Nearly all the world’s coffee comes from two species: Coffea arabica, prized for flavor but dependent on cool highlands, and Coffea canephora, or Robusta, hardier but harsher. Coffea stenophylla, the narrow leaved coffee also known as highland or Sierra Leone coffee, grows as a shrub or small tree of 3 to 6 meters across Guinea, Ivory Coast, Liberia, and Sierra Leone, with glossy tapered leaves and berries that ripen dark purple to nearly black. Swedish botanist Adam Afzelius found it in the 18th century, and Scottish botanist George Don formally described it in 1834.

In 1894 Sir William H. Quayle Jones, deputy governor of Sierra Leone, sent seeds to Kew, and plants reached Trinidad, where superintendent J. H. Hart reported in 1898 that the coffee was excellent and equal to the finest arabica. Its small berries and low yields made it unprofitable for a bulk commodity trade, and it dropped out of cultivation. With leaf rust spreading and highland farms warming, Kew’s head of coffee research Aaron Davis and colleagues went looking for it, found wild plants in Ivory Coast and Sierra Leone in 2019 and 2020, and saw it perform well at around 150 meters of elevation.

• Blind tastings describe it as naturally sweet with medium high acidity, fruitiness, and good mouthfeel.
• Arabica usually needs 800 meters or more; in low, hot places its fruit ripens too fast and tastes flat.
• By 2018 researchers found stenophylla was not commercially grown anywhere on Earth.
• It is listed as Vulnerable on the IUCN Red List, threatened by deforestation in the Upper Guinean forests.
• It could be grown as a crop in its own right or crossed with commercial coffee to add heat tolerance.