Beginners Guide To Orchids Biology Essay
Orchid is one of the most fascinating, beautiful and peculiar variety among the flowering plants. They have always been considered difficult to grow. But given the right climatic and cultural conditions, they can thrive anywhere and will flower regularly.
These plants belongs to the Orchidacae family, with all the difference in size, shape, color, scent or lack of it. They are the most rapidly changing group of plants on earth with over 880 genera and 28,000 species.
Orchids have been considered a plant difficult to grow because of lack of knowledge about these fascinating plants. Taking a closer look at the plant will help us understand it better and take away our hesitation to nurture them in our gardens.
Basic Characteristics: Orchids are easily distinguished from other plants, as they share some very evident apomorphies. Among these, bilaterally symmetric (zygomorphic), many resupinate, one petal (labellum) is always highly modified, stamens and carpels are fused, and the seeds are extremely small.
Orchids belong to the most diverse family of plants known to man. There are over 880 genera, 28,000 species and well over 300,000 registered cultivars currently documented. These numbers only begin to tell the true story behind the evolutionary success of modern day orchids. Orchids are the most rapidly (genetically) changing group of plants on earth and more new species have been discovered over the last few thousand years than any other plant group known.
Orchids produce seed pods with literally hundreds of thousands of seed that are released and scattered by the wind. Orchid seeds must establish a symbiotic relationship with a special fungus to survive its first year of life. The fungi gathers water and minerals for itself and the seedling, and the seedling shares its sugars from photosynthesis with the fungus. Only one or two orchid seeds will ever germinate and survive on that perfect crevice or depression that is both moist and has the fungus present. Even then, its chances to survive in the wild long enough to bloom are slim.
Orchid Stem and Roots: All orchids are perennial herbs and lack any permanent woody structure. Orchids can grow according to two patterns: Monopodial and Sympodial.
Monopodial orchids have a central stem which grows continuously from the tip. They have no pseudobulbs, but produce new growth from the crown of the plant. Flowers are produced from the stem between the leaves, usually alternately from side to side.
Monopodial orchids often produce copious aerial roots along their stems. The aerial roots have green chlorophyll underneath the grey root coverings, which act as additional photosynthetic organs. These aerial roots attach themselves to any surface they meet, thus providing support to the plant. In the older parts of the roots, a modified spongy epidermis called velamen has the function to absorb humidity. It is made of dead cells and can have a silvery-grey, white or brown appearance. In some orchids the velamen includes spongy and fibrous bodies near the passage cells. These structures are named tilosomes.
Sympodial orchids possess a rhizome which sends out a shoot. This develops into a stem and leaves and eventually produces flowers. In time, from the base of this growth, a new shoot develops and so on in a continuous cycle. The buds are often, though not always, protected by a sheath.
Sympodial growth is more common among orchids. Most of these orchids have pseudobulbs which function as storage reservoirs for food and water. The plant will hold pseudobulbs vertically and send out new growth horizontally between the pseudobulbs. They function very much like rhizomes on terrestrial plants, although they are part of the plant rather than a root. The growth begins at the base of the pseudobulb and is called a “lead.” Both the shoot and roots will grow from this lead. Many times more than one growth at a time will be present. Leaves can last for several years and provide nourishment to the plant until they turn brown and die. Even without a leaf, the pseudobulb will continue to support the plant and provide nourishment for growth and flowering. Some sympodial terrestrials, such as Orchis and Ophrys, have two subterranean tuberous roots. One is used as a food reserve for wintry periods, and provides for the development of the other one, from which visible growth develops. In warm and humid climates, many terrestrial orchids do not need pseudobulbs.
With ageing, the pseudobulb sheds its leaves and becomes dormant. At this stage it is often called a backbulb. A pseudobulb then takes over, exploiting the last reserves accumulated in the backbulb, which eventually dies off too. A pseudobulb typically lives for about five years.
Comparison of Sympodial and Monopodial Orchid Growth Pattern
Orchid Leaves: Like most monocots, orchids generally have simple leaves with parallel veins, although some Vanilloideae have a reticulate venation. Leaves may be ovate, lanceolate, or orbiculate, and very variable in size. Their characteristics are often diagnostic. They are normally alternate on the stem, often plicate, and have no stipules. Orchid leaves often have siliceous bodies called stegmata in the vascular bundle sheaths (not present in the Orchidoideae) and are fibrous.
The structure of the leaves corresponds to the specific habitat of the plant. Species that typically bask in sunlight, or grow on sites which can be occasionally very dry, have thick, leathery leaves and the laminas are covered by a waxy cuticle to retain their necessary water supply. Shade species, on the other hand, have long, thin leaves.
The leaves of most orchids are perennial, that is they live for several years, while others, especially those with plicate leaves, shed them annually and develop new leaves together with new pseudobulbs, as in Catasetum.
The leaves of some orchids are considered ornamental. The leaves of the Macodes sanderiana, a semiterrestrial or lithophyte, show a sparkling silver and gold veining on a light green background.
The cordate leaves of Psychopsiella limminghei are light brownish green with maroon-puce markings, created by flower pigments. The attractive mottle of the leaves of Lady's Slippers from tropical and subtropical Asia, (Paphiopedilum) is caused by uneven distribution of chlorophyll. Also Phalaenopsis schilleriana is a pastel pink orchid with leaves spotted dark green and light green. The Jewel Orchid (Ludisia discolor) is grown more for its colorful leaves than its fairly inconspicuous white flowers.
Some orchids, as Dendrophylax lindenii (Ghost Orchid), Aphyllorchis and Taeniophyllum depend on their green roots for photosynthesis and lack normally developed leaves, as do all of the heterotrophic species.
Orchid Flowers: Orchids are well known for the many structural variations in their flowers. Some orchids have single flowers but most have a racemose inflorescence, sometimes with a large number of flowers. The flowering stem can be basal, that is produced from the base of the tuber, like in Cymbidium, apical, meaning it grows from the apex of the main stem, like in Cattleya, or axillary,
from the leaf axil, as in Vanda.
As an apomorphy of the clade, orchid flowers are primitively zygomorphic (bilaterally symmetrical), although in some genera like Mormodes, Ludisia, Macodes this kind of symmetry may be difficult to notice.
The orchid flower, like most flowers of monocots, has two whorls of sterile elements. The outer whorl has three sepals and the inner whorl has three petals. The sepals are usually very similar to the petals (and thus called tepals), but may be completely distinct.
The upper medial petal, called the labellum or lip, is always modified and enlarged. The inferior ovary or the pedicel usually rotates 180 degrees, so that the labellum, goes on the lower part of the flower, thus becoming suitable to form a platform for pollinators. This characteristic, called resupination occurs primitively in the family and is considered apomorphic (the torsion of the ovary is very evident from the picture). Some orchids have secondarily lost this resupination, e. g. Zygopetalum and Epidendrum secundum.
The normal form of the sepals can be found in Cattleya, where they form a triangle. In Paphiopedilum (Venus slippers) the lower two sepals are fused together into a synsepal, while the lip has taken the form of a slipper. In Masdevallia all the sepals are fused.
Orchid flowers with abnormal numbers of petals or lips are called peloric. Peloria is a genetic trait, but its expression is environmentally influenced and may appear random.
Longitudinal section of a flower of Vanilla planifoliaOrchid flowers primitively had three stamens, but this situation is now limited to the genus Neuwiedia. Apostasia and the Cypripedioideae have two stamens, the central one being sterile and reduced to a staminode. All of the other orchids, the clade called Monandria, retain only the central stamen, the others being reduced to staminodes. The filaments of the stamens are always adnate (fused) to the style to form cylindrical structure called the gynostemium or column. In the primitive Apostasioideae this fusion is only partial, in the Vanilloideae it is more deep, while in Orchidoideae and Epidendroideae it is total. The stigma is very asymmetrical as all of its lobes are bent towards the centre of the flower and lay on the bottom of the column.
Pollen is released as single grains, like in most other plants, in the Apostasioideae, Cypripedioideae and Vanilloideae. In the other subfamilies, that comprise the great majority of orchids, the anther, carries and two pollinia.
A pollinium is a waxy mass of pollen grains held together by the glue-like alkaloid viscin, containing both cellulosic stands and mucopolysaccharides. Each pollinium is connected to a filament which can take the form of a caudicle, like in Dactylorhiza or Habenaria or a stipe, like in Vanda. Caudicles or stipes hold the pollinia to the viscidium, a sticky pad which sticks the pollinia to the body of pollinators.
At the upper edge of the stigma of single-anthered orchids, in front of the anther cap, there is the rostellum, a slender extension involved in the complex pollination mechanism.
As aforementioned, the ovary is always inferior (located behind the flower). It is three-carpelate and one or, more rarely, three-partitioned, with parietal placentation (axile in the Apostasioideae).
Orchid Fruits and Seeds: The ovary typically develops into a capsule that is dehiscent by 3 or 6 longitudinal slits, while remaining closed at both ends. The ripening of a capsule can take 2 to 18 months. The seeds are generally almost microscopic and very numerous, in some species over a million per capsule. After ripening they blow off like dust particles or spores. They lack endosperm and must enter symbiotic relationship with various mycorrhizal basidiomyceteous fungi that provide them the necessary nutrients to germinate, so that all orchid species are mycoheterotrophic during germination and reliant upon fungi to complete their lifecycle.
As the chance for a seed to meet a fitting fungus is very small, only a minute fraction of all the seeds released grow into an adult plant. In cultivation, germination typically takes weeks, while there is a report of one paphiopedilum that took fifteen years.
The main component for the sowing of orchids in artificial conditions is the agar agar. The substance is put together with some type of carbohydrate which provides qualitative organic feed such as banana, pineapple, peach or even tomato puree or coconut milk. After the cooking of the agar agar, the mix is poured into test tubes or jars where the substance begins to jelly. The seeds have to be put in the dish above boiling water, in the steam because that secures sterile conditions. The test tubes are put diagonally after that.
Reproduction: Orchids have developed highly specialized pollination systems and thus the chances of being pollinated are often scarce. This is why orchid flowers usually remain receptive for very long periods and why most orchids deliver pollen in a single mass; each time pollination succeeds thousands of ovules can be fertilized.
Pollinators are often visually attracted by the shape and colours of the labellum. The flowers may produce attractive odours. Although absent in most species, nectar may be produced in a spur of the labellum, on the point of the sepals or in the septa of the ovary, the most typical position amongst the Asparagales.
In orchids that produce pollinia, pollination happens as some variant of the following. When the pollinator enters into the flower, it touches a viscidium, which promptly sticks to its body, generally on the head or abdomen. While leaving the flower, it pulls the pollinium out of the anther, as it is connected to the viscidium by the caudicle or stipe. The caudicle then bends and the pollinium is moved forwards and downwards. When the pollinator enters another flower of the same species, the pollinium has taken such position that it will stick to the stigma of the second flower, just below the rostellum, pollinating it. The possessors of orchids may be able to reproduce the process with a pencil, small paintbrush, or other similar device.
Some orchids mainly or totally rely on self-pollination, especially in colder regions where pollinators are particularly rare. The caudicles may dry up if the flower hasn't been visited by any pollinator and the pollina then fall directly on the stigma. Otherwise the anther may rotate and then enter the stigma cavity of the flower.
The labellum of the Cypripedioideae is poke-shaped and has the function to trap visiting insects. The only exit leads to the anthers that deposit pollen on the visitor.
In some extremely specialized orchids, like the Eurasian genus Ophrys, the labellum is adapted to have a colour, shape and odour which attracts male insects via mimicry of a receptive female. Pollination happens as the insect attempts to mate with flowers.
Many neotropical orchids are pollinated by male orchid bees, which visit the flowers to gather volatile chemicals they require to synthesize pheromonal attractants. Each type of orchid places the pollinia on a different body part of a different species of bee, so as to enforce proper cross-pollination.
After pollination the sepals and petals fade and wilt, but they usually remain attached to the ovary.
Gallery of Common Orchids
There are over 25,000 types of orchids and, in fact the Orchidaceae family is the most numerous in the plant world. These beautiful plants have been around for over 100 million years and plants can range from microscopic to reaching several feet in height. The flowers have a distinctive look with 3 inner petals surrounded by 3 outer petals and a cupped petal that is distinct from the others. Some orchids even resemble other creatures like bees, moths and lizards.
Although we think of orchids as a tropical flower they can actually grow in almost any climate. They can grow on the ground or on trees and even rocks. Orchids are classified depending on their water requirements. Paphiopedilum, Cymbidium and Odontoglossum need a moist environment all year long. Cattelya, Oncidium and Dendrobium only need water when they are actively growing and the vanda Ascocend doesn't really need water at all.
Below you will find pictures of some of the commonly found orchids. It is easy to identify them by their flowers.
Growing Orchids Tips for Beginners
Orchids have always been considered difficult to grow. Once the cultural needs of these fascinating plants are understood, growing orchids is relatively simple, and it becomes a deeply satisfying activity. If given the right climatic and cultural conditions, they can thrive anywhere and will flower regularly. Some species of orchids may flower two or three times a year and some flower annually.
The following is a brief guideline of the role of essential and beneficial mineral nutrients that are crucial for growth. Eliminate any one of these elements, and plants will display abnormalities of growth, deficiency symptoms, or may not reproduce normally.
Nitrogen is a major component of proteins, hormones, chlorophyll, vitamins and enzymes essential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth (vegetative growth). Too much can delay flowering and fruiting. Deficiencies can reduce yields, cause yellowing of the leaves and stunt growth.
Phosphorus is necessary for seed germination, photosynthesis, protein formation and almost all aspects of growth and metabolism in plants. It is essential for flower and fruit formation.
Tropical orchids are no more difficult to grow than other plants, but because most of them are epiphytes (tree dwelling plants) their culture is different from that of other types of plants. British orchid growers failed in the early 1800′s when they attempted to grow tropical orchids under dark, hot, and steamy conditions. They succeeded only when they realized that most tropical orchids grew at higher, cooler elevations and in the upper branches of trees where they got considerable light and perfect drainage.
In the greenhouse, most orchids require some shading to prevent the leaves from overheating. In the home, however, orchids need the maximum light available. Placing them outside under the shade of tall trees during the summer months is very beneficial. Do not place them in full sun, however, or the leaves will burn. Also, do not place the plants on the ground, for insects and slugs (snails) can enter the pots and damage the plants. Pot hangers can be used to suspend the plants from tree branches, chains, strong trees, or other structures.
In the home, placing the orchids in a room with relatively cool temperatures will help guard against dehydration. Most orchids are actually most happy at temperatures below the comfort level of humans, especially at night. Orchid greenhouses are usually maintained at 55-65 degrees at night.
Potting mixes for tropical orchids are loose mixtures of organic material such as fir bark (not pine bark), tree fern, osumda fiber, with small amounts of peat, perlite, cork, or charcoal added. The object is to have a mix that drains well, but holds some moisture. Most commercial orchid growers supply ready-to-use orchid mixes in small quantities. Orchids usually need repotting only once every two to three years.
In watering orchids, it is best to soak the potting mix thoroughly and wait until the surface is relatively dry before watering again. Most orchids in fir bark based mixes will need watering no more than once every 5 to 7 days.
All plants can be fertilized safely with a water-soluble urea free fertilizer such as Growmore 20-10-20 about once a month. Some orchid growers prefer to mix water-soluble fertilizers weaker than indicated on the package instructions and to use them every second or third watering. Always water before fertilizing and remember that it is best to under-fertilize rather than to over-fertilize. With the lower light and drier conditions in the home, orchids cannot use as much fertilizer as they can use in the greenhouse. Some growers like to increase the humidity around their orchids in the home by using “humidity trays” or trays of wet gravel around or under the plants. Pots should not touch the surface of the water.
One of the big mistakes that people make is over watering their orchids. People assume that since they are tropical plants they need a lot of water and this is not necessarily the case. While they do appreciate the humid environment, over watering can kill them.
The amount of watering necessary depends on the temperature any type of orchid a general rule of thumb is to water once a week. You may want to water more frequently in the summer and a little bit less in the winter. The Cymbidium, Miltonia, Odontoglossum and Paphiopedilum varieties like to be kept with the soil a bit moist even between wanterings while the Ascocenda, Vanda and Phalaenopsis prefer to have their soil become dry in between.
Which Orchid Plants Are Easy to Grow?
We have seen what orchids are and how to take care of them. The obvious question is which of these orchids can I grow at home, and which ones are easy to grow.
As a novice to the world of orchids, you only need to concern yourself with the name of the genus. Most plants within the same genus will require similar growing conditions, so if you want to keep things simple, don’t worry about the species or variety at this point.
Orchid Genera for the Novice
Novice orchid growers should start with members of the following genera, since these are relatively easy to grow orchids: Phalaenopsis, Paphiopedilum, Dendrobium, and Oncidium.
Phalaenopsis, or Moth Orchids, are one of the easiest orchids for beginners to grow, as well as one that is commonly found in stores. Members of this genus have multiple large, showy flowers on each spike; flowers that may remain open for six weeks or longer. Often when a spike is cut after its blooms are gone, a secondary spike will develop on the old stalk below the original flower head, thus extending the blooming season.
Phalaenopsis is a genus of approximately 60 species of orchids. The abbreviation in the horticultural trade is Phal. Phalaenopsis shows a monopodial growth habit. An erect growing rhizome produces from the top one or two alternate, thick and fleshy, elliptical leaves a year. The older, basal leaves drop off at the same rate. The plant retains in this way four to five leaves. If very healthy, they can have up to ten or more leaves. They have no pseudobulbs. The raceme appears from the stem between the leaves. They bloom in their full glory for several weeks. If kept in the home, they usually last two to three months, which is considered quite a long time. Some Phalaenopsis species in Malaysia are known to use subtle weather cues to coordinate mass flowering.
Caring For Phalaenopsis: In nature, they are typically fond of warm temperatures (20 to 35 °C), but are adaptable to conditions more comfortable for human habitation in temperate zones (15 to 30 °C). At temperatures below 18 °C watering should be reduced to avoid the risk of root rot. Phalaenopsis requires high humidity (60-70%) and low light of 12,000 to 20,000 lux. Flowering is triggered by a night-time drop in temperature of around 5 to 6 degrees over 2 to 4 consecutive weeks, usually in the fall.
Phalaenopsis prefer to be potted in medium fir bark. They can also be potted in sphagnum moss or mounted. Keep them in pots with a lot of drainage. Keep the potting media fairly moist but not wet. Water when the potting media is just approaching dryness, but still a bit moist and never allow the potting media to become bone dry. Do not let water flow into the center of the plant or it can potentially die from crown rot. One of the most numerous blunders that new growers make is to rot the roots. Overwatering and poor drainage cause the roots to deteriorate, therefore killing the plant. Being careful to water when you feel the soil is dry through and through is the safest thing to do.
Light is quite vital to the well-being of the phalaenopsis orchid. Keep it in indirect light near a southern window. Be sure the sun does not directly reach the leaves, which will cause burning and brown marks. If the leaf feels hot to the touch, move it away immediately. On the other hand, phalaenopsis grown in poor dark areas tend to grow floppy dark green leaves and rarely flower.
Phalaenopsis roots are quite thick, and the green point at the ends signifies that the root is actively growing. It is okay for them to climb out of the pots. Plant may be fertilized with a 1/4 diluted strength balanced fertilizer three times out of four waterings.
The flower spikes appear from the pockets near the base of each leaf. The first sign is a light green "mitten-like" object that protrudes from the leaf tissue. In about three months, the spike enlongates until it begins to swell fat buds. The buds will thus bloom. Usually you can tell what color the phalaenopsis is by looking at the bud color. After the flowers fade, some people prefer to cut the spike above the highest node (section). This may produce another flower spike or more rarely a keiki (a baby orchid plant that can be planted).
Paphiopedilum is a genus in the orchid family (Orchidaceae) of approximately 91 species.
Paphiopedilum, the so-called Venus Slipper orchid, is easily recognizable. Most have a single flower per stalk, but there are varieties with multiple flowers. They are relatively easy to coax into bloom if you provide the plant with the right temperature range: mottled leaves need warmer conditions than do solid green leaves.
Paphiopedilum (sometimes colloquially referred to as "Paphs") are considered highly collectible by growers due to the curious and unusual form of their flowers. Most naturally grow in humus layers as semi-terrestrials on the forest floor, in rocky outcroppings or in trees.
Caring For Paphs: Most paphs are intermediate growers and do well in medium to medium-high light. Most paphs should be kept evenly moist year-round. There are exceptions to these general guidelines, especially among the Chinese paphs some of which encounter winter temperatures near freezing, so it is important to research the cultural needs of a specific paph, especially if growing species. All paphs need a fresh environment and benefit from good air circulation and frequent repotting. The rule of thumb for paphs is to repot them every year, usually after flowering or in the spring so they can establish themselves before hot weather sets in. Paphs benefit from high humidity.
Dendrobium, abbreviated as Den in horticultural trade, is a large genus of tropical orchids that consists of about 1200 species. Dendrobium inflorescences are loaded with blossoms and are also long lasting. These plants can often be split when mature, since small additional offset plantlets are frequently produced. When an offset has produced several aerial roots, it can be cut from the parent plant and will frequently flower after one year of growth.
The species are either epiphytic, growing on a tree, or occasionally lithophytic, growing over a rock. They have adapted to a wide variety of habitats, from the high altitudes in the Himalayan mountains to lowland tropical forests and even to the dry climate of the Australian desert.
The orchids in this genus often develop pseudobulbs, which unite into a long reedlike stem with a typical length of more than 30 cm. Some appear densely covered with short white hairs. The short, ovate leaves grow alternately over the whole length of the stems. The axillary flower buds develop into short flower stalks with one or two terminal flowers. The orchids grow quickly throughout summer, but take a long rest during winter. In the spring, new shoots are formed from the base of the main plant and the dormant buds come back into action. The blooming flowers are found on pseudobulbs formed in the previous year.
Caring For Dendrobium: Care depends on specific species. Plants generally require a reduction of watering or with holding of water during the winter due to dormancy period. Plants grow in a variety of temperature ranges and lighting ranges which is dependent on the species. Plants can usually be mounted.
Oncidiums, commonly referred to as the "dancing girls" orchid, are also easy to grow. Abbreviated as Onc in horticultural trade, Oncidium is a genus that contains about 330 species of orchids from the subfamily Epidendroideae of the orchid family (Orchidaceae). Since this is a large genus with different species originating in a wide variety of climates, it is helpful to know the growing requirements of the particular species you select. Still, these hardy plants generally flower well even under adverse growing conditions.
The flowers of the Oncidium genus come in shades of yellow, red, white and pink. The petals are often ruffled on the edges, as is the lip. The lip is enormous, partially blocking the small petals and sepals.
Caring For Oncidium: Oncs grow in cool to warm conditions with moderate to bright light. Water the plant right before the potting mix starts to dry. Plants should be potted in a well drain medium such as medium fir bark.
Tips for Choosing a Healthy Orchid Plant
Orchids are found in a variety of climates, so choose an orchid that closely matches the growing conditions of your environment. This means assessing your light sources, available space, temperature range, and humidity.
Armed with this information, do a bit of research to find out which orchid plants match your environment. These will be the easiest types of orchid plants to grow and your success will encourage you to develop more skills as an orchid grower.
Although you can find orchids at supermarkets and home supply stores these days, it is still best to purchase one from a plant nursery where the plants will have most likely received specialized care. A nursery may also have an experienced orchid grower on staff, who can help you choose the best orchid for the temperature and light level in your home.
Orchid Leaves and Roots
Wherever you end up shopping for your orchid, be sure to give the plant a good once-over before you purchase.
Orchid roots are relatively thick and fleshy for storing water and nutrients. Ariel roots are also often visible above the growing medium. These are covered with a layer of white tissue, called velamen that acts like a sponge and protects the root from heat and water loss. The roots of the plant you select should appear firm and healthy, not dried up or rotted.
There are many leaf forms, depending on the type of orchid. An orchid may have thick, fleshy leaves, like Phalaenopsis, or thin elongated leaves, like Oncidium. Regardless of the leaf type, avoid plants that have yellowing or black-spotted leaves, which could indicate stress or disease.
Orchid Spikes and Blooms
When orchids bloom, most produce one or more flower spikes. These spikes are typically each an inflorescence composed of several flower buds that open first at the lowest point on the spike and progressively bloom to the tip (similar to how gladiolas bloom). The blossoms open over the course of weeks, and if the orchid has multiple spikes, the plant may bloom for months.
Choose a plant with multiple flower spikes and mostly unopened blooms. The gorgeous plants that are in full bloom at the store are nearing the end of their colorful show, and the blossoms will soon wither and die.
Orchid growing is one of the most satisfying hobbies in the world and is why it has remained so popular for more than 100 years. Empowered with the information that you have acquired here, you can go ahead and start your exploration into the world of orchids.
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