The Coffee plant is botanically a shrub.  Part of the Rubiaceae family.  Only 3 of the 73 classified species are used for Coffee production.  They are Arabica, Robusta and  Liberica.   Each provides different yields but typically will yield 3-12 tons per hectare.

Coffee production is VERY similar to wine production and the application of Terroir is just as key in Coffee as it is in wine.

Arabica.

Arabica (Coffee arabica) was the original plant used for today's coffee production.  Thought to originate from present day Ethiopia.  This variety contains less caffeine than its relatives but typically has the best flavor.

Arabica trees grow between 12 and 20 feet.  Most of the harvesting is done by hand as it grows in high mountainous land making large mechanical harvesting equipment hard to operate.  There are 2 main varieties of Arabica - Bourbon and Typica.  There are also sub-varieties (taken from the original two) and these are known as 'Cultivars'.  Bourbon requires significant space and care, yields more than Typica (about 1/4 to 1/3) and grows at 3000-6500+ feet) but produces the highest quality coffee.  Typica (original type) produces lower yields but is less 'fussy'.  Other verities include, Blue Mountain, Catimor, Catuai, Maragogype, Pache Commum, Timor.

Robusta

Coffea canephora.  Typically a higher concentration of Caffeine and more "hardy" than traditional Arabicas.  Robusta trees are shorter than arabica (making them easier to pick) and cna be growen more compactly.  Common opinion is though that the flavor is not as good as arabica.  

Liberica.

As leaf rust ran rampant in the late 19th century author Francis Thurber predicted that the Liberica would replace Arabica - it hasn't yet with little penetration in the mature Coffee markets of the US and Europe.  With yields lower than Robusta and flavor lower than Arabica Liberica hasn't taken off as much, yet.  Coffea liberica.