Is paper produced from different trees at all discernable?

As far as I know, no. Paper is mainly composed of cellulose, which is present in all trees. They use a complicated chemical process to make paper, which eliminates any structure that would make the different woods identifiable. The individual cells have been destroyed, along with any DNA, which is to fragile to survive the process. However, if you had enough scientific equipment, you could tell the difference between paper that was made different ways, due to chemical signatures. You might even be able to trace it back to a particular company, but only if that company’s paper is unique. So, no, paper is nearly impossible to trace to different places without additional information.

Actually the better paper is made from rag ( cotton ).
Some of the papers are a mix of rag, wood and other plant parts like flowers.
Some experts can tell when and with what ink type; where a book was made.

True about the cotton. Most paper currency for instance has some cotton in it. I don’t think paper for books would be easily distinguishable. I found this site which seems to have a lot of information, including links I have not explored but may answer your question more thoroughly.

You can tell a lot about paper fiber by looking at it through a loup. Paper is often a blend of recycled paper and new wood pulp. In addition to cotton and cotton blend, linen and flax can be added to paper. Based upon the composition of the paper, and expert probably can identify a manufacturer.

There are a lot of mills in Wisconsin, and if you’re in that area for any reason, detouring and taking a tour of a paper mill is worthwhile. There are also lots of specialty mills scattered throughout the country. You can also make paper at home, which is fun.

Not to the naked eye I wouldn’t think.