ORCHIDS FLOWER

There are many types of specializations within the Orchidaceae. Best known are the seemingly endless structural variations in the flowers that encourage pollination by particular species of insects, bats, or birds.
Most African orchids are white, while Asian orchids are often multicolored. Some orchids only grow one flower on each stem, others sometimes more than a hundred together on a single spike.
The typical orchid flower is zygomorphic, i.e. bilaterally symmetric. Notable exceptions are the genera Mormodes, Ludisia and Macodes.
The flowers grow on racemes or panicles. These can be :
• basal (i.e. produced from the base of the pseudobulb, as in Cymbidium)
• apical (i.e. produced from the apex of the orchid, as in Cattleya)
• or axillary (i.e. coming from a node between the leaf axil and the plant axis, as in Vanda).
The basic orchid flower is composed of three sepals in the outer whorl, and three petals in the inner whorl. The medial petal is usually modified and enlarged (then called the labellum or lip), forming a platform for pollinators near the center of the corolla. Together, except the lip, they are called tepals.
Sepals form the exterior of the bud. They are green in this stage, but sometimes, if the orchid blossom is, for example, purple, the buds can show a purple tint. When the flower opens, the sepals become intensely colored. Sepals may mimic petals such as in some phalaenopsis or be completely distinct. In many orchids, the sepals are mutually different and generally resemble the petals. It is not always easy to distinguish sepals and petals. The normal form can be found in Cattleya, with three sepals forming a triangle. But in Venus Slippers (Paphiopedilum) the lower two sepals are concrescent (fused together into a synsepal), while the lip has taken the form of a slipper. In Masdevallia all the sepals are fused into a calyx. In an example like this the sepals are very prominent, especially in lycaste orchids, the actual petals become diminished and inconspicuous.
The reproductive organs in the center (stamens and pistil) have adapted to become a cylindrical structure called the column or gynandrium. On top of the column lies the stigma, the vestiges of stamens and the pollinia, a mass of waxy pollen on filaments. These filaments can be a caudicle (as in Habenaria) or a stipe (as in Vanda). These filaments hold the pollinia to the viscidium (sticky pad). The pollen are held together by the alkaloid viscine. This viscidium adheres to the body of a visiting insect. The type of pollinia is useful in determining the genus. On top of the pollinia is the anther cap, preventing self-pollination. At the upper edge of the stigma of single-anthered orchids, in front of the anther cap, is the rostellum, a slender beaklike extension.