Orchid (angiosperm)

Aashna Narang



1.Classification/Diagnostic characteristics
An orchid is classified as an angiosperm, or a flowering plant. The orchid's most distinctive characteristic is its flowers; the blossom consists of an outer whorl of three sepals and an inner whorl of three petals. The outer petals, also known as the dorsal sepals, often often form a "hood", which shields the interior reproductive sections of the [[#|flower from]] being damaged by weather. The middle petal, called the labellum, develops into a decorative platform that is designed to attract pollinating insects. (2) [GW]

external image orchid+anatomy.jpg
This image shows the structural anatomy of the orchid as described above.

The roots and stems of orchids can grow according to one of two patterns:
-Monopodial: The stem grows from a single bud, and leaves are added from the apex each year.
-Sympodial: The plant produces a series of adjacent shoots which grow to a certain size, bloom and then stop growing, to be then replaced.

wx.png2.Relationship to humans
Orchids have shown a long history with humans with scientists such as Charles Darwin and Robert Schomburgk, who studied them for their behavior and reproduction methods. They are now mainly grown as ornamental plants for gifts or home decorations.

One type of orchid, the vanilla, derives the commercial vanilla flavoring. It is widely used for food [[#|and cosmetics]]. The most common vanilla orchid is the flat-leaved vanilla, or Vanilla planifolia. [[#|Vanilla orchids]] have been used since the 16th century when the Aztecs first discovered the orchid, lured by its exotic aroma. It has since been widely used for flavoring foods and beverages, and also has been used as an aphrodisiac and for therapeutic values (ie. aiding digesting, preventing headaches, counteracting poison bites).
http://www.clanorchids.com/culture/vanilla.html (BHu)

3.Habitat and niche
These plants live in nitrogen-poor habitats. They are unsurprisingly grown in the soil and watered often in domestic environments, such as households and gardens. [1] In nature, orchids are found throughout the county, from coastal shores to herb fields in the alpines. Most species favor soil with relatively poor nutrients and little drainage. Orchid habitats include forests, scrublands, and swamps. (2) [GW]

Since orchids are epiphytes, the roots are designed to be exposed to the environment. The ideal mix retains adequate moisture without becoming saturated and allows plenty of drainage and support. Even terrestrial orchids keep their roots in upper layers of soil to maintain proper gas exchange and water penetration. It seems that orchids can be raised in about anything including rock, glass, clay, pellets, and perlite.
Epiphytes, or air plants, grow everywhere but can be found mainly on the branches, trunks, and even the leaves of trees.

orchid habitat.jpg

The amount of light that is required depends on the species of the orchid. Regardless of the species, they do not like too much or too strong sun light. Many orchids do best facing the eastward direction. Naturally found orchids typically are found in tropical conditions where they receive both shade and sun. Orchids that suffer from either sun exposure that is too strong or being in the sun too much will start to show yellowing in the leaves. Many species of orchids grow best in cold conditions; however, there are several species that grow very well in room temperatures between 75 and 85 degrees Fahrenheit, with the proper amounts of air, fertilizer, light, and water.
Taken from the website:

4.Predator avoidance

Because the Orchid is a plant and does not have any attack mechanisms that can prevent predator attacks, it does not have a predator avoidance system. (evan) (http://www.merklesorchids.com/CulturePgs/whatsanorchid2.htm)

Although orchids cannot formally defend themselves from predators, they produce seeds and can pollinate. These two reproductive mechanisms allow orchids to proliferate and thrive in more environments. An abundance of orchids lessens the chances of an enemy wiping the species clean of the area.
http://www.merklesorchids.com/CulturePgs/whatsanorchid.htm (BHu)

5.Nutrient acquisition
Due to the fact that they live in habitats that are lacking in nitrogen, they have mycorrhizae, or an association that develops when a plant's root system becomes infected with fungi. This helps the plant acquire the nutrients it needs to by feeding off other plants. [1]
Mycorrhizae are a bacterial fungi that live mutualistically among the roots of many plants, including orchids. Particularly of the ectomychorrhizae variety, the fungus forms a protective sheath around the roots of orchids, forming pockets in soil, they help with aerating soil and water absorption as well as providing nutrients like nitrogen. They are also fundamental during germination, a time when the orchid has no energy reserves and depends entirely upon the fungus for food.

Like all plants, orchids and angiosperms use photosynthesis as their main process of nutrition, taking water and nutrients through the roots, while taking carbon dioxide (CO2) from atmosphere, and sunlight through its chloroplasts, using the energy to create glucose and ATP from its uptake.

irc.png6.Reproduction and life cycle
Orchids have perplexing reproduction patterns. They undergo rapid diversification due to pollination by insects. They demonstrate three types of flowers on one plant that have male and female parts as well as perfect flowers that have both.
When an insect lands on them, pollen is thrust toward it by one of the flower's male parts. After that, the insect travels to the female part of another flower and the pollen rubs off onto it. This contributes to the diversity as most flowers are not self-fertilized.

The male gametophytes, referred to as the microgametophytes, are produced in the anther sacs in the anthers of the flower’s stamens. The gametophytes correspond to the stages in a plant’s life cycle that can produce mature sexual reproductive cells, such as sperm and eggs. The sperm are encased in a protective cover called the pollen grain that gradually diminishes as the microgametophyte matures, leaving behind a two-celled male gametophyte. The female gametophytes, referred to as the macrogametophytes, are produced in the ovary of the flower. The ovary is composed of one or many carpels that contain ovules, or immature seeds. The entire female reproductive structure, including the ovary, is collectively known as the gynoecium. Along with the ovary, other structures in the female reproductive system are the stigma, a sticky surface where airborne pollen grains adhere, and the pistil, a long tube leading from the stigma to the ovary’s inside. When the pollen is mature, it is released for dispersal. Upon binding to the stigma, one of the two cells of the pollen grains pushes its way down the pistil to the ovary, forming a pollen tube, while the other cell, the sperm, follows to fertilize the ovule once it reaches the ovary. The newly formed fertilized ovule contains the developing zygote, which grows and differentiates into an embryo. When the seed is mature, it is released from the ovary and begins to germinate and grow once it finds a fertile growing location. (Alexander Soloviev)




7.Growth and development
The orchid's growth and development has interested the aforementioned scientists and many others due to their ability to sprout three different types of flowers on one plant. There are three types of flowers: [1]
- Catasetum (flowers with male parts)
- Monachanthus (flowers with female parts)
- Myanthus (flowers with male and female parts)

The orchid has a protective structure that originates from base of an ovule and encloses it almost entirely except for an opening, the micropyle, at the tip of the nucelllus. The orchid has two integuments that protect its structure.
http://botanydictionary.org/integument.html (Cam)

These plants do not move other than towards sunlight (phototropism) or simple growth.

10.Sensing the environment
Phototropism as mentioned above.

11.Gas exchange
They have a fairly limited amount of gas exchange through their leaves because they have to hold moisture in for long periods of time. Therefore, much of this activity is done by the roots

12.Waste removal
Like most plants with leafs, orchids rid themselves of extra oxygen produced during photosynthesis by allowing it to diffuse out of stomata on the leaves, or out of the roots systems. The orchid generally keeps its stomata closed to conserve water, and waste gases are usually released at night, when triggered by less light intensity on the plant.
external image orchid+root+section+edit_edited-1.jpgMicroscopic view of an Orchid Root
13.Environmental physiology (temperature, water and salt regulation)

The stomata is key for sensing and adapting to the enviornment. It opens and closes in reaction to CO2 and O2 levels, temperature, water availability, etc and controls the amount of gas exchange at a given point of day depending on these factors. (http://jxb.oxfordjournals.org/content/62/8/2419.full)

14.Internal circulation
Angiosperms have vascular bundles in which xylem and phloem form concentric rings. The xylem transport water and minerals via transpiration, and the phloem transport the products of photosynthesis.
external image plantbod.gif

15.Chemical control (i.e. endocrine system)

In angiosperms, flowering is caused by the release of the hormone gibberellin, which signals for the plant's floral meristem to develop and create the components that eventually will become a flower. (Colin Gray)

Review Questions:

1. How do plants get rid of the excess oxygen in their systems from photosynthesis?
2. What are the three different types of flowers and what sets them apart from one another?
3. Why did Charles Darwin choose orchids to study?


1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life. Sudnerland, MA: Sinauer [[#|Associates]], 2012. Page 479, 864
2. http://www.teara.govt.nz/en/orchids/1