Ah, you don't understand how the Unix shell and globs (a.k.a. wildcards work).
Suggestion: Find a book that explains Unix basics. No, I don't know what book that would be.
Here is a nutshell explanation, perhaps hard to understand, and highly incomplete. Wildcard expansion is done by the shell, before calling the program. Say in my current directory /home/ralphbsz/, I have 3 things: a subdirectory ax/, a file ay.txt, and a python source file az.py. If I say "ls", the shell starts the ls executable (which is a program), which lacking any particular input will show a listing of files in the current directory. If I say "ls ay.txt", the shell will start the ls program with argument ay.txt, and ls will show a listing (perhaps with details) of file ay.txt. If I say "ls *.py", the shell will expand that by searching THE CURRENT DIRECTORY for all files that match *.py, and it will run the ls program with argument az.py, which will show me exactly that one file.
Where it gets interesting: If I say "ls a*", the shell will translate that into "ls ax ay.txt az.py". The ls program will show me all the content of directory ax, plus the two files ay.txt and az.py. So for example if the directory ax/ contains files ax/1.foo and ax/2.bar, the output will be something like "ax/1.foo ax/2.bar ay.txt az.py" (in reality, ls formats the output a little more nicely, but you get the basic idea).
OK, so what would happen in my example if I do "ls *.txt"? I would get ax.txt. What if I do "ls *.foo"? It would output NOTHING, because the glob expansion of *.foo just doesn't work, so the ls program would be told to please give details of the file *.foo, which does not exist. (Footnote: A file name *.foo might exist, it is not illegal to create files whose names contain * or ?, but it is also a very bad idea, unless you want to confuse beginners).
All the "-R" in the world doesn't help you here: The shell takes the command line "ls *.foo" and tries to expand it right here, and that does not give the result you want.
There are many ways to get what you want. The most common one (I think?) would be to not use the -R option on ls, but instead to use the command that's designed for this usage: "find . -name \*.foo" (yes, there is a backslash in front of the * which I will explain in a moment). The find command automatically recurses from all starting point you listed, so it will read all files and directories in *. It then can do wildcard (glob) expansion and checking internally, so if it finds any files whose names match the pattern *.foo, it will print their name. Why the backslash? To protect the * character from shell wildcard expansion: If the current directory contained a file named blatz.foo, the shell would expand the above command line to "find . -name blatz.foo", which is not what you want.
Hope this helps. It takes a while to internalize this, but is vitally important knowledge.
P.S. Personally, I think the fact that the shell auto-expands globs, and that called programs can not even go back to the shell and ask "what did the user really type" is a giant misfeature of Unix. It was a quick hack which allowed two overworked computer science researchers (Dennis and Ken) to get their quick hack operating system running faster, without having to implement globbing in all the called programs, or in a shareable library. If Unix had been designed by real software engineers (like VMS or VM or MVS or RSX-11 or Primos or ... were), instead of computer science researchers, this would have been handled sensibly. Alas, Unix was not intended to be a production environment that is user friendly, but it was intended as a research tool. Rant off.
