Coffee: the coffee plant is a shrub belonging to the Rubiaceae family, Coffea genus.
Several dozen species of the Coffea genus are known, but only two have an economic value: Coffea arabica and Coffea canephora, the only ones to be grown extensively by humans.
These plants account for nearly the whole of the world’s production, with the other two species cultivated, Coffea liberica and Coffea excelsa, playing a marginal role. Arabica is more widespread than robusta, representing about three quarters of the world’s production.
Although the roasted beans of the two species are very similar, the differences between the two plants and their seeds are significant, starting with genetic differences; arabica has 44 chromosomes while robusta only has half as many.
As its common name suggests, robusta is notably more resistant than the other species, both to attacks from parasites and diseases and to the heat: robusta plants can withstand several days in temperatures over 30°C, while arabica plants quickly become damaged in these temperatures.
More obvious differences between the two plants can be seen on the seeds: the arabica seed is flatter and longer and has a curvy groove on its flat side; it is a fairly vivid green in colour, sometimes with blue shading.
The robusta seed, on the other hand, is more convex and rounded, the groove is nearly straight and the green colour is usually pale with brownish or greyish shading. Chemically, the main differences are in the amounts of caffeine: 1.1 – 1.7 % for arabica and 2 – 4.5 % for robusta. The two species also look different in the cup; arabica is sweeter and more aromatic, noticeably less bitter and astringent.