Most of the greens that are used in floral arrangements are Salal branches, Leather fern (found frequently on sides of the road in northern Ontario i.e. Kirkland lake, Timmins, Kapuskasing, etc.), pittosporum, asparagus fern, and aspidistra leaves. Depending on the florist the types of greens they usually carry varies. These greens are used to keep the flowers balanced and to make the arrangement look fuller. Greens can also be used in a sparse amount to create a modern look and give the arrangement a clean lined sophistication.
All greens can be manipulated to create a different look when designing. They can be used to give a dramatic height, to cover your oasis/ mechanics, to create a line, or to be just really cool looking. For example the picture below is an arrangement I did at a work shop, we got steel grass (the triangles sticking out on top of the arrangement), aspidistra leaves that are curled up and pinned to keep their shape. Those however are the only greens even though the Hypericum berry (considered a flower) and the green hydrangea are also incorporated in the design.