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| Fucus a member of the Phaeophyta |
Science is an organized attempt to use our mental and physical faculties to understand the Cosmos.
The first step in this process is identification & classification.
 Spirogyra a filamentous member of the Chlorophyta (Green Algae) |
 Ulva (Sea Lettuce) is a multicellular member of the Chlorophyta. |
 Pallavicinia is a member of the Bryophyta. |
All of these organisms have the same Photosynthetic Pigments but they differ in structural complexity and other traits that are not apparentfrom these images. Spirogyra is a fresh water organism while Ulva is a marine species. Both are members of the same Division (Chlorophyta). Pallavicinia is a terrestrial species that superficially resembles some Chlorophyta. However it belongs to the Division Bryophyta. |
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All human cultures have striven to identify and organize biota into categories. Hawaiians have their own system of plant identification.
Plants that grow in the ocean can be separated from land plants based on their habitat.
They might be separated on the basis of Color, Structural Complexity or Motility
Traits used to separate organisms can also be used to group them.
Some traits may be better for classification than others!!!!!!!
What are the similarities and dissimilarities of the two organisms below?
 Ulva (Sea Lettuce) a member of the Chlorophyta that lives in the ocean. |
 This a "filmy fern" leaf from a member of the Pterophyta. It grows on land but it must be continuously moistened in order to survive |
| Ulva is an aquatic plant. Ulva is Marine and lives in salt water. Ulva has the same pigments as Ferns Ulva is only two cells thick
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Filmy Fern is semi-aquatic. Filmy Fern requires fresh water.
Filmy Fern has unicellular areas but it is basically multicellular. Filmy Fern has Organs (Root, Stem Leaf) |
The differences between terrestrial plants and animals are readily apparent as are the major differences between Elephants and Ants, or Royal Palm and a Moss.
However, the more we learn about the complexity of living organisms the greater is our ability to accurately group and separate species that appear similar.
The invention of the light microscope & the electron microscope revealed new worlds of living things and provided finer criteria for classification.
| Euglena (Euglenophyta) Cell seen with a Light Microscope |
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| Ulva (Chlorophyta) Motile Cell viewed with an Electron Microscope |
The emergence of Biochemistry & Molecular Biology have provided new, powerful ways to classify organisms.
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