Re: Which specimen (fossil) is most likely associated with coal deposits? WHY?

In general, plant fossils will be most commonly found in coal deposits.  
This is because coal is composed of plants that, through compression, 
heating, and some chemical changes, become coal over millions of years.  
However, there are no specific plants that are more commonly associated 
with coal than others because coal has formed over hundreds of millions of 
years in all parts of the world.

For more on coal formation, you can refer to most introductory textbooks on 
geology.  A particularly good textbook is Earth, by Press and Siever.  
Another good book that devotes a few pages to coal and its formation is 
Planet Earth by Emiliani (Cambridge University Press, 1992.