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|Vol. 6(2), pp. 4-10||The McAllen International Orchid Society Journal||February 2005|
Until the explosion in orchid plant mass marketing in recent years, most ordinary individuals in the United States were introduced to orchids via a flower of a Cattleya or a Cymbidium. In fact, for many a Cattleya flower was the only "real" orchid. It was the flower of a wedding bouquet, or the flower if Susie was "really special" and her date was financially much better off than the average high school prom escort. Now, as the 21st Century is well underway, an individual's introduction to orchid growing is likely to be via a Dendrobium, Oncidium, or Phalaenopsis plant mass-grown in Taiwan, Thailand, or Hawaii, then middle-manned to a wholesaler, then to the garden department of Lowe's, Home Depot, or a mom-and-pop "ship in and sell out" greenhouse business. The tag on the hybrid orchid plant may say "Dendrobium orchid," Oncidium Orchid, or Phalaenopsis Orchid, which gives the buyer no knowledge about what hybrid it is, and even less about how to grow it so it flowers the next time around. However, that enters an entirely different can of worms! For now, let's take a few of the more common orchid genera one by one, note similarities and differences between them, and throw in some of the cultural advice that applies to both species and their hybrids.
We'll begin with Cattleya. Old line readers of the MIOS Journal will be able to go back to Vol. 2(9): 6-8 and read about this genus in detail. New members of the MIOS have two other choices: (a) do without; or (b) obtain the back year [each year is a paltry $20 for the 12 issues except for Vol. 1 (2000) which began in August. It's $15.]. Some of that reference's information may be repeated here, in passing, but most of it will not. O.K., so much for that reference. The genera Cattleya and Laelia are quite similar. In fact, Cattleya derives from having four pollen masses while members of Laelia have only two, but we're getting in deep water already. Suffice it to say and that most of our general remarks about "Cattleya-type" plants will apply to members of Cattleya, Laelia, Encyclia, and a few other similar genera (e.g. Brassavola, Rhyncholaelia, and others.) These are New World genera. They're native to Mexico and southward into South America, and have been much used in making hybrids!
These plants have a rhizome. That's the long almost thick-tubular group of cells that lays along whatever the substrate is. At various points (segments) along the rhizome the pseudobulbs grow upward while the roots reach outward and usually somewhat downward to grip and hold the plant onto its substrate (tree branch, wall, tree fern plaque, or pot). The new shoot is the new growth. It grows out from an "eye" on the pseudobulb, then grows upward and forms leaves, and at its base new roots begin to erupt. As the shoot matures, its "stem" swells to form the nutrition storage device we call the pseudobulb. With this short summary, we'll proceed to the plant's various parts.
Fig. 1. A portion of a typical Cattleya-type plant. (roots, rhizome, pseudobulb bases, and shoot)
Rhizome: We begin at the base of the plant (Fig. 1). Note that the roots erupt from the rhizome only where the pseudobulbs grow from it. The spaces in between pseudobulbs are called segments, and their lengths can vary from quite a bit to next-to-nothing! Point: when you repot this type of plant, the rhizome should be just barely visible, on top of the potting mix! If it's covered a tiny bit, or just sprinkled with Sphagnum moss dust, that's O.K., but if you really want a fine way to kill an entire plant division, one way to do it is to bury the rhizome three or four inches (or more) deep in the potting mix! Don't do it! Cattleya-type orchids are not lilies or Amaryllis plants! The rhizome, pseudobulb bases, and any new shoots will get no light, but what they will get is excessively wet,...and stay that way,...and rot! If a new shoot does make it up out of this covering, it'll grow for a bit and then rot at the base. In fact an entire mature plant can be very nicely killed this way! In nature, or in the case of an orchid-in-culture that should have been repotted two or three years ago, the rhizome may grow to the point of becoming entangled among other growths and even end up well below the surface of the substrate. When this happens, the plant may look like a grandiose "specimen" plant, but you can pretty well be certain it's not been given enough spread-out room so it could really grow and show at its best. When rhizomes start overlapping and growths are getting entangled, it's time to dis-entangle a few things and give the plant growths the room to do their best. This doesn't happen in nature, but plant growing in nature is a dog-eat-dog survival thing that doesn't produce optimum flowering, while most orchid culture by humans is oriented to producing pretty flowers.
Point: grow the plant as you like, but realize that the large "specimen plant," while spectacular, may not be giving you its best-possible flower production.
Roots: As touched on above, the roots have two primary functions: (a) they convey water and minerals upward to the other plant parts; and (b) they act as "hold-fasts" to anchor the plant at a particular site. That's not all they do, but that's a lot of it. Roots are a plant part all-too-often neglected when orchid culture is undertaken. Consider: when a plant's repotted, no matter how careful the operation is, roots are going to suffer some damage! Therefore, a prime concentration after repotting should be to grow roots! Don't keep the new plant soaking wet for weeks after repotting! Keep it somewhat on the dry side, and as new roots begin to proliferate, the watering can be increased. Remember; more orchids get killed by over watering than any other cultural practice, and this is even more critical for orchids that have been newly repotted or remounted! With the rhizome laying just at the potting mix's surface, you'll be in a better position to see new roots growing. Don't touch and damage them, and particularly don't touch the green root tips! You don't have eyes in your fingers! Look with your eyes, and let the roots remain untouched!
The new growth, or shoot(s): The shoot is that little nub-like growth protruding from the right side of the rhizome in Fig. 1. We'll say more about the shoot as we discuss pseudobulbs, but for now let's consider the shoot itself as it's grown more than just a couple of centimeters. Picture a line of flexible ice cream cones stacked together. The outermost cone is covered with the greenest and hardest tissue, and successively the inner tissue-cell-layers become whiter and more delicate until we reach within the innermost "cone." These innermost cells are all the same. They'll become whatever they're eventually to become depending on the position into which they grow, but for now, these are undifferentiated primordial cells that eventually could become a plant in their own right! Let's suppose we dissect out this small group of cells under sterile conditions, discarding all the others of the shoot. Now we chop this little group into tiny cell clumps and position them atop an agar-jelly medium in a sterile flask, and give them light-and-dark periods simulating day and night. These cells grow into genetic copies of the original plant, and we say we have "cloned" the plant. One dictionary definition of a clone is:
a group of genetically identical individuals resulting from asexual, vegetative multiplication, i.e. by mitosis: any plant propagated vegetatively and therefore considered a genetic duplicate of its parent.
Well and good, but how do we tell the parent from the clone when all the plants are mature? They're all the same genetic material! The fact is that we can't tell any difference, and it's here this definition of a clone breaks down. Actually, the parent is a "clone " itself in that it's a unique conglomeration of cells having a particular unique genetic code. In short, there's nobody like you but you! So what's the problem with cloning a human? It's been done with sheep, mice, and even a pet cat, and a lot of it began over thirty years ago with,...you guessed it, orchids! It's been called mericloning, meristemming, cloning, and a few other names along the way, but one thing is certain; cloning is not something that's newly burst onto the scene!
While we're on the subject, what's the big flap over somebody cloning a human? Well other than various religions inserting their disapprovals about individual humans controlling their personal reproductive abilities, there's the Hollywood propaganda about some weird-oh making a thousand Einsteins or a thousand Hitlers (or some such thing) and kicking off a "war of the clones." However, let's be realistic! Suppose your editor had the ability to clone himself and did so (please, restrain laughter and nasty comments at this point: it's only an example). O.K., your editor clones himself and, in fact, makes five copies of this wonderful person. Consider what happens next. One baby goes to a Chinese couple, another to a couple in Saudi Arabia, another to a couple in Israel, another to a couple in Mexico, and the last one gets reared by an "average couple" in the U.S. All the kids grow to age 25 and then meet. All look alike and even have the same fingerprints, footprints, and DNA, but there the ballgame ends! When they meet, it's like having five different environments suddenly thrown into the same dinner party! Are they the same? Only genetically! When it comes to humans, environment plays a monumental part! We could create a lengthy novel with this scenario, and at the present it would be a work of fiction, but one wonders whether some variation of this now-fictional novel might not, at least in part, surface-in-fact in the not greatly-distant future... ! The reality is, however, that environmental factors and the passage of time and events mitigate against making a thousand identical robot-like clones to serve as some Dr. Strangelove's army. Now that we've dabbled with the downside of cloning, there's an upside to it. Given a highly desirable plant, we can meristem it and produce many genetically identical copies, and it can become cheaply available for many to enjoy, rather than just a few! Yes, much of the foundation research in cloning has had its roots in people who've worked with orchids, and it wasn't to make world-dominating armies, but to make many more plants that bear especially beautiful flowers! Perhaps there's some hope for humanity after all. Isn't is interesting what avenues one might pursue as one seeks to understand the complexities of a new shoot on an orchid plant?
Summary: the rhizome is the link that holds the plant parts together, and it's the portion that continues to form the new "leads" or "shoots" for the plant's growth. Look at it! It's green! It does photosynthesis just as do the pseudobulbs and leaves. In nature, many of the Cattleya-types grow on trees, so the rhizome stayed exposed, so pot or mount a Cattleya-type plant division so the roots get anchored down in the mix, but leave the rhizome laying slightly embedded or atop the potting mix,...and give the new shoots the time and space in which to grow!
Fig. 2. A typical group of pseudobulbs. The oldest, left, are backbulbs and lack leaves. The more recent ones, at right, bear leaves.
Pseudobulbs (Fig. 2) are thickened stems, usually aerial. We like to think of the new shoot usually growing upward, but actually it reaches toward whatever direction the best light is coming from! As it does, the shoot looks like a cone; sort of like a newly sprouted corn plant. Outer layers of the "cone" may even form a thin paper-like sheathing around the newly forming pseudobulbous stem (check the one on the far right in Fig. 2). Actually, Cattleya-types occur as more than one-leafed plants. There's a whole group of Brazilian bifoliate cattleyas, and some of the types from the Myrmecophyla and Schomburgkia cousins have even more. However, let's stick with our one-leafed example. The shoot grows upward, finally becomes a "stem-with-a-leaf," and then the "stem" portion begins to swell as it continues its growth to maturity. Cattleya type orchids tend to grow in a wet-dry seasonal environment rather than the severe hot-cold seasons we experience in the Northern Hemisphere, so toward the close of the wet season, the pseudobulbs are mature food-storage devices. Now as the dry season takes hold, the sugars within the pseudobulb become more concentrated, the ambient temperatures vary, and the flowering cycle is initiated. From the apex (top end) of the pseudobulb, within where the leaf forms a little channel, a pair of thin, flattened, leaf-like structures (only joined at their margins) grow and form a semi-translucent sheath. Within this sheath, the tiny inflorescence begins to grow, but for now, we're only looking at pseudobulbs. In an old well-grown plant, you'll notice that as the new growths grow and mature, the old pseudobulbs gradually lose their leaves. Don't complain! They're still doing photosynthesis (making food for the plant!), but they're also translocating (through the rhizome!) nutrition forward to aid in making more sturdy growths ahead. In Fig. 2, you'll notice the three pseudobulbs on the left have lost their leaves. In the case of this plant, after it's done flowering this time, it could probably be divided to make a three-backbulb division and a three-leafed division. This is one way to have more plant-divisions in a short time. However, if space permits, and the plant is allowed to continue to grow without being divided, and, if its well-fertilized and given good cultural conditions, it may begin putting out not one new shoot at a time, but two,...and new shoots may even show up from a leafed growth a couple of growths back from the most recent one.
Summary: pseudobulbs are thickened stems and the plant needs good care so they're sufficiently sturdy to (a) support the leaf-and-flower growths, and (b) store and supply nutrition to support the flowering parts, and (c) eventually store enough nutrition to continue to translocate food forward as the plant continues to grow. Not fertilizing, or doing so with an overly weak solution, or having a sloppy fertilizing schedule, (or otherwise poor cultural practices!) can make for weak "lay-down" type pseudobulbous growths. Give the plant the fertilizer balance and other optimum cultural conditions it needs!
Fig. 3. Leaves of Cattleya-type orchid. (note sheath projecting vertically from the right leaf)
Now to leaves (Fig. 3)! The leaf is the plant's factory for converting carbon dioxide, light, minerals, and water and uniting all these factors into the sugars the plant needs for growth. The carbon dioxide comes from the air. Add sunlight, water and minerals (all in optimum amounts, of course), and the plant flourishes within an envelope of variable temperatures and humidities best for that species. To do their photosynthesis thing, orchid leaves are aided by the pseudobulbs, the rhizome, and even--to some extents--the roots. The roots too? Yep! Take a healthy plant that has abundant exposed root growth and sprinkle it thoroughly with water. Notice how the otherwise white roots suddenly get green? This are chlorophyllous cells showing through the thin layer of otherwise white (but transparent) tissue called velamin.
Orchid leaves are the high-productivity factories to produce the nutrition necessary for flowering, fruiting, and seed formation. When all that's in the past, the leaf still produces food for the production of plant parts. However, all life forms go through the same cycles of beginning, growth, maturity, decline, and finally death, and leaves (like the cells that make up your hair, fingernails, and so forth) are no exception. When their productivity-usefulness has passed a certain point, they die and the plant sheds the leaf. This breaking-off cell layer is known as the abscission layer, and when the old leaf drops, the exposed cells at the plant's abscission layer seal off that plant part to deter incoming pests and avoid moisture loss to the outside world.
Fig. 4. The Cattleya-type flower.
Although they vary in particular orchid species, orchid flowers have three sepals which enclose three petals, with one of the petals differentiated to form a lip (formally called a labellum). Seen face-on (Fig. 4), the sepals are three simple structures; one points upward, the other two are similar and point downward angularly. Two of the petals are the lateral showy wings spreading at the sides, and the third petal is the tubular lip or labellum. In this figure, within the throat of the labellum just the tip of the column can be seen. The column's actually visualized better with a side view of the orchid flower, but that structure will be discussed when its variations can be compared with the columns of other orchid genera. For now, it will suffice to say that in the great majority of orchid flowers, this central column holds both sexes. Most orchid flowers are perfect, that is to say they contain both sexual parts. The male portion is fairly simple. It's at the end of the column, and is composed of the throw-away anther cap enclosing the pollinia (the male sperm cells). The female receptacle cavity is a bit farther back. The pollen unit is actually in three parts. When deposited in the sticky female receptacle cavity, one part forms a tube that actually grows down the length of the column, past where the petals and sepals join the column, to the ovary. The other two pollinia travel down this tube, into the ovary, and fertilize the many embryos located there, and in orchids, when we say "many embryos," we really mean it! The number of seeds produced by a single seed capsule of a Cattleya-type orchid flower number right around a million or more! They're tiny! Actually, orchid seed looks a lot like just so much talcum powder. An orchid seed is composed of the genetic material and a seed coat,...that's it! There'll be more about seeds in the future, but for now, we'll leave it at that.
The orchid flower's structure is essentially what makes an orchid an orchid, and the flowers are the reason most people have any interest in orchids. Most, but not all. Plants of Vanilla planifolia are cultured for the vanillin in their seed capsules and seeds, and there's the human segment who propagates anything with anything and slaps the name "orchid" on it just for peddling purposes, but most people culture orchids because of their beautiful (and unusual) flowers. Still, another reason for the human interest in orchids is the very biological diversity of the family itself, but that's also grist for an entirely new batch of prose.
So why did we start talking about a flower and digress into words about an orchid seed? Well, the whole reason the plant wants to make a flower is to produce seeds. You see, the plant doesn't flower for our enjoyment; it does so to try to make more orchid plants! Humans go through all the work culturing orchid plants so they can enjoy the show when the flowers come. We're not usually interested in seeing anything happen much beyond that, so when the unfertilized flowers begin to wilt, they're discarded and we're back to the plant-growing cycle again. As serious orchid growers, we'll discuss orchid plant propagation via seeds at some future point, but for now, it'll suffice to consider at the basic structures of a few of the more common orchid genera.
Fig. 5. The Cattleya-type orchid plant.
We've discussed the basic vegetative and floral parts, with the various plant ad flowering parts figured as plant portions. Together, these are the basic parts of Cattleya-type orchids (Fig. 5). In the future, other orchid types will be compared and contrasted with each other and Cattleya-type orchids. It is planned to eventually include similar basic information for Cymbidium, Cypripedium, Dendrobium, Oncidium, Phalaenopsis, Vanda, and the orchid groups allied with these genera. However, the field is open for suggestions from local and corresponding members regarding similar discussions of other genera.