Learn About Orchids and Orchid Care

Learn About Orchids and Orchid Care

Tuesday, March 15, 2005

Orchid Flowers

Orchids are truly flowers of superlatives. Even a complete layman in botany is awed by the beauty of orchids. No plant family has as many different flowers as the orchid family. 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 multicolored. Some orchids only grow one flower, others sometimes more than a hundred.

The typical orchid flower is zygomorphic, i.e. bilaterally symmetrical. 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. When the flower opens, the sepals become colored. 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 Paphiopedilum (Venus Slippers) 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.

The reproductive organs in the centre (stamens and pistil) have been transformed into a cylindrical structure called the column or gynandrium. On top of it lies the stigma and the remains of stamens, 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.

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