I have got quite unusual maple trunk. I dig it in autumn 2013 - check this post
. I have never ever seen a bonsai with such bumped trunk. This bumps, or knots, are probably tumors, which can be caused by mechanical damage, insect, or fungal and bacteria disease. Well, no bonsai like this, but never mind, I´m going to have one :). I saw many trees, or let´s say the whole forest with bumps, on my walks in Carpatian mountains. Trees with this strange knots in this forest were mostly acacias (Robinia pseudoacacia),
and Prunus species.
My tree is circa 65-70 cm tall, and has nice old character knots and
natural uro in upper part of the trunk. It grew in swampy area near the
river Danube, not in this strange Carpatian forest. I transplanted it in smaller
plastic container a week ago and used guide wires for some branches...