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.
