leafs with particle billboards

Ik have three questions about making leafs:

  1. I have made a jpeg with a black and white shape of a leaf and applied it to some particle billboards. Why does my render only show part of my leaf shape on each billboard?
  2. Why does blender make those ugly edges around the leafs?
  3. how do i make the leafs stand up from the basic sphere in stead of lying on the sphere?

Hope you can help.