Blender use groups and joins. Think join is a permanent melting of 2 objects that become attached then they can be unattached but you have to that by hand with the vertices. Another way to do the same with out touching to much to the model objects compositions is to use groups, which joining objects but does not merge any vertices.
I found this topic necessary because when i attempting to export i selecting the hole object but they where not exporting. I was getting or the leaves or the bulk. Actually in the Outliner if you select both using shift it self work with out the need to use group. But if is a matter beyond the scope of exporting.