by Jared "Flash" Fogel

Classification/Diagnostic characteristics

Orchid Anatomy (8) (SJ)

Orchids describes the orchid family or Orchidaceae that contains over 25,000 of orchids and over 800 genera. They are very well-known for their many structural variations in their flowers, many of which are very beautiful.

Classification: Domain: Eukaryota; Kingdom: Plantae; Phylum: Angiosperm; Class: Monocots; Order: Asparagales; Family: Orchidaceae

Darwin's explanation of three distinct orchid flowers growing on a single orchid plant was that the orchid is a single species called Catasetum macrocarpum that bores three distinct types of flowers: megasporangiate (female), microsporangiate (male), and perfect (hermaphroditic). Also that the three types of flowers have noticeable morphological differences. However, it is now known that Catasetum is only genus one of the many hundreds and macrocarpum is only one species of the many thousands in the orchid family.

Chart of different types of orchids. (LC)
Chart of different types of orchids. (LC)

Relationship to humans

Darwin used the pollination of orchids to help explain his ideas about the mechanisms of evolution. Orchids showed that aspects flowers such as coloration and form evolved in response to natural selection. His book, Fertilisation of Orchids, came out in 1862, three years after The Origin of Species. In the book, Darwin examined why orchids experience such rapid diversification as well as the role of insect pollinators in this process. Orchids gave Darwin an adundance of examples for his research on the power of natural selection.

For years, humans have been obsessed with raising these beautiful flowers. Specifically in the early 1860's in England, much of the middle and upper class were caught up in an "orchid frenzy" in which amateur plant breeders and professional botanists were all racing to grow orchids. Both the scent of orchids for perfumes as well as the beauty of orchids for enjoyment as ornaments are the two main purposes that orchids serve in their relationship with humans.

Other than its use as a beautiful flower and appealing scent, there is one commercially important product that is derived from an orchid: vanilla. Vanilla planifolia is the primary source used for vanilla but the species V.pompona and V.tahitensis are also used. The vanilla orchid is the only fruit bearing orchid of the orchid family, and it produces vanilla pods (what we know as vanilla beans). These vanilla orchid growing areas include Madagascar, Meixco, French Polynesia, Indonesia, the West Indies, and Puerto Rico, although they originated in Mexico. Interestingly, when Cortez brought Cacoa beans back to Spain he also brought with him vanilla pods. (7) (PS)
Vanilla planifolia - (14) (WSS)

Habitat and niche

Orchids usually live in nitrogen-poor habitats and are common in tropical areas of the globe. The world's richest concentration of orchid varieties are found in Asia, South America, and Central America. Orchids can grow from the ground, or hang from the branches of trees.
Orchids that grow on trees are called epiphytes, and do not actually take anything from the trees they are growing on but just grow on it to be closer to the sun.3(BS)
Orchids have adapted to a range of different biomes, although some have more than others. Savannas and grasslands don't feature many orchids, but islands, lowland swamps, and other tropical areas, often feature a large number of orchid species. (TM)

Predator avoidance

Orchids employ mimcry, a method disguising or misleading themselves to be a different species Using chemical mimcry, orchids will emit a sex hormone of a particular wasp species, so that promiscuous male wasps will try to mate with the 'female wasp,' but instead pollinate. Similarly orchids emit pheromones, a chemical that causes a social response, that mimic aphid alarm pheromones, attracting hover flies to eat predatory aphids. (AWC)[1]

Nutrient acquisition

Orchid seeds will almost always not germinate in nature unless they are infected by the fungus that will form their mycorrhizae, which they often share with the roots of green, photosynthetic plants. Thus, orchid plants, though they lack chlorophyll, feed on nearby green plants for nutrients using fungus as a bridge. The fungus contact the orchid roots and exchange nutrients, mainly carbon and nitrogen. Many orchid species cannot survive without their fungus partner. Orchids will continue to rely on their fungi partner for nutrients unless they develop leaves and are able to utilize gas exchange, but some orchid plants never devlop these and rely on fungi their whole life. The fibrous root system of orchids usually has a large surface area that is key for the absorbtion of water and minerals.

Reproduction and life cycle

Orchid that looks like a female bee, attracting other bees to come pollinate it. (10) (AA)
Orchid that looks like a female bee, attracting other bees to come pollinate it. (10) (AA)

Insect pollination plays a significant role in orchids' rapid diversification. Orchids have a strong variety of specialized pollination mechanisms, such as the South American orchid of the genus Catasetum which shoots a packet of pollen at an insect that lands on its flower. The Angraecum sesquipedale, an orchid from Madagascar has a nectar tube over a foot long for a moth with an extremely long proboscis. The pollinia/pollen packets and associated structures in male flowers of Catasetum are coiled like springs and are released quickly when an insect disturbs the flower. The pollinia is forcefully released onto the back of the insect. The insect pollinator of Orchids is a specific bee species, of which the males are attracted to the odor of the flowers. Although the flowers give no nectar to the bees, the male bee obtains a the chemical that produces the scent. When the bee visits another female flower on another orchid, there is no "loaded spring" awaiting the bees arrival. The morphology of the female flower enhances the removal of the pollen packers from the bee's body; thus, the floral morphology increased the chances of cross-fertilization opposed to self-pollination.
The orchid depends on like butterflies, wasps, or bees. Because the orchids have unique shapes, it attracts insects to copulate with it and leaves pollen on the insect.(9)(NC)
The Orchids reproductive organs are combined into a structure called the gynostemium, this structure is a big identifier for the orchid. At the top of the gynostemium is the pollen packets and at the bottom is a sticky area where the pollen can be fertilized. (ES)

Growth and development

Triploid endosperm is produced during the the life cycle of most angiosperms; however, orchids lack an endosperm around their embyro. Like all seed plants, orchids are heterosporous, and their ovules are contained within carpels rather than being exposed on the surface of scales. Male gametophytes are the pollen grains that find their way to pollinate another flower. When pollination occurs, the zygote develops into an embryo, which consists of an embryonic axis and one cotyledon (seed leaf). Because orchids are angiosperms, the ovule devlops into a seed containing the products of double fertilization. During germination, orchids have a single embryonic cotyledon that becomes the embryonic first leaves of the seedling. Although orchids have many structural differences, the majority will follow the root and shoot systems constisting of the stems, leaves and flowers. The root system originates in a short-lived embryonic root called the radicle. Monocots form a fibrous root system composed of many thin roots that originate from the stem at ground level.

Orchids can be either monopodial, meaning one stem grows from a single bud and leaves grow from the apex with the stem growing accordingly, or sympodial where a few stems grow, they bloom and then die. (6)(BH)

There are three types of flowers:
Catasetum (flowers with male parts)
Monachanthus (flowers with female parts)
Myathus (flowers with male and female parts)


Very few orchids will have a endosperm coat around their embryonic sporophyte as they form and sprout to become a plant. However, the ovules and seeds of orchids are enclosed in a modified leaf called a carpel. Carpels serve as the outer-protection for the ovules and seeds, and they often interact with incoming pollen to prevent self-pollination, favoring cross-pollination and genetic diversity.


Orchid plants are stationary and are unable to move to find a more suitable environment or to avoid predators. They are anchored to a single spot by their roots and stem.

Sensing the environment

Contrary to popular belief orchids as well as all plants do in fact sense the environment despite the fact that they have no nerves. Orchids can tell the direction and quality of light and use this information to grow advantageously. They sense temperature as well. Orchids bloom at the right time, because they can sense the temperature, and humidity of their environment, and bloom when they find the environment suitable to. Many gardeners try to use these senses to their advantage in order to get orchids to bloom when they want them to. (MDS) (12,13)

Gas exchange

Unless the orchid has built chlorophyll and is able to utilize photosynthesis, taking in carbon dioxide and water and producing oxygen and sugar, they are completely dependent on their fungi partner for their nutrients in life. Initially, all orchids are unable to maintain gas exchange, yet as they develop leaves they are able to use photosynthesis.

Orchids exchange gas through their stomata under the leaves like most leafy plants. During the day, they are used as a means to absorb and release oxygen, carbon dioxide, and water vapor while photosynthesis occurs. At night the stomata close in order to undergo respiration. (15) (DM)

Waste removal

Orchids remove their waste through photosynthesis in the form of oxygen and sugars.

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. [2] (CC)

Environmental physiology (temperature, water and salt regulation)

Orchids require about a 15 degree temperature difference between night time low temperatures and day time high temperatures. Obviously in their natural environment this happens naturally. Orchids need this temperature variation in order to store food.
In addition there should be a difference of about 20 degrees in temperature between day time high temperatures of winter and summer. The orchid plant needs this temperature variance to determine what season it is. (5) (MC)

Most plants open their stomata during the day and close them during the night, losing a lot of water in the process. To prevent water loss, certain species of orchids use CAM, or Crassulacean acid metabolism, photosynthesis. Instead of opening their stomata during the day, orchids open them during the night, allowing them to uptake carbon dioxide and store it as an acid without losing as much water. Then, during the day, the stomata close and the plants break down the acid, releasing carbon dioxide for photosynthesis. This allows certain species of orchids to conserve water because CAM photosynthesis only allows to escape during the night when it is cooler. [3] (FZ)

Internal circulation

Orchids take in water and minerals from their roots as well as carbon dioxide from their leaves. Water and minerals travel through the stem of the plant to the leaves. All of these nutrients are processed in the plant and oxygen and sugar are released through photosynthesis.

Orchids are vascular plants and therefore utilize the xylem & phloem transport system. Xylem and phloem are two different types of tissue which work as transport pathways for materials. The xylem transports water and minerals from the roots of the orchid in the soil up through the stems and distribute the water and minerals to the other organs. Likewise, phloem carries glucose, the orchid's food made from photosynthesis in the leaves, to the other organs in the plant. The two tissues work in opposite directions; phloem generally works top to bottom while the xylem work from bottom up. [11] (AY)
(16) (DA)

Chemical control (i.e. endocrine system)

  1. ^ http://rspb.royalsocietypublishing.org/content/early/2010/10/06/rspb.2010.1770.full
  2. ^

  3. ^


1. Hillis, David M. Principles of Life. Sunderland, MA: Sinauer Associates, 2012. Print.
2. http://sweetchicevents.com/blog/meet-the-flowers-orchids/cymbidium-orchid-wedding-flower-pink/
3. http://urbanext.illinois.edu/hortihints/0204d.html
4. http://www.ctu.edu.vn/~dvxe/Hoa%20Lan/Doc%20on%20web/Orchid%20Anatomy.htm
5. http://www.onlineorchidcenter.com/orchid-care-and-temperature/
6. http://myorchidcare.com/orchid-care/Orchid-Growth-Patterns.html
7. http://www.britannica.com/EBchecked/topic/431285/orchid/73081/Economic-importance
10. http://webecoist.momtastic.com/wp-content/uploads/2010/02/bee-orchid.jpg
11. http://www.cliffsnotes.com/study_guide/Vascular-Plants-Described.topicArticleId-8741,articleId-8672.html
12. http://news.softpedia.com/news/The-Sense-of-the-Plants-84523.shtml
13. http://www.gardeners.com/Getting-Orchids-to-Bloom-Again/7241,default,pg.html
14. http://elkinvanaeon.net/Alchemy_II/Herbs/Vanilla.htm
15. http://www.eoearth.org/article/Stomata?topic=49510
16. http://thomson.fosterscience.com/Biology/Unit-ProtistsFungiPlants/SeedPlantsNotes.htm

Review Questions
1. The majority of orchids follow what system consisting of stems, leaves, and flowers? (JLev)
2. What is the most major difference, in terms of pigmentation, between orchids and other plants? How do orchids compensate for this? (E.S.S.)
3. What are the three types of orchids and what distinguishes them from one another? (BB-V)
4. Describe the relationship some orchids have with fungi. Why is this biological relationship so important for the survival of the plant? (KG)
5. How are the systems of orchids similar to the systems of moss? (JLau)
6. How is the South American orchid pollination mechanics different from other orchids and flowers? (SM)
7. Name an example of how the orchid senses the environment and what it does with the information it gets from sensing it. (MDS)