Friday, November 23, 2012

Orchid Plants

       The Orchidaceae are a diverse and widespread family of flowering plants with colorful and fragrant blooms, commonly known as the orchid family. Along with the Asteraceae, they are one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species, found in 880 genera. Selecting which of the two families is larger is still under debate, as concrete numbers on such enormous families is constantly in flux. Regardless, the number of orchid species equals more than twice the number of bird species, and about four times the number of mammal species. The family also encompasses about 6–11% of all seed plants. The largest genera are Bulbophyllum(2,000 species), Epidendrum(1,500 species), Dendrobium (1,400 Species) and Pleurothallis (1,000 species).



              Orchid bloom times can be quite variable depending on the growing environment and the hybridization of the plant. For example, the hybrid Doritaenopsis, a cross between Doritis and Phalaenopsis, blends the summer bloom time of the Doritis parent with the larger blooms of the Phalaenopsis parent creating nice hybrids that look much like a Phal but bloom longer into the summer. Also, some orchids can be forced into bloom by altering the temperatures. For example, phalaenopsis growers may chill the growing area to trick the plants into thinking it is Fall and setting a bloom spike accordingly. As a result, a plant that is in bloom when purchased is likely to adapt to its environment and set its own bloom cycle based upon its new home. As an example, a plant that is in bloom when purchased in the fall may bloom every winter after that in its new environment.
            The structure of orchid flowers is unique among floral plants. The orchid flower is typically has an outer whorl of three sepals, an inner whorl of three petals, and a single large column (the gynostemium, composed of the male stamens attached to the female pistil) in the center.
            The sepals are the protective cover of the flower bud. When the flower opens, the sepals may become enlarged and colored. In most species, the sepals are equal sized and look like petals. In some species, however, the top, or "dorsal" sepal becomes very large and showy, the two lower "lateral" sepals are sometimes fused into one structure, and in other species all three sepals are fused forming a bell-shaped structure around the flower. In some species, the display of the sepals completely overwhelm the actual flower.
            The two lateral petals flank the greatly enlarged flamboyant bottom petal (lip or labellum) which is usually highly modified to attract and, in some cases, trap potential pollinators. The lip may be differently colored or marked, ruffled or pouch shaped, decorated with crests, tails, horns, fans, warts, hairs, teeth, or other decorations attractive to their selected pollinator.
            The orchid's reproductive organs are combined into a single column (a gynostemium) unlike the usually separate male stamen/anther and female pistil/stigma configurations of other flowers. This is the primary identification feature of an orchid. At the top of the column is the male anther which contains packets of pollen called pollinia. Below the anther is the stigma, a shallow, usually sticky cavity in which the pollen is placed for fertilization. There is a small growth, called the rostellum which acts as a protective barrier to prevent self pollenation. Some species produce separate male and female flowers to prevent self pollenation.
           The overall flower shape is characteristically bilaterally symmetrical (the left and right halves of the blossom are mirror images), a necessity for reliable pollenation by bees.
            In the bud stage, the lip is the uppermost petal. In most (but not all) orchids, as the flower opens, the flower twists 180° around its flower stalk to position the lip on the bottom. This unique process is called resupination. Some orchid flowers remain "upside down" or non- resupinate while other flowers will rotate in a complete 360° circle ending back in the original upside position!
Most orchid growers are aware of the two methods of propagation:  1) Sexual Reproduction.  2) Asexual Reproduction. 
I. Sexual Reproduction 
    In sexual reproduction, seeds are placed on special culture medium to germinate.  Young plants are transplanted to individual pots to continue to grow.  Using the sexual reproduction method, I can see at least two drawbacks:  1)  The purity of rare species may not be kept for long as hybrid may occur and the original plant thus faces extinction.  2)  The rarity and value of your one-and-only species may lessen once it is allowed to be reproduced on a massive scale.         It is much better to preserve a rare species so that more people can enjoy it than to let extinction be its fate. 
II. Asexual Reproduction
    The most up-to-date method is that of Tissue Culture.  First, tissue is taken from the growing point of the parent plant.  This tissue is cut into tiny pieces and put them on the culture medium and kept on shaking while being in the container.  In time, these tiny pieces of tissue will form roots and shoots and become tiny plants.  These tiny plants continue to grow and finally become adult plants after transplanted to individual pots. However, no matter whether we use seeds or tissue culture for reproduction, we need to have a high level of technology, appropriate equipment as well as an aseptic environment.  Needless to say, such requirement is not within the reach of the average orchid grower's budget or capability.  Hence his only hope is perhaps to wait for the rare opportunity of having a shoot appear from a stem or from between a leaf and the roots.  Some orchid growers apply hormones to stimulate the plant to produce new shoots.