How do plants make caffeine?

Caffeine occurs naturally in a number of plants. The most well-known of these are tea, coffee, and the cocoa plant. Coffee and tea contain more caffeine than the cocoa plant, which just contains small amounts.

There are other plants, however, which naturally contain caffeine. These include yerba mate, guayusa, and yaupon, which are all species of holly. A few other species of holly also contain some caffeine. Another unrelated plant (related to maple trees actually), called guarana, contains caffeine.

There may be others but these are the only plants that I know of that contain caffeine.