About 60 percent of the world’s coffee comes from Coffea arabica, yet in the wild it is classified as endangered, surviving in shrinking mountain forests of South Ethiopia, South Sudan, and Yemen. Arabica arose between roughly 543,000 and over a million years ago when Coffea canephora, known as Robusta, crossed with Coffea eugenioides in East Africa. Instead of a sterile offspring, the new plant became an allotetraploid, keeping both parents’ full genomes for 44 chromosomes. It demands altitudes around 1,200 to 1,500 meters, temperatures of 15 to 24 degrees Celsius, steady rain, and shade.

Nearly all cultivated Arabica descends from a handful of plants taken out of Yemen through the port of Mocha, so plantations hold less than 1 percent of the genetic diversity of the wild Ethiopian forests. Those forests once covered about 31 percent of Ethiopia and now cover about 4 percent. Warming lets the coffee berry borer climb to higher farms, and leaf rust cut Central American output by 16 percent in 2012 and 2013 and costs up to $2 billion a year. Models suggest over half of today’s coffee land could be unsuitable for Arabica by 2050, and since 2023 some big roasters have quietly dropped 100% Arabica from their bags.

• A string of sunny days can make a tree overflower and drain its own roots and leaves to feed the fruit.
• Outside its native range, Arabica spreads as an invasive weed in Hawaii, Sri Lanka, and Queensland.
• Wild populations in Ethiopia could fall by up to 80 percent by 2088 from climate stress.
• Coffea stenophylla from West Africa tastes close to good Arabica but tolerates far more heat.
• Natural mutants labeled AC1, AC2, and AC3 contain about 0.76 milligrams of caffeine per gram versus about 12 for normal Arabica.