A Comparison of Various Methods of Classifying Three Genera of Orchids


Orchid Pictures


The purpose of this project was to investigate alternative methods of classification of three orchid genera (Encyclia, Cattleya, and Brassavola) using the light absorption spectrum of the chlorophyll to determine the boundaries of species.


It was hypothesized that a comparison of the chlorophyll light absorption spectrum will distinguish the species.
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Null Hypothisis

It was hypothesized that there would be no difference between the traditional method of classifying plants and the chlorophyll light absorption spectrum.
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Statement of Significance

The significance of this project is to use a new method of classifying plants to identify a plant.
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Index to Background:Taxonomy-Cattleya- Encyclia-Brassovola-General Orchids-Photosythisis


Plant taxonomy is the classification of plants. Taxonomy is built on a step ladder. It starts at Kingdom, which is the largest group, then it goes down to phylum, family, subfamily, tribe, subtribe, genus, species, and finally subspecies. Each group decreases in size until finally species consists of one plant or animal. The group subspecies is technically the most specific group and is determined by small changes or mutations in the plantŐs genetic makeup. It is sometimes caused by climate, temperature, light and availability of water. The plant tries to change or evolve to fit the circumstances.
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The orchid genus Cattleya has about 50 species. The name Cattleya was named after William Cattley, the first person to grow epiphytic orchids successfully. The inflorecense, or the flower spikes, rarely consist of more than 4 flowers. They are usually brilliant colors such as red, purple, white, and even rarely blue. The flowers can grow to be 8 inches in size. The plants are mostly epiphytic, meaning they grow in trees. They grow in hot to intermediate temperatures of about 55 degrees to 60 degrees F at night and temperatures of about 70 to 85 degrees F during the day. Most are scented. They grow in indirect light at about 3,000-5,000 foot candles. The roots cannot soak in water because they rot easily.
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The genus Encyclia consists of about 500 species that live in Central America, northern South America and the Caribbean. The flowers come in an array of shapes and colors. They are usually epiphytic with the exception of Encyclia cochleata, which is sometimes found as a terrestrial. This genus is a synonym to the orchid genus Epidendrum, meaning that most of the plants, sometimes all of the genus, can also be put under the name of another genus (in this case Epidendrum ). Changing the genus of the species takes off the "-a" and adds a "-um". Example: Encyclia maculosa would equal Epidendrum maculosum.

In the genus Encyclia, there are three basic flower color groups. In group one, the flowers are mostly green fading to yellow, (occasionally flowers have maroon speckles or spots) with darker color toward the base of the sepals and petals. Anthor caps of this group are usually white to yellow. The second group consists of flowers of the color brown tan to ochre. Many have a border of yellow or green. Lips are often cream color with brown to purple veining. The third group only consists of three or four species. The flowers are basically pink to purple.
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The orchid species Brassavola consists of about 30 species. Most Brassovolas are usually white and scented, such as Brassavola nodosa, which has the common name of "Lady of the Night" because it is fragrant at night. Brassavolas can vary in size and shape with some having petals 25 cm in length and some only about 8 cm in length.
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The Family Orchidaceae consists of about 35,000 species. Most are epiphytic, but are not parasitic, meaning they take nutrients from the trees. They only use the trees for support, and collect organic sediment around their roots from the rain. They have evolved to have a water storage organ called a pseudobulb. Orchids are the largest flowering plant family in the world, and live on every continent except Antarctica. Orchids were discovered by Theophratus, the father of botany. He named a European species of orchid Orchis because of its masculine underground tubers. The plants vary, from some that are no bigger than a thimble when fully grown, to some such as Vanilla planifolia that can grow up to 100 feet long. The flowers also vary in size from some that are impossible to see with the naked eye, to some flowers that are larger than a foot in size.

In the 1900's, humans found that the seeds of the orchid have no endosperms, which is the part of the seed that supplies the germ, or growth part of the seed, with food. Instead of using endosperms, they have a relationship with a species of fungus where the seed will feed off of the waste of the fungus. Later, Dr. Lewis Knudson found that people can replicate the complex sugars and starches that the fungus produces using simple sugars. To propagate by seed in a laboratory, they have to supply the seeds with sugar and vitamins. Later, in tissue culture media, a food mixture in an agar gel was invented. Then, Professor Knudson found that the meristimatice tissue of the orchid was culturable, meaning that the tissue could be made into more than one plant. Orchids are even eaten in the form of vanilla extract. Vanilla extract comes from the ground up pods of Vanilla plnifolia.

When people first started to grow tropical species of orchid they would use greenhouses attached to fireplaces. In 1835, for the first time, somebody actually grew a tropical orchid in a somewhat natural habitat. This English gardener had phenomenal results.

The roots of orchids are covered with a layer of microscopic hairs, called a velamen. They have many uses. Absorption of water is the main use. The velamen can pick up water in any weather, from a light fog to a heavy rain. The velamen is also used for protection of the softer inner area of the root. The velamen is very strong for gripping the side of trees, a pot, or any other object that will give the plant support.
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Photosynthesis is the process in which a plant uses light, carbon dioxide, and water to create sugars that it needs for growth. This procces is a photo chemical reaction, meaning it uses light. But, unlike many photo chemical reactions, heat can't be substituted for light. In photosynthesis, the roots bring up water from the ground and the leaves soak in carbon dioxide (CO2). CO2 is very soluble in water. Thus, the CO2 and H2O (water) combine into C6H12O6, or sugar. This process also creates six oxygen molecules (6O2) and is represented by the chemical equation:
6H2O+6CO2 = C6H12O6+6O2.

The process of photosynthesis uses a biochemical called chlorophyll. Chlorophyll is a photoreceptor, meaning that it traps sunlight to carry out a chemical reaction. Found in the cells of any green plant is something called chloroplasts. There are two types of chlorophyll, a and b , and they differ only slightly. The difference is in the composition of a side chain (in a it is -CH3, in b it is CHO).
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I Orchid Culture
1. Water every other day.
2. Allow to dry out between watering.
3. Fertilize with slow release fertilizer once a year.
4. Keep good air circulation.

II Extract Chlorophyll
1. Place about 1-3 grams of tissue into tissue grinder.
2. Put pestle into tissue grinder.
3. Fill with ethanol until tissue grinder is full.
4. Place a glass filter into tissue grinder.
5. Grind tissue until there is a bright green liquid.
6. Transfer liquid using dropper into centrifuge tubes.
7. Centrifuge for 1 min.

III Use Spectrophotometer
1. Transfer chlorophyll into a cuvette using droppers.
2. Place cuvettes into sample compartment of the Spectrophotometer.
3. Select wavelength.
4. Set mode to transmittance.
5. Adjust Zero Control until meter reads zero.
6. Insert reference blank into the sample compartment and set the Transmittance/Absorbency control to 100%.
7. Place sample into compartment and read absorbency from 340 nm.-750 nm.

IV Analyze Data
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The results of this project were conclusive.
Encyclia cochleata had peaks at 360, 380, 440, 460, 520, and 660 nm.
Encyclia tampensis had peaks at 340, 430, 660 nm.
Cattleya mendelii had peaks at 340, 430, 440, and 660 nm.
Cattleya labiata had peaks at 350, 430, 470, 560, 600, and 660 nm.
Brassovola nodosa had peaks at 390, 430, 440, and 660 nm.
Brassovola cordata had peaks at 360, 430, 470, 610, 650, and 700 nm.
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In conclusion, the hypothesis was accepted. A comparison of the chlorophyll light absorption spectrum will distinguish the species.
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American Orchid Society. Orchids A to Z. [Online] Available at www.theaos.org/orchids/az/(accessed on Nov. 27, 2001).
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Hodgson, M., et al (1991). A Guide to Orchids of the World. New York, HyperCollins Publishing.

Kaskel, A. (1985). Biology an Everyday Experience. London. Charles E. Publishing Co.

May, P. Chlorophyll. [Online] Available at http://www. tlchm.bris.ac.uk/motm/chlorophyll/chlorophyll_h.html. (accessed on Oct. 28, 2001).

Schuler, S. (1988). Orchids. London. Simon & Schuler.

Science Service. (2001-2002). International Rules for Precollege Science Research: Guidelines for Science and Engineering Fairs. Science Service. Washington, D.C.

Silverstein, A., et al . (1996). The Kingdoms Plants. Brookfield. Twenty-First Century Books.

Transean, E.N. et al. (1940). Textbook of Botany. New York. Harper Brothers Publishing.

Marden, L. (1971). Exquisite Orchids. National Geographic. 139 (4).

Withner, C.L. (1996). The Cattleyas and Their Relatives. Portland. Timber Press.

Withner, C.L. (1988). The Orchids, a Scientific Survey. Malabar. Robert E. Krieger Publishing Company.

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