Parts of an Orchid

Flowers

• An orchid's flowers grow singly or in an inflorescence, a group of flowers on an unbranched or branched stalk. Orchid flowers are called zygomorphs because they are symmetrical on just one axis. One of the orchid's defining parts are its petals. All orchids have just three petals and three sepals, which are outer segments of the petals. A lower, smaller petal is typically the most eye-catching and referred to as the labellum (lip). The orchid actually rotates 180 degrees to place the lip at the bottom of the blossom, making it easier for a pollinator to land on the flower. Depending on the orchid, the labellum or sepal may be fused together or reduced in some way, which is notable in orchids like the Masdevallia, which has small petals and lip and jointed sepals. The flower takes on a tubular shape in this case.

Reproductive Organs

• A true orchid is identified by its reproductive parts. The column sits above the lip and holds the flower's reproductive organs. The female stigma and male anthers sit fused at the top of the stamen. In other plants, the stigma and anthers are separate. The anther holds pollen in two sacs called thecae. This thick mass of pollen (pollinia) is attached to caudicles (stalks) and viscidia (discs). When an insect lands on the orchid, the pollinia sticks to it and is transferred to the stigma of another orchid the insect visits.

Stems

• Orchids may have one or many stems, depending on the variety. Monopodial orchids grow directly up, along one central stem. Sympodial stems grow across the soil or medium and have more than one stem. Varieties like Vanda are monopodial, and Cattleyas are sympodial. A stem may have nodes, which are joints on the stem or psuedobulbs that produce leaves or new growth. An orchid's root-bearing stems from which leafy shoots sprout are called rhizomes.

Roots

• Orchids have several distinctions in their root systems. Terrestrial (ground) orchids grow in soil, usually on a forest floor, grassland or woodland. Many of them loose their leaves and go dormant during winter months. Orchids are often a challenge to grow from seed because they depend on nutrients from mycorrhizal fungi living on their roots while being established. The orchid no longer needs the fungi once established. Orchid roots may grow from a stolon, or horizontally-growing branch. Roots on epiphytes, or air orchids that grow in trees, get nutrients from organic matter, water and dust accumulating around them.