stenotaphrum.

The tussock species are herbaceous and stoloniferous poaceae used to cover patios, parks, gardens, fields and sports fields. Being particular the characteristics of Agrostis palustris used to cover the "green" on golf courses.

Agrostis stolonifera. Source: Matt Lavin from Bozeman, Montana, USA

Ornamental

Tall grasses such as bamboo (Arundinaria) are used as shading barriers, or Cortaderías are ideal to cover grass meadows. In gardening, Festuca and Hordeum are used for their bluish leaves and dense foliage to upholster rockery or rocky areas.

Similarly, the Lagurus or spike flower breeze is sown in a specific way, or combined with the Phalaris. This gives a good contrast of low, dense foliage with large feathery spikes, or Pennisetum can be used.

Conservation

Some grasses such as vetiver (Chrysopogon zizanioides) are used to control damage caused by erosion, prevent landslides or to fix dunes.

Medicinal

Some species such as Cynodon dactylon and Elymus repens are used in traditional medicine as a diuretic.

References

1. Giraldo-Cañas, Diego. (2010). Ornamental grasses (Poaceae) used in handicrafts in Colombia. Polybotany, (30), 163-191.
2. Herrera, Y., & Peterson, PM (2013). Poaceae. Mexican aquatic plants: a contribution to the flora of Mexico.
3. Poaceae. (2019). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
4. Poaceae Barnhart - Gramineae Juss. (nom. alt.) (2017) Systematics of Vascular Plants. Recovered at: thecompositaehut.com
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6. Valdés Reyna, J., & Davila, PD (1995). Classification of the genera of Mexican grasses (Poaceae). Acta Botánica Mexicana, (33).
7. Vigosa-Mercado, José Luis (2016) Flora de Guerrero Nº. 67: Arundinoideae, Micrairoideae and Pharoideae (Poaceae) 1st edition. Mexico, DF: National Autonomous University of Mexico, Faculty of Sciences. 36 pp.
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