"How can they say that one species belongs here and another doesn't?"

It is one of about 2000 total species belonging to this family.

It is only one of the 800 total species belonging to this family.

Fish Base considers this species to belong to its own family.

Well over 166 species belonging to about 16 different orders and 47 families have been recorded here.

But what taxonomic groups do these two species belong to?

The new species belongs to a group of plants which are known for their bizarre flowers.

Most species belong to just a few of its 11 phyla.

What species belong to it has been highly contentious for many decades.

These species too soon crowd out the desirable ones and do not belong in a meadow.