Without question, bark is ponderosa pine's most outstanding characteristic. On young, vigorously growing trees, the bark is brown to black and deeply furrowed. These trees are often called "bull pines", or "blackjack" pines, and are so distinct in appearance that they are occasionally treated as a separate species. As trees mature, the bark develops large smooth plates split by deep furrows. These plates may be as long as four or five feet and as much as a foot and a half wide. It is in this phase that the bark develops the majestic orange-red color which so gracefully characterizes the ponderosa pine forests.