What is a phylogenetic tree and how to interpret it?

A phylogenetic tree is a diagram which represents evolutionary relationships among species. This method is used to determine the evolutionary relationship among taxonomic groups. It reflects how they evolved from common ancestors. If two organisms share a more recent common ancestor, they are more related.

Phylogenetic tree is required for UniFrac distance (weighted or unweighted) based analysis, such as beta diversity analysis.

More details on generating phylogenetic trees can be found here