ORCHIDS: CHARACTERISTICS, HABITAT, TYPES, CULTIVATION - BIOLOGY - 2025

The orchids (Orchidaceae) are a group of herbaceous flowering plants belonging to the family of the Asparagales Orchidaceae order. In this regard, these monocotyledonous plants are characterized by the diversity of their flowers and their ecological interactions with other species.

This family includes between 25,000-30,000 species, which constitutes one of the taxonomic groups with the highest specific diversity among angiosperms. In addition to this great natural variety, more than 60,000 hybrids and cultivars genetically improved by farmers are added.

The Cattleya is one of the best known orchids. Source: pixabay.com

The great morphological variety of orchids makes possible the presence of specimens of a few centimeters up to species of more than three meters in height. This great diversity is also present in the size, shape, color and aroma of its flowers.

They are usually located in tropical climates, but nevertheless, their distribution is global, with the exception of desert and polar environments. In fact, they are cosmopolitan species widely established in the wild or commercially in intertropical climates where the most attractive species are cultivated.

Most of its species have epiphytic growth habits with smooth and slightly thickened roots. On the other hand, there are the semi-epiphytes, which adhere to a porous material, and the terrestrial ones that maintain symbiotic relationships with the mycorrhiza.

Its flowers are arranged alone or in bouquets of brightly colored inflorescences, generally being hermaphrodite. The distinctive character of orchids is a modified petal called the lip that allows the members of this taxonomic family to be identified.

At present the cultivation of orchids constitutes an important branch of the production of ornamental plants. However, the illegal trade in the vast majority of wild species involves more than 10 million plants a year.

General characteristics

Root

The roots of the orchids present a great differentiation in relation to the habits of life and growth. Terrestrial or rupicolous plants have pubescent roots, whereas epiphytes are thin or thick, smooth and expand horizontally. Some have pseudobulbs.

Stems

Orchids develop a specialized type of stem called a pseudobulb, which acts as a storage organism for water and nutrients. Also, they are characterized by their bulging internodes from which the leaves emerge.

Leaves

The leaves alternately located along the stems have parallel veins across their surface. They are generally lanceolate and have an obtuse apex; thick, firm and leathery, or soft, thin and folded.

Different types of Orchid leaves. Source: Toapel

flowers

The flowers are the distinctive organs of these species, being of very varied sizes from just a few mm to 45-50 cm in diameter. Most are bicolor and sometimes tricolor, in some cases with pints and strong fragrances to attract pollinating insects.

The arrangement of the flowers at the end of the pedicel is resupinate, that is, the flower shows a torsion in its central axis, directing the lip downwards. In addition, they are aligned individually or in groups in spikes, clusters, panicles or corymbs.

Flowering naturally occurs once a year, often during the same time. Thus, flowering is determined by various environmental factors such as changes in temperature, solar radiation, variations in environmental humidity and change in the climatic season.

Taxonomy

The Orchidaceae family is one of the largest groups in the plant kingdom, encompassing around 30,000 species of 900 described genera. These genera are distributed globally on all continents, being more abundant in hot and humid tropical areas.

- Kingdom: Plantae.

- Subkingdom: Tracheobionta.

- Division: Magnoliophyta.

- Class: Liliopsida.

- Order: Asparagales.

- Family: Orchidaceae Juss., Nom. cons.

-Subfamilies

- Apostasioideae.

- Cypripedioideae.

- Epidendroideae.

- Orchidoideae.

- Vanilloideae.

-Description of the subfamilies

The taxonomic classification of the Orchidaceae includes five subfamilies which are described below.

Apostasioideae

The species of this subfamily are characterized by having two or three fertile anthers and a filamentous staminodium. They are considered the most primitive orchids, being native to the Asian and Australian tropics, and include the genera Apostasia and Neuwiedia.

Cypripedioideae

The flowers have two stamens, two fertile anthers, a shield-shaped staminode and another sacciform. They are distributed throughout the American, Asian and Australian tropics, and include the genera Cypripedium, Mexipedium, Selenipedium, Phragmipedium, and Paphiopedilum.

Selenipedium palmifolium. Source: Roberto Takase

Epidendroideae

Subfamily of epiphytic species of flowers with incumbent or curved anthers on the apex of the column, rigid, waxy and cartilaginous. It is considered a very numerous subfamily with more than 500 genera distributed in the Neottieae, Tropidideae, Palmorchideae and Xerorchideae tribes.

Orchidoideae

Most of the species of this subfamily have terrestrial habits, so they have fleshy rhizomes or tubers. The flowers have a fertile anther, and a stamen, comprising more than 200 genera of the Cranichideae tribe.

Vanilloideae

It includes 15 genera and more than 180 species of orchids corresponding to the Pogonieae and Vanilleae tribes. Its distribution is homogeneous throughout the subtropical and humid tropical strip around the globe.

-Etymology

The word "orchid" derives from the Greek "orchis", which means testicle due to the shape of the underground tubers in some species. In fact, the name "orchis" was first used by the father of botany and ecology Theophrastus in his book "De historia Plantarum".

Habitat and distribution

Orchids are perennial plants of herbaceous consistency, epiphytic or terrestrial, sometimes climbing, saprophytic or mycoheterotrophic «parasitic». This family constitutes the largest taxonomic group of flowering plants, including 900 genera with more than 30,000 species of great biological diversity and geographic distribution.

Indeed, it is a cosmopolitan family, the places of greatest diversity being the geographic regions that include Brazil, Borneo, Colombia, Java, New Guinea and Mexico. They are usually located from sea level to 5,000 meters above sea level, with the poles and deserts being the only places where they do not reproduce.

Its geographical distribution is pantropical, covering a strip within 20º north and south latitude of the equator. In Latin America the greatest diversity is located in the high mountains of Colombia, Costa Rica and Panama.

Types

Epiphytic orchids

They are those species that do not require direct contact of their roots with the earth or other humid environment to get their food. In fact, they live on the air, from which they take nitrogen and other minerals through green leaves and roots. Of this group are the Vandas and the Renantheras.

Semi-epiphytic orchids

Orchid species that need to be attached to a woody or porous material that conserves moisture, which does not necessarily have to be earth. These types of plants obtain their nutrients through the aerial roots and through the leaves through the photosynthetic process.

Semi-epiphytic orchids tend to die if placed on the ground, as their roots require continuous aeration to maintain their functionality. From this group the Cattleyas, Oncidium and Laelias live attached to logs or planted in containers with suitable materials.

Some species require high humidity in their substrate, being sown on loose topsoil, with sticks or fern roots. Sometimes sphagnum or coconut fiber is used; among these species are the Miltonias, Phalaenopsis and Cypripedium.

Only Cymbidiums tolerate some black soil in the growing medium. In effect, these are evergreen orchids grown in pots and for marketing as cut flowers.

Terrestrial or rock orchids

They constitute that group of orchids that need to be planted in ordinary soil to obtain water and nutrients from the substrate. Most of the European orchids from the Andean cold zones belong to this group, such as the Lycastes and Sobralias.

Representative species

Cattleya

Cattleya is a genus of Orchidaceae made up of approximately 65 species native to intermediate and high regions of South America and Central America. Most grow epiphytes on the fringes of forests or on treetops, where they are protected from direct sunlight.

Cattleya quadricolor. Source: snotch from Sapporo, Hokkaido, Japan

They are characterized by the thick and fleshy roots with superficial growth, as well as pseudobulbs used as reserve organs. Because of their attractive flowers they are called the "queens of the orchids" due to their attractive colors and pleasant fragrance.

Coelogyne

Coelogyne is a group of epiphytic orchids with more than 195 species native to lowlands and high mountains in warm tropical climates. They are characterized by their inflorescences with large delicate and fragrant flowers of bright colors and particular shapes.

Coelogyne lawrenceana. Source: Dalton Holland Baptista

The species of this family thrive in a wide range of climates, from cool, low-temperature areas to warm areas. Indeed, the floral clusters of white, green or yellow flowers emerge from the buds during spring and summer.

Cymbidium

The orchids belonging to the genus Cymbidium are mostly hybrid species that develop small flowers of great beauty. Natives of Asia, specifically from the Himalayan region, the group is made up of around 52 taxonomically identified species.

Cymbidium iridioides. Source: Michael Wolf

It is a very demanding plant in humidity and does not tolerate direct exposure to solar radiation. They are commonly used as cut flowers for flower arrangements, due to their small flowers, attractive colors and long-lasting fragrance.

Dendrobium

The Dendrobium is one of the most cultivated and commercialized orchids made from artificial crosses to obtain flowers of great variety and beauty. This genus comprises about 1,200 species native to Asia and Australia.

Dendrobium farmeri. Source: Amruth

The qualifier Dendrobium means "the one who lives in a tree" and refers to the frequent habitat of the genus on trees or rocks. The great variety of Dendrobium species, hybrid or natural, have a wide diversity of shapes and colors.

Epidendrum

The genus Epidendrum includes approximately 365 species of great taxonomic diversity that previously included the genera Encyclia, Osterdella, Psychilus, and Nanodes. The largest variety of Epidendrum is native to Mesoamerica, from southern Florida, Central America, South America, to northern Argentina.

Epidendrum baumannianum. Source: Dick Culbert from Gibsons, BC, Canada

This genus tolerates a wide range of temperatures, from very hot and dry climates, to the coldest and most humid ones. The inflorescences are characterized by their long bouquet of tiny colorful flowers and decorative shapes.

Miltonia

A genus of orchids native to Brazil formed by a diversity of species that grow singly or in clusters. Most of the species are adapted to the hot and humid climates characteristic of the Amazon rainforests.

Miltonia cuneata. Source: Dalton Holland Baptista

The flowers of good size exceed 10 cm in diameter, sepals and petals are the same size and the lip differs in color. The pseudobulbs develop on the rhizome and have oblong, linear and flexible leaves of perennial condition.

Oncidium

Group of orchids of a great variety of natural dimensions from tropical America, from the south of Florida to the north of Argentina. The group is made up of approximately 330 species that grow from sea level to 3,500-4,000 meters above sea level.

Oncidium alexandrae. Source: Eric in SF

Flowers come in a wide variety of shapes, sizes, and colors. In fact, hybrids of this genus are highly resistant and can be grown in hanging pots.

Phalaenopsis

Known as “butterfly orchids” they comprise around 60 taxa described and classified as belonging to the Epidendroideae subfamily. The characteristic flowers of Phalaenopsis resemble a butterfly in flight, being highly resistant, and adapting to various environmental conditions.

Phalaenopsis stuartiana. Source: Elena Gaillard from New York, USA

Native to Southeast Asia, they grow wild in Australia and Papua New Guinea. There, they develop naturally on rocky areas, rocks and trees.

Vanda

The Vandas constitute a group of epiphytic or lithophytic orchids of approximately 60 species native to the Asian tropics but distributed globally. In nature they are located under the canopies of large trees protected from direct exposure to sunlight.

Vanda blushes. Source: Greg Steenbeeke

The inflorescences develop at the end of a long stem, making them ideal for growing in hanging pots or on trees. This variety requires abundant irrigation and medium shade, being particular its flowers of pastel tones with spots of light tones.

Cultivation and care

-Culture

The propagation of orchids can be done by seeds and through division or fragments of the stem. Seed production is not commercially viable, and is used only at the laboratory level for the production of new species.

Vegetative propagation is the most used technique and in the case of orchids it is done through the division of the stem. Likewise, depending on the species, it can also be done through suckers that develop from the pseudobulbs.

The commercial cultivation of orchids is generally done in special containers that promote aeration of their roots and good drainage. When placing the stem or sucker fragment inside the container, it is recommended to fix it with a wire that provides support until the roots develop.

-Care

Substratum

Cultivated orchids require a well-draining substrate, adequate porosity, and excellent moisture retention. Ideal substrates are those that provide aeration and moisture, such as driftwood, fern roots, fir bark, or coconut coir.

The roots of this crop are susceptible to the accumulation of water. In addition, a loose substrate favors the growth and development of the root system.

illumination

In general, orchids require 12-14 hours of lighting a day, at an average temperature of 18-25º C, never less than 15º C. In tropical areas the light intensity remains relatively stable throughout the year, therefore that the crop requirements are met.

Crops in areas with fewer hours of solar radiation require a light supplement during the winter months. It is advisable to arrange the hanging pots facing east or south, to take advantage of the greater incidence of light.

Cattleya percivaliana. Source: Orchi

Irrigation

Orchids withstand drought better than excess humidity, and a crop with frequent watering tends to show root rot. As a general rule, an orchid plant should be watered once a week, avoiding waterlogging of the roots.

The type of substrate is of vital importance to maintain the humidity of the growing medium without accumulating water on the roots. A loose substrate that facilitates aeration of the roots will prevent the plant from suffocating and dying.

RH

In tropical conditions orchids thrive effectively with a relative humidity of around 60-80%. During winter or in very dry environments, the relative humidity decreases, so it is advisable to use humidifiers that maintain the ambient conditions.

Fertilization

The suitable substrates for orchids often provide few nutrients, so it is important to provide fertilizers to the crop. In this regard, the application of liquid fertilizers is common in the cultivation of orchids.

Fertilization is carried out when the plants are in active growth or before starting the flowering period. Fertilization is not recommended during winter, or immediately after transplanting.

For most cultivated orchids it is recommended to apply a foliar fertilizer with a higher nitrogen content that favors flowering. Likewise, organic fertilizers are recommended, such as extracts of algae or bioles, which provide macro and micronutrients.

Pruning

Sanitation and maintenance pruning are recommended to keep plants healthy and increase and improve flowering. When dry or diseased leaves or flowers are observed, they are cut above the lower bud so that a new one later sprouts with greater vigor.

Plagues and diseases

-Pest

Red spider mite (Tetranychus urticae)

The highest incidence occurs in environments with low humidity, with abundant colonies being observed on the surface of the cobweb-covered leaves. The damage is caused by the bite of the insect when sucking the sap, causing chlorotic spots that later turn whitish.

The control is carried out with agronomic management increasing the relative humidity of the environment. In severe attacks, sulfur-based chemicals can be used. Likewise, the biological control with Phytoseiulus persimilis is effective.

Mealybugs

Passive whitish insects that affect the back of the leaves. They occur in dry and warm environments, causing yellowish spots on the leaves. Its incidence is accompanied by the attack of the bold fungus, and for its control the application of systemic insecticides is recommended.

Aphid (Aphis fabae)

Aphids are small insects that attack young shoots, leaves and flower buds by sucking the sap and transmitting toxins. The main symptom is the deformation of the affected tissues. In addition, the wounds caused by this plague are a gateway for viruses.

Aphis fabae. Source: Sascha Kohlmann from Berlin, Deutschland

Biological control is recommended with some predators such as Chrysopa or Coccinella septempunctata, as well as the parasitoid Aphelimus mali. In severe attacks, chemical control with systemic insecticides is suggested.

Trips

The incidence of this pest causes whitish spots on leaden-looking buds, leaves and flowers surrounded by black grains. The attack on the flower buds causes the flower to fall or its deformation.

The control can be carried out by applying preventive measures such as the use of antitrip nets, weed control or sticky traps. Likewise, for greenhouse crops, biological control with the Orius or Amblyseius swirskii parasitoids is recommended.

-Diseases

Pythium

This fungus caused soft rot of the roots. The plant fails to absorb water and nutrients, resulting in a general weakening. Preventive measures that include disinfection of the substrate, healthy plant material and controlled irrigation are recommended; chemical control is effective in severe attacks.

Cercospora and Rhizoctonia

Disease of greater incidence in stems and leaves, causing necrotic lesions that decrease the photosynthetic capacity and cause the death of the plant. Preventive measures such as sanitation pruning, controlled irrigation and the use of healthy plant material reduce its incidence.

Chemical control is appropriate when the disease has been strongly established on the crop. Likewise, biological control can be used through applications of Trichoderma harzianum on the substrate.

Pseudomonas cattleyae

Bacteria that affect a large number of orchid species, especially the Phalaenopsis genus, causing the disease known as "brown spot". The highest incidence occurs in humid environments, with low temperatures and poor ventilation.

Its control is carried out by applying preventive measures such as the elimination of infected plant material and facilitating good ventilation. Chemical control is recommended in highly contaminated crops, applying controlled fumigations of antibiotics.

Epidendrum ilense. Source: Averater

Physiopathies

Physiopathies are physiological alterations of the plant caused by external environmental or physical factors. In this regard, sudden changes in lighting, temperature, relative humidity, rainfall or accumulation of ethylene in the leaves influence the health of the crop.

As a consequence of these environmental alterations, the leaves turn yellowish or may present burns. In addition, defoliation and adverse changes of the root system occur, resulting in weak plants with little growth and less frequency of flowering.

References

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