There are three distinguishable characteristics of orchids that set them apart from other flowers in the floral kingdom. These are the flowers, the reproductive parts (or column) and the roots.
The Orchid Flower
The orchid flower is bilaterally symmetrical. This means that every orchid flower can be divided on a vertical plane, and a vertical plane only, to produce two identical halves that are mirror images of each other. When taking into account factors such as size, texture, color and shape the flowers itself range from awesomely beautiful to quite bizarre. However, there is also a common thread – the orchid flower consists of three sepals and three petals that are arranged in a whorl and a reproductive column.
The sepals and petals form the outer and inner whorls of the orchid flower. Often the sepals can be mistaken for petals due to its color and texture and they are usually of equal size. In some orchid species the dorsal or upper sepal can be slightly larger and more prominent than the lateral or lower sepals. These lower sepals can sometimes also appear fused. The petals are more 'flamboyant' than the sepals. But this is not always the case because there are orchid species like the Masdevallia where the role of flamboyancy is reversed and the sepals are more spectacular than the petals. In the Masdevallia the one petal is located at the bottom of the flower and modified into a lip or labellum.
The orchid lip can vary in shape, form, and color. It can be resemble a trumpet; it can be fringed, curved, elongated or even pouch-like. Sometimes it can even be stripes, or speckled, or very bright or subdued in color. Often you will find that the lip of the orchid flower is the largest, most ornate feature on the plant. Some orchid species exhibit the total opposite.
The purpose of the lip is to act as a landing pad for insects that may be potential pollinators. The lip will lure the bee (or other insect) with its extravagant shape and coloring. Often in these cases the lip look like a single, or multi-lobed structure that is decorated with ridges, bumps or tufts of hair.
There are several orchid species that are fussy regarding the pollinating agent that they require for reproduction purposes. In the event of the orchid depending on flies, birds, gnats, moths, butterflies, or even humming birds, the lip is especially 'engineered' by the orchid to facilitate the pollinating agent and the pollination that is required from it. In Bulbophylums for instance the lip is a sensitive hinge that swings to propel the visiting pollination agent towards the pollen. In the Paphiopedilum orchid, or the lady slipper orchid, the lip is in the shape of a slipper-like pouch that will trap the pollinating agent until pollination is complete.
In the majority of the orchid species known at present day, the lip is located at the bottom of the orchid flower. When the flower is still in bud, the lip is located at the top and as the flower matures, the lip moves downward. This process is called resupination. Few orchid species are non-resupinate, like the Encyclia cochleata where the lip remains at the top of the flower and performs is pollinating duties in a different fashion. (It traps its pollinating agent underneath the hood.)
The Orchid Column
The orchid column or reproductive parts are quite unique. This is mainly due to the male and female organs being fused into a tubular, waxy structure at the center of the flower known as the column. With the conventional type of flower has separate male (the stamen with the pollen) and female reproductive organs (the pistil with the stigma). At the top of the column, the pollen grains form a golden yellow waxy mass called the pollinia. These pollinia are contained in the anther cap. The number of pollinia varies from orchid species to orchid species and represents the male reproductive organs.
Immediately at the back of the tip, on the underside of the column is the stigma which is quite sticky and thus adapted for pollination purposes. The stigma represents the female reproductive organs.
The Orchid Roots
First and foremost, the roots of plants usually serve two basic purposes: anchoring the plant and absorbing moisture and nutrients. Orchid roots also perform the same purposes, but with a distinct difference. The orchid root is generally thicker than those of a normal conventional plant and may even appear as individual strands. The roots have a fragile inner core that is protected by a thick spongy layer or grey, white protective tissue, the velamen. This velamen is essentially air-pockets of dead cells that provide the roots with that high absorbency. The outer layer of the roots is often covered with fine hair-like projections that resemble the roots of conventional plants.
The underground roots of terrestrial orchids usually perform the usual conventional root functions for the orchid. Aerial roots are usually on the epiphytic orchids. These plants usually grow on rocks and trees. Aerial roots are normally thick and strong with super absorption capabilities. The roots attach the orchid to either a host tree or rock and then the plant literally live on air. The aerial roots usually have green tips that contain chlorophyll (especially the leafless orchid species such as the Chilochistra parishii) that is required to absorb energy from the sun.
The Orchid Leaves
Orchid leaves are just as varied as the flowers. It can be broad, thin, succulent, cylindrical, tiny and even as huge as more than a meter, i.e. three feet in length. Most of the orchid leaves occur in shades of green, blue and grey. There is however, a group of orchids that have leaves that are shades of grey, green, red, brown, silver, bronze and even in copper tones – the so-called jewel orchids. Orchid leaves can grow in various ways: fan shape, at intervals ranging from a few to several centimeters in between. Whichever way it grows, it reflects the adaptations of the orchid to its environmental conditions. For example some Vanda orchid species grow in shaded areas and thus their leaves are broad, flat or pinnate for maximum exposure to sunlight. The other example that warrants mention here is the Brassavola species which grow naturally in tropical regions in harsh sunlight. Their leaves are fleshy and pencil shaped to as to expose the minimal surface area of the plant and retain moisture.