Grasses: types, characteristics, examples and their importance in the plant world

What are grasses? Definition and general characteristics

Grasses or Poaceae are a family of monocotyledonous angiosperm plants, mainly herbaceous, although they include woody species (such as bamboos). Its most recognizable feature is the presence of stems called canes, generally cylindrical and hollow, articulated by solid nodes, from which alternate, long, distichous-arranged leaves emerge.

This family comprises approximately 10.000 to 12.000 different species, distributed throughout the world, representing about 20-24% of terrestrial vegetation. Their adaptability allows them to dominate everything from grasslands and savannas to mountainous areas, deserts, aquatic ecosystems, and urban environments.

Main morphological characteristics of grasses:

• Stems or canes: Generally aerial, they can be erect, ascending, creeping (stoloniferous), rhizomatous or even floating.
• Sheets: Alternating arrangement, with a sheath that embraces the stem, a ligule at the junction between the sheath and the blade, and a generally linear blade with parallel venation.
• Inflorescence: Basic unit called spikelet, composed of one or more sessile flowers or flowers seated on an axis (rhachilla), protected by bracts called glumes. The spikelets may be grouped in spikes, racemes, or panicles.
• Flower: Tiny and inconspicuous, without petals, it is usually hermaphrodite and generally has 3 stamens with hanging anthers and anemophilous pollen (carried by the wind), which increases its allergenic potential.
• Fruit: La caryopsis, an indehiscent dry fruit where the seed is fused to the pericarp (example: the grain of wheat or rice).

The basic morphology of grasses includes: stem (culm), elongated leaves (sheath, ligule, blade), spikelet inflorescence and caryopsis fruit.

The morphological structure of grasses has evolved to maximize pollen dispersal and environmental resilience, which is why they dominate vast biomes across the planet.

Taxonomy and classification of Poaceae

The Poaceae, also called Gramineae, belong to the order Poales. They are a family recognized in all botanical classification systems, from Linnaeus to the most modern phylogenetic classifications.

Within the grass family, there are around 800 genera distributed in 13 main subfamilies, among which stand:

• Pooideae: Includes temperate climate cereals such as wheat, barley and oats.
• Panicoideae: It includes corn, sorghum, millet, and tropical grasses.
• Bambusoideae: Bamboos (woody and herbaceous).
• Chloridoideae: Grasses adapted to arid environments, such as gramón (Cynodon).
• Arundinoideae and other less numerous subfamilies.

Thus, grasses are present in almost all ecosystems, highlighting their enormous capacity for adaptation and ecological specialization.

Evolution, distribution and ecology of grasses

The Poaceae are one of the most successful and cosmopolitan families on the planet. Their diversification and evolutionary success is linked to key physiological, morphological and reproductive adaptations, such as:

• Anemophilia: Wind pollination, which allows for the mass production of pollen and the conquest of open spaces.
• Protected basal meristems: They allow regrowth after grazing, fires or cutting.
• Photosynthesis C3 and C4: Some subfamilies possess C4 physiology, efficient in hot and dry climates, which favored their expansion during periods of global climate change.

Grasses dominate prairies, steppes, savannas and grasslands on all continents.. Furthermore, they have shaped landscapes and fauna, as their expansion allowed for the emergence of large herbivorous animals and subsequent human evolution.

On the Iberian Peninsula, the Balearic Islands, and the Mediterranean, grasses are ubiquitous, from beaches, marshes, and dunes to cultivated fields, meadows, cleared forests, and even high mountain areas.

Life cycle and reproduction of grasses

Grasses can be annual, biennial or perennial.

• annuals: They germinate, flower, bear fruit and die in a single vegetative cycle (example: wheat, wild oats).
• Perennials: They live for several years, sprouting each season from the base or from rhizomes/underground (example: fescue, Miscanthus, common reed).

Reproduction is usually sexual, although some species exhibit apomixis (asexual reproduction via seed). In pollination, anemophilous transport predominates, which can cause the famous pollen allergy during flowering periods.

The grass seed, the grain or caryopsis, contains the embryo and the reserves (endosperm), which has allowed its domestication and use as food for millennia.

Flowering season and grass allergies

The pollination period for grasses varies depending on the species and geographical area, although peak pollination usually occurs in spring and early summer. In Mediterranean regions, peak pollen release occurs during the temperate and warm months, coinciding with the simultaneous flowering of many species.

Grass pollen is the main trigger of allergic rhinitis and seasonal asthma in many people, especially in countries with Mediterranean and temperate climates. Symptoms include sneezing, itching of the nose and eyes, watery eyes, nasal congestion, runny nose, and, in severe cases, asthmatic bronchospasm.

Grasses also cause cross-reactivity; that is, if you're allergic to one species, you're likely to react to many others.

Which species cause the most allergies?

• Timothy grass (Phleum pratense)
• Kentucky bluegrass (spikelet)
• Ryegrass (Lolium perenne and Lolium rigidum)
• Common grass (Cynodon dactylon)
• Fescue (Festuca rubra)

Additionally, if you are allergic to grass pollen, there is a slight possibility of cross-reaction with foods such as nuts (almonds, peanuts), melon, kiwi, watermelon, or cherries.

Check local daily pollen levels if you have symptoms and avoid prolonged outdoor exposure during peak pollen season.

Types of grasses: classification by use and biological cycle

Grasses can be classified according to different criteria: consumption (human and animal food), ornamental use, life cycle, size or resistance.

1. Edible or consumption grasses

They include all cereals, grain crops, and livestock feed. They form the basis of the world's food supply.

• Wheat (Triticum)
• Rice (Oryza sativa)
• Corn (zea mays)
• Barley (vulgar hordeum)
• Oats (Avena sativa)
• Rye (Secale cereale)
• Sorghum (Sorghum)
• What's good
• Sugar cane (Saccharum officinarum)
• Edible bamboo (Phyllostachys edulis)

In the (https://www.jardineriaon.com/ornamental-grasses.html) includes many species cultivated for consumption and food production.

2. Forage grasses

They are grown for pasture, hay or silage for ruminant animals or birds.

• Tall fescue (Tall fescue)
• Perennial ryegrass (Perennial ryegrass)
• Elephant grass (Panicum elephantipes)
• Honey grass (paspalum dilatatum)

For proper care, we recommend you consult strategies for pruning grasses in your garden in our grass pruning guide.

3. Ornamental grasses

They are used to decorate gardens, parks, and green spaces. They stand out for their appearance, leaf color, and the spectacular nature of their inflorescences.

• Grass (Kentucky bluegrass, lolium, Festuca, bentgrass)
• Muhlenbergia capillaris: Compact and with intense pink flowers in autumn.
• Imperata cylindrica 'Red Baron': Reddish and shiny leaves.
• Miscanthus sinensis zebrinus: Bicolor variety, green and yellow banded leaves, white flowers in summer.
• Cortaderia selloana (Pampas grass): Large, feathery spikes of landscape value.
• Stipa tenuissima: Fine grass with vaporous movement.
• Festuca glauca (blue fescue): Compact, bluish and very ornamental.
• Pennisetum setaceum (foxtail): Fluffy and attractive inflorescences.
• Hakonechloa macra 'Aureola' (sun pearl): With variegated leaves and arched growth.

For more information on how to care for these species, visit our section on ornamental grasses.

4. Invasive grasses and weeds

Some species have a high colonizing power and can displace native vegetation or hinder crops:

• Aleppo sorghum (Sorghum halepense)
• Gramón (Bermudagrass)
• Lenten grass (Digitaria sanguinalis)
• Brachiaria (Brachiaria extensa)

Before introducing a species into your garden, find out about its characteristics and invasive potential in our article dedicated to ecological tools and methods for weed control.

Main genera and species of grass plants

Some of the most important genres, both in food and in gardening and landscaping, include:

• Triticum: Common wheat (Triticum aestivum), durum wheat (Triticum durum).
• Oryza: Common rice (Oryza sativa), African rice (Oryza glaberrima).
• Zea: Common corn (zea mays).
• Saccharum: Sugar cane (Saccharum officinarum).
• Hordeum: Barley (vulgar hordeum).
• Secale: Rye (Secale cereale).
• Milium: Darling (Milium effusum and others).
• Panicum: Switchgrass (panicum virgatum).
• Phalaris: Birdseed (Phalaris arundinacea).
• Poa: Common grass (Kentucky bluegrass).
• Lolium: Perennial ryegrass (Perennial ryegrass).
• Fescue: Blue fescue (Fescue glauca), festuca gautieri.
• Pennisetum: Foxtail (Eastern Pennisetum, pennisetum setaceum).
• Stipa: Esparto (very tenacious stipa), Stipa tenuissima.
• Arundo: Common reed (arundo donax).
• Cymbopogon: Lemongrass.
• Bambusoideae: Fargesia rufa, Phyllostachys viridis, Phyllostachys aurea (green, golden, black or dwarf bamboo).
• Cortaderia: Pampas grass.
• Deschampsia: Deschampsia cespitosa.
• Eragrostis: Purple lovegrass (Great Grosbeest).

For more information, see our article dedicated to grasses, a powerful family of plants.

Why are grasses so important? Uses and benefits

Grasses are of enormous ecological, economic, food, landscape and industrial importance:

• Human nutrition: More than 50% of the calories consumed worldwide come directly or indirectly from grasses (bread, rice, pasta, cereals, vegetable oils, etc.).
• Animal feed: Forage, hay and feed for cattle, horses, poultry and other domestic animals.
• Gardening and landscaping: Lawns, borders, hedges, windbreaks, modern and naturalized gardens.
• Industry: Use in the manufacture of paper, esparto grass, fibers, musical instruments (reeds), bioethanol, alcoholic beverages, etc.
• Erosion and restoration: Erosion control and soil stabilization in urban and rural environments.
• Environment: They sequester carbon and contribute to the carbon cycle, helping to regulate the global climate.

Care and maintenance of grasses in gardens

Grasses are known for being hardy, low-maintenance, and highly versatile in landscape design. However, they do require some basic care to keep them healthy and attractive all year round:

• Irrigation: Many species are drought-tolerant, but moderate watering during very dry periods improves their vigor. Avoid waterlogging.
• Pruning: Annual pruning in late winter or early spring, cutting old stems almost to ground level.
• Division: Every few years, divide clumps of perennial grasses to rejuvenate the plant and control its spread.
• Fertilization: Generally, light organic fertilizers in spring are sufficient.
• Pest control: They are rarely attacked, but watch out for possible fungal attack, especially in conditions of excessive humidity.

For more information on caring for them, visit our article on .

Environmental Care: Invasive Grasses and Precautions

Some ornamental grasses have become invasive species outside their original habitat, displacing native flora and altering ecosystems. Notable examples are the Pampas grass (Cortaderia Selloana), especially problematic in coastal areas, and the gramón (Bermudagrass).

Before planting or propagating a grass, find out if it's listed as an invasive species or subject to legal restrictions in your area.

We recommend consulting our to maintain an environmental balance.

Examples and details of some notable grasses

We present examples of grasses relevant to gardening, landscaping and agriculture:

1. Miscanthus sinensis: Up to 2 meters tall. Flowers in large tufts, green leaves edged with white or yellow.
2. Cortaderia selloana (Pampas grass): White or pink feathery spikes, ornamental, invasive in some areas.
3. Muhlenbergia capillaris: Pink clump in autumn, ideal for borders.
4. Imperata cylindrica 'Red Baron': Color changes from green to red throughout the year, very decorative.
5. Pennisetum setaceum: Pink, purple or white brush-like inflorescences.
6. Stipa tenuissima: Thin and flexible leaves, vaporous effect.
7. Festuca glauca: Compact blue bush, ideal in rockeries.
8. Panicum virgatum: Perennial switchgrass, adaptable and drought resistant.
9. Arundo donax: Common reed, widely used in environmental restoration and construction.
10. Phleum pratense: Timothy grass, forage, one of the most allergenic pollens.

Comparison: grasses vs. other similar herbaceous plants

In gardens and green spaces, grasses can be confused with the families of Cyperaceae and Juncaceae, but there are key differences:

• Grasses: Cylindrical and hollow stems, leaves with ligules, spikelet inflorescence.
• Cyperaceae: Stems generally triangular, solid, without ligule or open sheath, spike-shaped inflorescence, but more rigid appearance.
• Juncaceae: Solid, cylindrical stems, cylindrical leaves, small flowers without showy bracts.

For more details, see our section on .

Reproduction, pollination and dispersal

The vast majority of grasses have hermaphrodite flowers, although there are monoecious and dioecious species. Wind pollination increases the amount of pollen suspended in the air. Seed dispersal can occur by wind, water, or by animals carrying fruit attached to their fur.

To expand your knowledge, check out our article on .

Diversity, genetics and adaptability of grasses

The evolutionary success of the Poaceae is a result of their enormous genetic variability, phenotypic plasticity and frequent polyploidy. The size and content of their genomes vary greatly (the rice genome is 11 times smaller than that of barley). Most species are polyploid, which has allowed them to adapt to extreme environments.

Grasses have generated mutualistic associations with fungi (mycorrhizae and endophytes) and nitrogen-fixing bacteria, which contributes to the improvement and sustainability of the ecosystems where they coexist.

Grasses and climate change: ecological role

Grass-dominated grasslands are one of the main terrestrial carbon sinks. Through photosynthesis, they fix enormous amounts of atmospheric carbon, stabilize soils, and regulate the microclimate, humidity, and temperature of the regions where they thrive, playing a crucial role in maintaining biodiversity.

In the context of climate change, its cultivation and sustainable management are essential for the resilience of ecosystems and the world's food supply.