Connecting the environment of the ancient past with the natural and cultural history of yesterday and today.















 

 


Green Planet: The History of Land Plants

Exhibit prepared by Dr. Taylor W. Taylor

Head, Department of Biology

Indiana University Southeast

New Albany, Indiana

Acknowledgements:

 

Green Planet: The History of Land Plants was developed by Dr. David Winship Taylor, Indiana University Southeast, and Alan Goldstein, Falls of the Ohio State Park.  We would like to thank the following for loans of material for the display and permission to use images for this web exhibit.

  • Indiana State Museum
  • The Children’s Museum of Indianapolis
  • Indiana University Southeast
  • Anonymous private collection

How long have green plants been around?

 

Display case #1 title: Invasion of Land: Leading the way for animals

 

What living plants are most similar to the oldest vascular plants?

 

Many of the oldest fossils are unlike any living plants and are extinct species.  The first fossils that are similar to living species are members of the lycopod group.  They have branches that evenly forks and small simple leaves.

 

Why are nonvascular plants rare and poorly preserved?

 

Although the evolutionary tree based on DNA suggests that nonvascular plants should be the oldest green plants in the fossil record, they are rare and poorly preserved.  As you can see the living representatives do not have parts that preserve easily.  Recent studies have clearly shown fossil remains similar to nonvascular plants, but diagnostic details are difficult to see. 

 

Why do plants appear on land before animals?

 

Until the Ordovician, the oxygen levels in the atmosphere were relatively low.  Because of the low level of oxygen, it is assumed that the ozone layer was not fully developed and that high levels of ultraviolet radiation would have prevented any life from surviving on land. 

 

Although nonvascular plants are not well preserved, cuticles and spores are resistant to decay. They appear in the fossil record first, later followed by mega-fossils of probable nonvascular plants.  Definitive vascular plants appear by the mid-Silurian and are easy to identify because of the decay resistant parts such as vascular tissue.

 

Animal parts are not found in land sediments until the Upper Silurian about 418 million years ago.   Since arthropods either eat plant parts or eat other animals that eat plant parts, there was no food for them on land until plants invaded.   This began the first terrestrial ecosystem that has become much more complex by today.

 

Top shelves of first case.

 

Introduction to green land plants

What are the green land plants?

 

The green land plants are obviously green.  But unlike the related green algae, they have adaptations to live on land.  The most important of these are related to preventing drying out.  The first is an embryo protected by cells from the mother plant.  Second is a waxy coat covering the plant that is called a cuticle.  Third is a coat on the reproductive organ called a spore that allows it to survive on land until it germinates to make a new plant.  Later adaptations include water and food conducting (vascular) tissue, roots and leaves.   

 

There are five major groups of green land plants living today.  They are divided by whether they have vascular tissue, spores, seeds or flowers. 

  • BRYOPHYTES are small, nonvascular, spore-bearing plants that move food (sugar) and water by diffusion.  A common plant would be a moss a member of the Bryophytes. 
  • The vascular plants have specialized cells in tissues to conduct water (tracheids) and food (sieve cells).  Vascular plants include spore-bearing LYCOPODS (club moss) and FERNS (including equistetoids), as well as gymnosperms (such as pines) and angiosperm (flowering plants). 
  • Gymnosperms and Angiosperms are seed-bearing plants that have additional adaptations of the reproductive system: Seeds and pollen. These seed plants have spores that develop within the plant producing a seed with a baby plant (embryo) inside, and pollen grains with multiple cells. 
  • GYMNOSPERMS have seeds that are not enclosed by another organ. 
  • ANGIOSPERMS have seeds inside another organ, the fruit, that are found within a flower.  

 

The relationships between these five groups of plants have been determined by examining the characteristics of the plants as well as comparing the similarity of the DNA.  The resulting evolutionary tree fits well with the timing based on the fossil record.

For more about paleobotany, check out the UC Berkeley's on-line information. (The link takes you away from our web site.)

To see close-ups of the specimens in this display, Click Here.

Bottom shelves of first case

Other Parts of the Exhibit

Lobby Display Case (A 'Teaser' Case for Visitors)

The First Trees 

Seed Plant: Boldly Growing Where No Plant Has Grown Before 

Monster Plants That Created Coal  

Plants The Dinosaurs Ate 

Flowering Plants: The New Revolution

Updated February 9, 2015