In systematic four types of relationships are studied and they are:
a) Relationships of phylogeny (evolutionary descent) or the degree to which two organisms are thought to be related to a common ancestor.
b) Relationships of similarity in morphology (appearance and structure) physiology, cytology etc.
c) Spatial or geographical relationships
d) Trophic or nutritimal relationships, which study the extent to which two or more organisms depend upon each other or compete with each other for food.