Orchidaceae

Orchidaceae, sometimes known as the orchid family, is a large and diversified group of flowering plants with brightly coloured and fragrant blossoms. They are one of the two largest flowering plant families, along with the Asteraceae. There are around 28,000 currently recognised species in the Orchidaceae, which are divided into 763 genera. Because confirmed data on the members of such massive families is always in flux, determining which family is the largest is still up for contention. Regardless, there are nearly as many orchid species as bony fishes, more than twice as many bird species, and nearly four times as many mammal species.

About 6–11 per cent of all seed plants belong to this family. Bulbophyllum (2,000 species), Epidendrum (1,500 species), Dendrobium (1,400 species), and Pleurothallis (1,400 species) are the largest genera (1,000 species). Vanilla (the vanilla plant’s genus), Orchis (the type genus), and several regularly grown plants including Phalaenopsis and Cattleya are also included. Furthermore, horticulturists have created over 100,000 hybrids and cultivars since the introduction of tropical species into cultivation in the 19th century.

Vegetative Characteristics 

Habit and habitat

• They are perennial and terrestrial.
• They are mostly epiphytic, some are saprophytic and derive their nutrition from the humus as their roots or rhizomes are associated with endoscopic mycorrhiza.
• A few are climbers (Eg. Bulbophyllum)

Root

• The main root is absent. Adventitious roots are present in place of main roots. 
• Roots can be tuberous, fleshy, climbing or aerial.
• Tuberous roots serve for the storage of reserve food material.
• Aerial roots contain epidermis which is specially developed to form a special water-absorbing tissue.

Stem 

• Generally erect 
• Sometimes climbing or trailing
• Generally thickened into rhizome and pseudobulbs (Eg. Bulbophyllum)

Leaf 

• Orchids generally have simple leaves with parallel veins as seen in monocots, only a few have reticulate venation (Eg. Vanilloideae)
• Leaves are usually alternate, sometimes opposite or whorled. 
• Leaves are often distichous, sometimes terete or canaliculate, glabrous or very rarely hairy, frequently fleshy or leathery, base almost always sheathing, sometimes articulated.

Floral Characteristics 

Inflorescence

• Racemose inflorescence, spike or panicles. 
• Inflorescence basal, lateral or terminal. 
• Erect to pendulous.

Flower

• Flowers are of variable and Peculiar shape.
• Often quite showy, usually zygomorphic very rarely actinomorphic.
• Usually bisexual (hermaphrodite), sensible or pedicellate.
• Most often ruspinate with pedicel and ovary twisted through 180 degrees.

Perianth

• Tepals are six in two whorls of each. The outer three tepals are green (calyx) and the inner three tepals are coloured (corolla). 
• The labellum is posterior but comes to life on the anterior side due to twisting of the inferior ovary through 180 degrees.
• Sepals are usually free but sometimes variously adnate.
• Petals are free but rarely partly adnate to sepals.

Androecium

• Usually, three unite with the pistil to form a column opposite to the labellum and act as functional.
• Sometimes two stamens, bithecous, introrse. 
• Pollen is granular or coherent in each cell into one.
• Beak-like sterile stigma makes a connection between ovary and stamen.
• Sometimes staminodes are also present.

Gynoecium

• Tricarpellary, syncarpous
• Ovary inferior, unilocular
• Parietal placentation or rarely 3-locular and axile placentation.
• Usually, there are three stigmas, two lateral ones are often fertile, and the third one is sterile.
• Sometimes all the three stigmas are functional ( Eg. Cypripedium and Paphiopedilum)

Fruit

• In the form of a capsule that is descended by three or six longitudinal slits and remains closed at both ends.

Seed

• Non-endospermic, lightweight and small.

Pollination

• Occurs with the help of insects- entomophilous.

Distribution of Orchidaceae 

• The orchid family (Orchidaceae) is the second-largest flowering plant family, with approximately 763 genera and about 28,000 species distributed nearly worldwide. 
• 130 genera and over 800 species are present in India.
• The family is widely distributed in the tropical and temperate regions of the world.
• In India, it is mainly present in the regions of the eastern Himalayas.

Economic importance of Orchidaceae 

• The Orchidaceae family is of less importance. But the tuberous roots of Habenaria and Orchis latifolia are used as food.
• The roots of Vanda are used as curative for rheumatism.
• The dry pulpy fruit of Vanilla planifolia provides vanilla for commercial purposes. 
• Many orchards bear sweet-scented flowers so they are cultivated in greenhouses due to their high demand as compared to other flowers.

Conclusion 

Orchidaceae is also known as orchids. They are one of the two largest flowering plant families. They are a large and diverse group of flowering plants with brightly coloured and fragrant Blossoms. The plants are perineal using pseudobulbs or root tubers. Leaves are simple with parallel veins. The flowers are large, coloured and scented. Flowers are solitary, terminal, sensible or pedicellate and bisexual. 

Stamens are usually three in number and unite with the pistil to form a column opposite to the labellum and act as functional. The gynoecium is usually tricarpellary and syncarpous. Ovary is inferior and unilocular. Placentation is usually parietal. Entomophilous pollination. It is the second-largest family of angiosperms which are cosmopolitan in distribution. In India, there are about 130 genera and 800 species of Orchidaceae. The family is of very less economic importance but many orchards bear sweet-scented flowers so they are cultivated in greenhouses due to their high demand as compared to other flowers. The tuberous roots of some of the species are used as food.