I get asked quite frequently to identify a wood or a tree, sometimes I'm given an actual wood sample, but sometimes I get incredibly vague descriptions like "it came from a tree that was big and old, do you know what it was?" Yes, that's an actual quote from personal experience!
Identifying a wood sample can be challenging, and I'm pretty decent at wood ID, so I wanted to share some resources I use to help out.
First, I use The Wood Database: http://www.wood-database.com/ Its a comprehensive data catalog on most wood varieties you'll ever be able to get your hands on and can give you a good look at the differentiation characteristics of species. I've found the photos sometimes are not very representative, but they do give you a good idea. Woods have many colloquial names, and the database helps sort through some of that confusion as well.
I also keep on hand a copy of Wood, Identification and Use for something a bit more tactile, I've linked to the hardcover on Amazon below.
Some features that set species apart can't be seen by the eye, such as open or closed cell structure, so an inexpensive jeweler's loupe is handy. the one I use is 10x magnification:
Nothing can substitute for getting your hands on a sample of wood of known specie, and don't just take someone's word for it! I've known foresters who couldn't identify cherry to save their life! Remember that a species of wood can look totally different depending on the direction of cut, from heartwood to sapwood, and region to region, so look at multiple samples if you can!
The more wood you get your hands and eyes on, the better you'll get at identification, if you're struggling, shoot me an email at firstname.lastname@example.org and I'll try to help out!
Here are a few more resources and links via amazon:
The Wood Bible: http://amzn.to/2z9ISPn an additional ID book
Identifying Wood: http://amzn.to/2z9RF3S Out of date, but solid technical guide for most woods you would use.
Wood ID Kit: http://amzn.to/2zbF93Y A set of actual veneer wood samples of some common woods for you to physically reference.