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Growing coffee

The number of species in the coffee genus has increased from 104 to 124 as a result of a new systematic study.

Coffea mannii
Coffea mannii, formerly the type species of the genus Psilanthus (Image O. Maurin)

The generic delimitation Coffea has troubled coffee researchers and taxonomists for more than 250 years. Only recently has molecular systematic research shown that, of the many genera previously associated with Coffea, only one genus, Psilanthus (20 species), is in fact closely related.

Indeed, some species of Psilanthus have previously been included in Coffea (Davis, 2010), as well as being used as local coffee substitutes and in trials for coffee production. Biological evidence from a variety of other sources also points to a close association between Coffea and Psilanthus, and it has been suggested on a number of occasions that they should be united into a single genus.

Coffea ambongensis

Coffea ambongensis with the fruit cut open to reveal brain-like coffee beans (Image A. Davis)


Psilanthus subsumed into Coffea

The argument has now been settled by research published in the Botanical Journal of the Linnean Society.

Kew scientists Aaron Davis, Nicolas Ruch and Mike Fay, together with James Tosh (Natural History Museum, London), investigated a broad range of Psilanthus and Coffea species in a molecular systematic study that used four plastid regions and one nuclear region in combination with morphological and other biological data. They concluded that Psilanthus should be subsumed into Coffea (Davis et al., 2011).

This decision means that the number of species in Coffea jumps from 104 to 124, and the natural distribution is extended from Africa and the Indian Ocean Islands to include tropical Asia and Australasia (Davis, 2011). The unique defining character of Coffea is the presence of coffee beans.

Item from Dr Aaron Davis (Rubiaceae Team Leader)
Kew Scientist, issue 41

Article references:

Davis, A. P. (2010). Six species of Psilanthus transferred to Coffea (Coffeeae, Rubiaceae). Phytotaxa 10: 41–45.

Davis, A. P., Tosh, J., Ruch, N. & Fay, M. F. (2011). Growing coffee: Psilanthus (Rubiaceae) subsumed on the basis of molecular and morphological data; implications for the size, morphology, distribution and evolutionary history of Coffea. Botanical Journal of the Linnean Society 167: 357–377.

Davis, A. P. (2011). Psilanthus mannii, the type species of Psilanthus, transferred to Coffea. Nordic Journal of Botany 29: 471–472.

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