Orchid Parts and Why They Matter

June 2024 - by Sue Bottom / Illustrations by Terry Bottom

IT DOES NOT really matter if you can remember all the names of orchid plant parts, but it is to your benefit to understand how these parts function. We will talk about all the basic orchid parts to help focus your attention on things to look for when you are looking at your plants. Orchid growth habits fall into two basic groups: the monopodial orchids that grow vertically and the sympodial orchids that grow laterally.

Monopodial orchids, such as phalaenopsis and vandas, grow upward from season to season from a single vegetative shoot, or stem. Leaves, roots and flower spikes sprout from nodes along the stem. Normally the plant will lose its leaves from the bottom up and continue to grow new leaves from the terminal or apical tip while making new roots along the stem. Monopodial orchids do not have fleshy pseudobulbs for storage of food and water like the sympodial orchids, so they require more frequent watering and feeding. Vandas often produce a keiki (KAY- kee) a Hawaiian term for baby that is used to describe a plantlet that sprouts from a mature plant. Keikis are a great way to share your plants with friends.

Sympodial orchids, such as cattleyas, dendrobiums and oncidiums, branch outward horizontally rather than grow vertically like monopodial orchids. Sympodial orchids grow laterally and produce a new shoot along a rhizome that develops into a stem with roots and leaves and eventually produces flowers. This growth process is repeated in a continuous cycle. Sympodial orchids have pseudobulbs that grow along a rhizome (RYE-zohm), a root-bearing stem; the apex of the rhizome progressively sends up leafy shoots. When repotting, the rhizome should be at or just above the potting medium. There is a greater potential for rot if the rhizome is buried in the potting mix. A pseudobulb (SOO-doh-bulb) is the thickened portion of a stem used when discussing cattleyas, oncidiums and many other sympodial orchids. A cane, used when discussing dendrobiums, is similar to a pseudobulb but is much more stalk- like in appearance. The pseudobulbs and canes are like the humps on camels, storing food and water to sustain the plant during drought conditions. They perform a vital function to the plant even when leafless.

[1] monopodial orchids like vandas and phalaenopsis grow upward from a central stem.

[2] Sympodial orchids like cattleyas and dendrobiums grow along a rhizome, from which new pseudobulbs or canes emerge.

[3] the cataphyll protects the new growth when it is young, but sometimes must be peeled down to prevent water from collecting in the pocket and causing rot.

4] Unifoliate cattleyas have a single leaf.

Front bulbs are the pseudobulbs on the younger part of the plant. The front bulbs are the actively growing part of your plant and it is from these new growths that new flowers will emerge. The backbulbs are the pseudobulbs on the older part of the plant. The backbulbs are often without leaves but as long as they are still green, they continue to provide nourishment to the plant. Backbulbs can be used to propagate new plants from the original plant when new growths are encouraged to sprout from blind, or dormant, eyes, which are the incipient buds of vegetative growth. There are at least two eyes on each pseudobulb so that if one eye or lead becomes damaged, a new pseudobulb can emerge from the other eye. The cataphyll (KAT-a-fill) is an undeveloped leaf that forms around the base of the pseudobulb and matures to form a papery sheath along the length of the pseudobulb. When the pseudobulb is growing, the cataphyll provides some structural support and protects the tender new growth from mechanical and insect damage. Cataphylls can sometimes form pockets where water can accumulate and bacterial action can cause the bulb to rot so the pockets should be slit or the cataphyll pulled down so water will drain freely. Once the growth is mature and hardened, the dried cataphylls can be removed before they become hiding places for scale and other sucking insects.

Orchid leaves vary from the thin-leaved oncidiums and catasetums, the fleshy phalaenopsis to the hard dendrobium and cattleya leaves that have waxy coverings that help minimize water loss. Cattleyas with a single leaf are called unifoliates and cattleyas with two (and occasionally three) leaves are called bifoliates. unlike the unifoliates, bifoliate cattleyas should be repotted only when they are growing new roots. Stomata (sto-MAH-tah) are pores on the lower surface of the leaf epidermis through which the plant breathes. The stomata are mostly closed during the day to prevent water loss by transpiration and open at night when temperatures are lower and humidity is higher. This means that orchids are not good candidates for foliar feeding. If specialty foliar sprays such as those containing minor or trace elements designed to be absorbed through the leaves are to be used, they are best applied to the undersides of the leaves in the predawn hours.

[5] Bifoliate cattleyas normally have two leaves but strong plants may, depending on the species, produce three occasionally.

[6] You cannot have a healthy plant without healthy roots. Green root tips mean your orchid is growing and seeking out moisture and nutrients.

Orchid roots consist of an inside wiry filament and thick, sponge-like covering called velamen that helps prevent water loss and aids in absorption of water and mineral nutrients. Actively growing orchid roots have green (and sometimes reddish) tips; the longer the green tips, the faster the roots are growing. The white velamen layer follows a few days behind the root’s growth tip. The emergence of fresh roots tells you your plant is going into the growth mode. If it needs to be repotted, the time is now, or maybe you should have done it last week when the new growth was swelling up before the green tips emerged.

— Sue Bottom started growing orchids in Houston in the mid–1990s after her husband Terry built her first greenhouse. They settled into St. Augustine, Florida, Sue with her orchids and Terry with his camera and are active in the St. Augustine Orchid Society, maintaining the Society’s website and publishing its monthly newsletter. Sue is also a member of the AOS Editorial Board (email: sbottom15@gmail.com).

June 2024
The June 2024 issue contains articles from “ORCHIDS OF BHUTAN” to “CONRAD GESNER" and more.

Also in this issue

  • Tom's Monthly Checklist by Thomas Mirenda
  • Collector's Item - Cycnoches by Charles Wilson
  • For the Novice - Repot Your Plants by Ray Barkalow
  • Orchids Illustrated - Prescottia by Wesley Higgins and Peggy Alrich
  • Orchids of Bhutan - The Genus Thunia by Stig Dalström, Choki Gyeltshen, Nima Gyeltshen and Kezang Tobay
  • A Year of Observing Wild Cypripedium parviflorum var. makasin in Georgina Township, Ontario Canada by Edward McSweeny
  • Dendrobium bigibbum, Classifying for Exhibition and Approach to Judging by Peter Adams
  • Habenaria by Nicholas Rust
  • Parting Shot - Hierarchical Nomenclature by W.E.Higgins

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