Coffee beans are the seeds of coffee trees (genus Coffea). There are over two dozen varieties, but the most common are Coffea arabica, simply known by consumers as "arabica" and the lesser known Coffea canephora, known as robusta.  Coffea arabica is usually grown at higher altitudes, and compared to robusta, has less caffeine, superior taste characteristics and garners a higher price on the coffee market.  Arabica accounts for about 75% of the world's coffee production and usage.  The coffee tree is really a large bush which can grow to 15 feet in height, but is usually pruned to make picking its fruit easier.  First-fruits appear after about four years and continue to do so seasonally for 20-30 years. Each fruit, known as a coffee cherry, usually contains two seeds (fruits containing only one seed are known as "peaberries") and turns a glossy, deep red when fully ripe.  About 12-20 kg of coffee beans result from each 100 kg of harvested fruit.  The fruit pulp itself has no commercial value.