Orchid Biological Structure
Orchids have three unique characteristics that differentiate them from other flowers: their flowers, reproductive parts (column), and roots.
The Orchid Flower
Orchid flowers are bilaterally symmetrical, which means they can be divided vertically into two identical mirror-image halves. The appearance of the flowers can range from stunningly beautiful to peculiar, depending on factors such as size, texture, color, and shape. Despite their diversity, orchid flowers typically consist of three sepals and three petals arranged in a whorl, along with a reproductive column.
The orchid flower is composed of two whorls, the outer whorl being the sepals and the inner whorl being the petals. Sepals can often be mistaken for petals due to their similar size and color. However, in some orchid species, the dorsal sepal is larger and more prominent than the lateral sepals, which can sometimes appear fused.
The petals of the orchid are typically more showy than the sepals, but there are exceptions. In some orchid species like Masdevallia, the sepals are more spectacular than the petals, with one petal located at the bottom of the flower and modified into a lip or labellum. The orchid lip varies in shape, form, and color, and is often the largest and most ornate feature of the plant. Its purpose is to serve as a landing pad for potential pollinators, luring insects with its extravagant shape and coloring.
Different orchid species have evolved specialized lips to attract specific pollinators, such as flies, birds, gnats, moths, butterflies, and even hummingbirds. For example, in Bulbophylums, the lip is a sensitive hinge that swings to propel visiting pollinators towards the pollen, while in Paphiopedilum, or lady slipper orchids, the lip is in the shape of a slipper-like pouch that traps the pollinator until pollination is complete.
Most orchid species have resupinate flowers, where the lip starts at the top of the flower bud and moves downward as the flower matures. However, there are some exceptions, such as the Encyclia cochleata, which has a non-resupinate flower where the lip remains at the top of the flower and traps the pollinator underneath a hood.
The Orchid Column
The reproductive parts of orchids are quite unique, as the male and female organs are fused into a tubular, waxy structure at the center of the flower known as the column. In conventional flowers, the male (stamen with pollen) and female reproductive organs (pistil with stigma) are separate. At the top of the orchid column, the pollen grains form a golden yellow waxy mass called the pollinia, which are contained in the anther cap. The number of pollinia varies between orchid species and represents the male reproductive organs.
On the underside of the column, immediately behind the tip, is the sticky stigma, which is adapted for pollination purposes and represents the female reproductive organs.
The Orchid Roots
The roots of plants typically serve two basic purposes: anchoring the plant and absorbing moisture and nutrients. Orchid roots also serve these purposes, but with a distinct difference. The orchid root is generally thicker than that of a normal 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, called the velamen. This velamen is essentially air-pockets of dead cells that provide the roots with high absorbency. The outer layer of the roots is often covered with fine hair-like projections that resemble the roots of conventional plants.
Terrestrial orchids typically have underground roots that perform the usual conventional root functions. Aerial roots are typically found on epiphytic orchids, which grow on rocks and trees. Aerial roots are usually thick and strong with super absorbency capabilities. They attach the orchid to a host tree or rock, allowing the plant to literally live on air. The aerial roots often have green tips that contain chlorophyll (especially in leafless orchid species such as Chilochistra parishii), which is required to absorb energy from the sun.
The Orchid Leaves
Orchid leaves exhibit a wide range of variations, similar to their flowers. They can be broad, thin, cylindrical, succulent, tiny, or even as long as over a meter (three feet). The majority of orchid leaves are green, blue, or grey in color, but there is a group of orchids known as jewel orchids that have leaves in shades of grey, green, red, brown, silver, bronze, and even copper tones.
The growth pattern of orchid leaves can also vary, ranging from fan-shaped to having intervals of a few to several centimeters between them. These variations reflect the orchid’s ability to adapt to different environmental conditions.
For instance, some Vanda orchid species grow in shaded areas and have broad, flat, or pinnate leaves to maximize exposure to sunlight. Brassavola species, on the other hand, naturally grow in tropical regions with harsh sunlight, and their leaves are fleshy and pencil-shaped to minimize the surface area and conserve moisture.