Csaba Pozsárkó at has created a tutorial on face-me billboard (or 2D) tree components.  He walks you through the steps of turning a tree image into a component.  Even though the tree is a stood up flat image, SketchUp has a setting in the Make Component dialog box that lets one have the tree always face the viewer no matter where you are looking at the model.  It gives the illusion of the tree being fully 3D without the larger amount of geometry (and bigger file size) that would slow down your computer.


He also demonstrates how to cut out the rectangular background so that the component will cast a better shadow.  This can be done by hand by running a drawing tool around the image or one can use two plugins mentioned: Image Profile or Image Trimmer.


All this is useful to grow your own plant library based on images of your choosing for your locale.