The pits in the drupe (a fruit like a cherry or peach) are the coffee beans of commerce. How might the caffeine in the seeds (which pleasantly stimulates the human nervous system) better adapt them for survival? Excess caffeine can cause dizziness, anxiety, mild delirium and heart palpitations. Native to tropical Africa, the species is cultivated in tropical areas worldwide- providing a nice example of the common pattern in the biogeography of cultivated plants, where a species is often a more economically important crop outside its native range. Coffee is often grown as an understory shrub beneath trees, an agricultural system that mimics the commonest ecological role of members of the family as a whole- understory shrubs in tropical rainforests. In patches of Madagascar forest, wild varieties of coffee have been found which are caffeine-free.