Penjing is where bonsai has it’s roots from. It is a landscape of rocks and trees instead of a single tree as the standard bonsai form. Put simply, it’s a landscape in miniature.
Penjing is very important to bonsai because bonsai is actually a refined version of the art. When we add rocks, models and accent plants to our pots we are actually crossing the boundary into another art form called penjing. Sometimes we cross into this art by accident in bonsai. I am not too sure about this, but it seems the Chinese call bonsai penjing as well as the penjing that we know. Over at Mai Lung Penjing they give a great explanation of how to create penjing and also a good example of junipers in the style on this page. It seems a good site to learn all about the art.
At the Chinese gardens of Yangzhou this have some very dramatic examples of penjing.