Other than being classified together, they have little in common with each other.
The "D2-like" group of dopamine receptors are classified together based on structure but not drug sensitivity.
Especially in the slave states, all free people of color were classified together as black.
So also, forms which are not classified together may be superficially similar; for example, a young coastal plain and a peneplain.
These languages are sometimes classified together in the Zaza-Gorani language group.
Obviously tortoises and armadillos cannot be classified together in spite of their similarities.
Within the article class, comparable or "alike" products are classified together.
Such spheres are useful in clustering, where groups of similar data points are classified together.
Processes of the same nature that are classified together into a model.
Process models are processes of the same nature that are classified together into a model.