A brownian tree is a form of computer art that was briefly popular in the 1990s, when home computers started to have sufficient power to simulate brownian motion. Brownian trees are mathematical models of dendritic structures associated with the physical process known as diffusion-limited aggregation.
A brownian tree is built with these steps: first, a "seed" is placed somewhere on the screen. Then, a particle is placed in a random position of the screen, and moved randomly until it bumps against the seed. The particle is left there, and another particle is placed in a random position and moved, and so on.
The resulting tree can have many different shapes, depending on principally three factors:
At the time of their popularity (helped by a Scientific American article in the Amateur Scientist section), a common computer took hours, and even days, to generate a small tree. Today's (2003) computers can generate trees with 10,000's of particles in a few minutes.