All coffee comes from plants of the genus Coffea, which is comprised of 10 species, only two of which are of relative importance. The first, Coffea Canephora, or Coffea Robusta, comprises only a small portion of the worlds coffee supply, with estimates ranging from 10 - 30%. Robusta trees are resilient, adaptive, and high yielding. The species typically produces beans of inferior quality, best suited for use in instant coffee, or commercial blends striving for economy. High quality Robusta does exist, however, and is valued by some as a component in an espresso blend, where it can produce visually impressive crema and assert its flavor in large amounts of milk.
The second species, and the one most valued by today's specialty coffee industry, is Coffea Arabica. Coffea Arabica produces all of the worlds best coffee. It is less productive, more disease susceptible, and generally more difficult to grow than its sibling, but rewards the careful farmer with a higher quality crop, shining with the distinct, delicious flavors coffee lovers desire.
Within the species, there are many botanical varieties each with their own unique characteristics. Many, like Bourbon and Gesha, have been around for well over a hundred years. Others, like Catimor and Ruiru 11, are the intentional result of breeding programs aimed at producing hardier or higher yielding plants. These hybrids often contain a portion of other species in their pedigree, but are, for all practical purposes, considered Arabica. Botanical varieties vary in many aspects, and cup quality is no exception. The lower yielding heirloom strains usually produce the superior cup.