All living things seem to be in motion, and not just physically. They are constantly adapting and adjusting to suit their environment and thrive. It is not possible to grab an apple from a tree and assume that this is what all apples from all time have been like. There is a bit of mystery here, as the apple cannot adapt to the point of departing from "appleness" but it can also never be said that true "appleness" will ever be completely defined. This is because life is less about defining and more about exploration and wonder.
Like apples, coffee has a vast and ever evolving spectrum of varieties. Our favorite way to express this spectrum is as a series of relationships coffee has built with different terroir (growing regions) across the globe. All varieties are a function of this relationship series and all coffees we consume are built of one or more variety. It might be tempting to think that we could reach some sort of critical mass, when all varieties have materialized. The evidence against this is striking. We are constantly discovering new mutations. Some varieties that develop in one part of the world will be brought to another and develop even more character or mutate further. This seems to be an endless dance. Coffee farmers will often talk about how they become aware of the relationship between the earth and the plant by recognizing which varieties thrive and seem "happy." This intuitive realization will aid them in choosing what to plant on their farm. In a way, it's as if the soil and the selected variety are "pleased" to work together.
Where did coffee begin?
Coffee's ancient origins trace back to Ethiopia or Yemen, depending on who you ask. Modern coffee trees in the Ethiopian highlands are often referred to as 'Heirloom' or 'Indigenous' in order to express this provenance. Other varieties are named for where they were first observed, as production became global: Bourbon, Caturra, and Maragogype are examples. Some are named after those who discovered them like Pacas or Scott Labs (SL) 28. There are also hybrids that carry hybrid names like Pacamara (Pacas and Maragogype) or Maracatu (Maragogype and Caturra).
This is meant to be a primer on the concept of 'variety' and by no means a comprehensive list. The number of coffee varieties on earth is vast and probably not even completely known at this time. When buying your beans, the variety will contribute uniqueness but can also be overstated. In general, coffee trees that 'strain' more and produce less fruit will contribute more personality to the cup. This strain is often a function of variety, but terroir will also have a tremendous contribution. Something really exciting happens when both of these dimensions are maximized. Much can be made of and still discovered regarding the mystical interactions between dirt and DNA.
How can you explore coffee varieties?
Even though we do not simply consume coffee from the tree as we would an apple, the contributions of variety can often be equally exciting. It is not possible to truly separate the genetic component from all the others, but we still want to celebrate it and encourage its ongoing exploration. Your local roastery should have some single variety beans from time to time, and it is worth noting anything peculiar you find when tasting them. A few we recommend watching for are: Typica, Bourbon, Pacamara, Gesha (often poetically misnamed Geisha), SL 28, and of course Heirloom varieties from Ethiopia.
Note: Many use "varietal" to borrow from the vocabulary of wine. However in this case, "variety" is more botanically precise.