• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

What is so special about the Orchidaceae?

Extracts from this document...

Introduction

What is so special about the Orchidaceae? Orchids have captured man's interest since the dawn of time. They display diversity unparalleled within the plant kingdom and are regarded as the most complex plants, both in structure and function. Orchids are spread throughout the whole world, from the Arctic to the Antarctic and every habitat in-between. There are about 35,000 species over 500-600 genera, making them the largest family of the angiosperms, in fact, 1/7th of the total number of angiosperm species belong to this family. The name "orchid" comes from the Greek philosopher Theophrastus, the father of botany, who commented on how the unusual paired roots of a plant looked like a pair of testicles or in Greek "orchis". Interestingly it was thought that the flower was able to "invoke Venus" and allow the parents to choose the sex of their child, a practice that continued into the middle ages. The characteristics and relative importance may not be apparent at first, they are herbaceous perennials, like many other plants, but their diversity comes not from one specific characteristic but from a whole range that integrates into the plants form and function. Orchids, as stated before, are found all over the world in many different habitats. The temperate zone orchids, like the ones found in the UK are all terrestrial, but the Tropical and Sub-tropical species are nearly all epiphytic. The term epiphytic means that the plant isn't bound to the substrate, it actually lives on another plant. It is not to be confused with parasitism though as the host plant does not come to harm through this relationship. ...read more.

Middle

As we continue moving up the plant we see the next adaptation that makes the orchids so special is the development of the flower. When in bud form the labellum, the modified petal, is above the other two petals, yet when the flower opens it is below them. The bud actually twists on its axis in a process known as resupination. The flowers align their labellum according to gravity so the twist may not always be a whole 180o, for example, the flowers of the genus Cymbidium all align so their labellum is facing downwards, no matter what the orientation of the flower originally was on the branch. The evolutionary reason for this odd process of twisting is unsure, but it is thought that in some flowers this facilitates the use of the labellum as a "landing pad" for insect pollinators. In fact most species of orchid have ultra violet markings on their labellum to act as landing lights for insects that can see into the UV spectrum. Although not all species of orchid rotate their labellum at one point in time they did and it is considered a basic feature of the family that has been lost by some species. Those species may not resupinate at all or some may in fact hyper resupinate, where selection originally favoured the non-resupinate flowers and they compensated for this by extending their twist to a full turn. This type of behaviour is seen mainly in some species of Malaxis. However the characteristic that makes all orchids so special is their flower. ...read more.

Conclusion

The flowers of Oncidium, when moved by the breeze, resemble a male Centris bee flying. These bees are highly territorial and another male will swoop in and sting it, the flower then deposits its' pollen on it as it fly's away. Another form of insect mimicry is called pseudocopulation, where the flower looks like a female insect. As the male tries to mate with it pollination occurs. What is remarkable about this is that the mimicry can be so exact even the surface texture is reproduced, and that it has evolved separately in orchids in completely different parts of the world. Example of pseudocopulation mimicry in the Mediterranean orchid Ophrys Summary The Orchidaceae are an incredibly successful and special family and their adaptability has allowed them huge speciation. The main points we covered in this essay regarding what makes them so special are. 1. Their stamen are all on one side of the flower, not symmetrically arranged like most angiosperms and the majority of orchids only have one. 2. The stamen and pistil are completely united into the column. 3. Tropical species are all epiphytic. 4. Their seeds are tiny and numerous. 5. The presence of the velamen. 6. The flower has a modified petal known as the labellum. 7. Resupination occurs in most species. 8. The existence of pollinia 9. Their ability to adapt their flower to attract a wide variety of pollinators. As you can see the reasons why they are so special are numerous, but many orchids are under threat from deforestation and loss of habitat. It is vital if we are to learn more about their diversity that we make every effort to conserve them. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Living Things in their Environment section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Living Things in their Environment essays

  1. Marked by a teacher

    In this experiment, mung bean seedlings and Brine shrimp eggs were used to study ...

    4 star(s)

    The total number of eggs in observation was counted. Then, the number of eggs hatch, the number of shrimps that were alive and the mobility of shrimps were observed and counted. The percentage was obtained by dividing them with the total number of eggs in observation. At the end of the three day, it was found that the number

  2. Marked by a teacher

    biology instinctive behaviour

    3 star(s)

    Each of the forms of human entertainment that employ animals have specific inherent cruelties: * The circus . . . Circus animals live in trucks or in chains when not performing tricks in the ring. Most people, seeing tigers jumps through hoops of fire, or elephants stand on their heads, never think about what is behind the scenes.

  1. What Factors are responsible for the success of Insects?

    can actually freeze up to 90% solid and then thaw out without incident (Berenbaum, 1995). Behaviour Organisms must be capable of recognising and responding to environmental differences, to make best use of it. Insects have developed more highly advanced sensory and neuro-motor systems than most other invertebrates, perhaps comparable with those of lower vertebrate animals (Gullan & Cranston, 1994).

  2. The comparison of bacterial content in a range of milks.

    This has improved my aseptic techniques for microbiology. (The preceding techniques require the use of special culture dishes named petri dishes or plates after their inventor Julius Richard Petri.) The most efficient method of culturing the bacteria would be the spread plate technique.

  1. Evolution, Natural selection and Darwinism

    Inbreeding: When, by chance, a variety of plant or animal arose which possessed some useful character, it was bred with its close relatives in the hope of retaining the character for future generations. Inbreeding is used widely especially for dogs and cats.

  2. Branded Bleach is more effective at killing E. coli than Non branded bleach - ...

    This is due to time constraints in the real experiment at least fifteen runs can be taken with both bleaches at each concentration. Also as bleach itself is a very effective oxidizing agent it will kill a large volume of the bacteria meaning when concentrations are highest it becomes difficult to derive accurate values for the zones of inhibition.

  1. At the end of 1996 the IUCN announced that 33,730 species of plant are ...

    The most important additional advantage is that it is non-toxic to mammals and plants, and is biodegradable (unlike DDT). Acacia trees also release toxic chemicals in response to predation from giraffes - a pheromone is released (via a reaction mechanism) that causes all surrounding trees to produce this chemical too.

  2. Where are all the bees?

    Why are bees dying? In most cases this is largely due to loss of wild habitats, intensive farming and overuse of pesticides and herbicides.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work