Wood is identified using the features and tools that are appropriate to the size of the sample. Large timbers are identified by looking at the color, the appearance of the end and side grain, whether a saw cuts cleanly or leaves lots of splinters behind, whether the wood has straight or curly drying cracks, and so forth. The hardness and density provide valuable information as well. For smaller pieces of wood, it’s more practical to look directly at the wood cells with a 10X hand lens (also called a loupe). Different species have different characteristics and combinations of these features are used to identify the sample using a key.
Conners, Terry, "Introduction to Wood Structure and Characteristics" (2015). Agriculture and Natural Resources Publications. Paper 104.