Say 'art' and most will think of painting or sculpture. There is a kind of sculpture, though, that takes as its raw material not stone or wood but a living tree. That is the art of bonsai.

From the Japanese word for 'tree in a tray', Bonsai is the art and product of shaping trees by careful pruning to produce a miniature tree or bush. Not produced from genetic dwarfs, bonsai are the result of years of patient shaping of ordinary species by master artists.

Because they are grown and shaped in a small pot, but are produced from ordinary species - pine, maple and many others - extreme care is required to keep the delicate plants healthy.

Soil type and temperature must be just so - conditions that are only within the artist's control within a certain range. Pruning techniques take years to master and are only possible to a certain kind of temperament. Potting and re-potting practices must be learned and they are many and varied.

Watering alone is a complex science for these small trees and bushes. Too much and the bonsai will become water-logged and develop fungi and root rot. Too little and the soil quickly becomes dry and leaves wilt and the tree dies.

Soil and potting practices overlap with watering needs since drainage is critical. Pruning habits interact with shaping techniques, which in turn are affected by soil maintenance and watering practices.

Bonsai are among the most difficult products of art to create as all these elements and many more have to be carried out to near perfection merely for the plant to survive. Add to that complexity the goal of creating pleasing shapes, styles and colors for both plant and pot and you have a high art.

On top of the inherent horticultural difficulty of learning and mastering a dozen sub-sciences, there is the need to master the artistic vision and skills to produce any of several basic or advanced styles.

There are five basic styles alone: formal upright, informal upright, slanting, cascade and semi-cascade. From that base branch out a dozen advanced types, including the literati and other difficult forms.

An art of that kind is not mastered in a month.

Craftsmen labor for years to produce a single tree, which may last a hundred years or longer. The trees are then often passed down from generation to generation, each successive artist adding his or her own distinctive style. As the tree is lovingly molded according to the personal aesthetic of each caretaker, past efforts are venerated and learned from.

Years of training and experience are required to become a skilled bonsai grower. Ordinary horticulture is by itself a difficult craft. But to produce a miniature tree from ordinary species takes a lifetime of patience and learning.

The results are widely regarded as well-worth the effort, though. Bonsai are admired the world over for their uniqueness, their longevity, variety and beauty and for the skill that goes to produce them.

In an age when brilliant technology can mass produce global cell phones and self-diagnosing automobiles, these individually designed and hand crafted, miniature works of art continue to inspire awe and admiration.