Orchidaceae is one of the largest families in flowering plants consists of 899 genera and 28484 species.
Orchids show several forms of growth such as terrestrial, epiphytic and some are lithophytes. About 70% of orchids in the world are epiphytic. Majority of the temperate orchids are terrestrial while tropical orchids are epiphytic or lithophytic. Epiphytic orchids grow and attach themselves to host trees or small twigs on the top of the tree canopy. Epiphytes usually have a strong developed root system and expose them to the air or the crevice and bark of host tree to absorb the moisture and nutrients. Terrestrial orchids grow in humus or leaf litter on the forest floor and can adapt to various growing conditions like boggy ravines, damp forest floors, sandy dunes and even semi-arid desert soil. Terrestrial orchids form tubers into the soil and use their underground roots to get the soil nutrients. Terrestrial orchids have deciduous flowers and leaves as they will drop during the winter. Lithophyte orchids grow on the exposed rocks. Leaves of the lithophyte orchid usually looked fleshy. The roots will burrow into crevices to receive water and nutrients from the rainwater, surrounding moss and organic debris. Lithophyte orchids have pseudobulbs which can store water to help the plant live through dry spells.
Growth Cycle and Growth Pattern of Orchid
An alternating cycle of growth periods and rest periods controls the life of orchid. By exposing to too much moisture in the rest period, the orchids will not flower and only form weak shoots. Growth pattern of orchids can be divided into monopodial and sympodial. Monopodial orchids grow up off a single central stem with leaves on either side while sympodial orchids show multiple growths and usually grow one or more new growths per year. Each new growth comes from the side of the one and in a circular pattern.
Dendrobium (Subfamily?: ?Epidendroideae) is one of the most popular genera in Orchidaceae, with approximately 1,523 species in the world. Dendrobium belongs to the sympodial epiphytic orchid, was recognized by Olof Swartz in 1799. Dendrobiums are distributed in tropical regions where there are high annual rainfalls and without too much seasonal variation around the whole year. Dendrobiums are native to Southeast Asia and occur in diverse habitats except in the coldest and driest region.
The life cycle of the Dendrobium orchid includes flowering phase, growing phase and dormancy. They grow quickly from summer to fall and remain dormant during the winter. New shoots will be formed and start flowering in spring. Dendrobiums can be divided into evergreen and deciduous. Evergreen Dendrobiums bloom on the new growth, have cane-like stems and papery green leaves, bear the flowers in erect panicles and singly at the nodes. Deciduous Dendrobiums bloom on the old canes, dry and shrivel like bamboo canes after the leaves drop off.
Dendrobiums do not use host food supply since they have specialized root structure to absorb water and accommodate mycorrhizal fungi for nutrients. Some of the stems (pseudobulbs) are green and succulent while others are long, thin, swollen and fibrous. Dendrobium flowers are small to medium size with a narrow claw lip or without side lobes. Some Dendrobiums can self pollinated and others are pollinated by insect. Dendrobiums will produce capsule fruit and very small seeds with a spherical ovoid embryo inside each seed.
Dendrobium needs an abundance of light to grow well and about 75% of sunlight is required for the plant growth. Dendrobium can withstand direct sun early in the morning or evening but require shading between 11am to 3pm where the light intensity is too high. The optimum light will produce healthy and attractive blooms while light deficit causes dark green leaves formed. Yellowish or brownish leaves with spots on the underside represent sunburn. Dendrobium grows best at night temperatures between 15-18?C and day temperatures between 23-29?C. About 50-75% of humidity is required for Dendrobium and excessive humid condition will cause fungal and bacterial infection. The infection can be cut down by air circulation to cool down the plant. Aeration is important to maintain the orchid health and dry the excess moisture. Dendrobiums prefer rainwater and are watered once a week. The roots are very sensitive and easy to become rotten. Thus, Dendrobiums always re-watered after the soil becomes dry.
Commercial Value and Market Demand of Orchid
Orchid cultivation began in 500 BC and is used for ornamental and medical purposes. The flowers they produce are extremely exotic and attractive, curious shapes, diverse colours, longer self-life, making them one of the top ten ‘cut flowers’ in international flower market. Orchids are commonly used as cut flowers and potted plants. They have huge demands and high prices in global floriculture market due to several properties.
Cattleya Labiata is the most popular orchid species and is known as the “Queen of Orchids” for its colourful appearance and wonderful aroma. Cattleya is widely used in brooch accessories and floral decorations. Due to the small size of the flowers, Cymbidium orchid is also used as a brooch accessory. Their tall stems and long leaves and long-lasting aroma make them one of the first choice for orchid lovers. Dendrobium with wide variety of colours and shapes has high demand in international floriculture market. Miltonia orchids have large flowers that make them ideal for bouquets and perfumes as well as indoor flowers. Phalaenopsis is known as “Moth Orchid” because the flowers resemble a flying moth. For most beginners, these plants are the preferred orchids because they can tolerate under many conditions. Vandas is known as “Singapore Orchid” and is mainly from Southeast Asia. Their flowers bloom in different colours and their stems are long. Vandas can be placed in the hanging basket.
Orchids have been widely used in traditional Chinese medicine. Many orchids have been proven for their medicinal properties. Medicinal orchids mainly belong to genera: Calanthe, Coelogyne, Cymbidium, Cypipedium, Dendrobium, Epthemerantha, Eria, Galeola, Gastrodia, Gymnadenia, Habenaria, Ludisia, Luisia, Nevilia and Thunia. Orchids contain phytochemicals such as alkaloids, flavonoids, carotenoids, anthocyanins, sterols, bibenzyl derivatives and phenanthrenes. These phytochemicals are important secondary metabolites which can provide antimicrobial, antitumor, anti-inflammatory, antiviral and other functions. Nearly 145 bioactive molecules have been isolated from various orchid species, which are used for the treatment of different and ailments like tuberculosis, stomach disorders, jaundice, eczema, inflammations, menstrual disorder, diarrhea, muscular pain, rheumatism, malaria, wounds and sores.
Several species of orchids are used as potent inhibitor against gram positive and gram negative bacteria and are proved to be a potent antimicrobial agent. Gastrodianin, a protein isolated from orchid Gastrodia elata have shown invitro activity against plant pathogenic fungi. Vanillin, the major flavoring component of vanilla is a membrane active compound which results in dissipation of ion gradients and the inhibition of respiration. Vanillin has shown antimicrobial activity against Escherichia coli, Lactobacillus plantarum and Listeria innocua. Heptacosane (C27H56) and octacosanol (C28H58O) showed marked anti-inflammatory activity in carrageenan induced oedema in rats and mice is reported from Vanda roxburghii. The anti-inflammatory activity is due to long chain alkanes and alkanols (ranging C-27 to C-32) which are ubiquitous in plants. Dendrobium has great medicinal characteristics as about 40 species have been used in traditional Chinese medicine. Dendrobium nobile is a good source of compounds with antitumor activity. Denbinobin and 4,7-Dihydroxy-2-methoxy9,10-dihydrophenanthrene from Dendrobium nobile showed cytotoxicity against human lung carcinoma, human ovary adenocarcinoma and human promyelocytic leukemia cell lines. Dendroside A and dendronobiloside A obtained from the stem of Dendrobium nobile showed stimulatory effect on proliferation of murine T and B lymphocytes . Cirrhopetalanthrin which has shown cytotoxicity against human colon cancer (HCT-8), human hepatoma (Bel7402), human stomach cancer (BGC-823) human lung adenocarcinoma (A549), human breast cancer (MCF-7) and human ovarian cancer (A2780) cell lines is isolated from Cremastraappendiculata. Compounds with anti tumor activities have also been isolated from Bulbophyllum kwangtungense. Alkyl ferulates with antioxidant properties has been isolated from methanolic extract of Dendrobium monoliforme. Other antioxidants such as cis & trans-Melilotoside, dihydromelilotoside has been isolated from Dendrobium sp.. Acanthephippium bicolor Lindley was reported to be one of the best herbal medicine for Urinary Tract Infection and leaves can be used as herbal and scientific medicine throughout the year as there is no seasonal impact.