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The trees which produce coffee are in the genus Coffea
which belongs to the Rubiaceae family. There are about
50 different species although only two of these are
commercially significant, Coffee arabica and Coffee
canephora, which is usually referred to as robusta.
Coffeea arabica grows on steep slopes and plateaux
at altitudes of between 600 and 2000 metres while robusta
grows well in the humid, tropical climate of the equatorial
forests in altitudes from sea level to 600 metres.
Arabica accounts for about 75% of world production.
 A
further botanical characteristic of coffee is that sometimes
the blossom, green, yellow and ripe red cherries appear
together on the same branch which make it difficult
to harvest any other way than by hand.
There are a few visible botanical features to distinguish
the two commercial species of coffee tree, although
robusta has larger leaves which have a more corrugated
appearance than arabica. Robusta is also more resistant
to diseases.
The berries gradually change from dark green to yellow
as they ripen and after several months they become deep
red cherries. These cherries are about 1.5cm in length;
arabica cherries are oblong while those of robusta are
rounded.
Red skin covers a sweet pulp which usually contains
two coffee seeds shaped rather like two half beans.
These beans, each covered by a thin delicate layer called
"silver skin", are encased in a this brittle
husk called "parchment".
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