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The Coffee Plant

Coffee belongs to the botanical family Rubiaceae, which has some 500 genera and over 6,000 species. Most are tropical trees and shrubs which grow in the lower parts of forests. Other members of the family include the gardenias and plants which yield quinine and other useful substances, but Coffea is by far the most important member of the family economically.

Since the genus Coffea was first correctly described by Linnaeus in the mid 18th century, botanists have failed to agree on a precise classification system. There are probably at least 25 major species, all indigenous to tropical Africa and certain islands in the Indian Ocean, notably Madagascar. Difficulties in classification and even in designation of a plant as a true member of the Coffea genus arise because of the great variation in the plants and seeds. All species of Coffea are woody, but they range from small shrubs to large trees over 10 metres tall; the leaves can be yellowish, dark green, bronze or tinged with purple.

The two most important species of coffee economically are Coffea arabica (Arabica coffee) - which accounts for over 70% of world production - and Coffea canephora (Robusta coffee). One other species which is grown on a much smaller scale is Coffea liberica (Liberica coffee).

Old names and synonyms:

C. bukobensis and C. robusta (both now C. canephora), C. arnoldiana, C. aruwimiensis, C. dewevrei, C. dybowskii and C. excelsa (all now C. liberica)

Some differences between Arabica and Robusta coffee :

Coffea arabica - Arabica coffee

Coffea arabica was first described by Linnaeus in 1753. The best known varieties are 'Typica' and 'Bourbon' but from these many different strains and cultivars have been developed, such as caturra (Brazil, Colombia), Mundo Novo (Brazil), Tico (Central America), the dwarf San Ramon and the Jamaican Blue Mountain. The average arabica plant is a large bush with dark-green oval leaves. It is genetically different from other coffee species, having four sets of chromosomes rather than two. The fruits are oval and mature in 7 to 9 months; they usually contain two flat seeds (the coffee beans) - when only one bean develops it is called a peaberry. Arabica coffee is often susceptible to attack by pests and diseases, therefore resistance is a major goal of plant breeding programmes. Arabica coffee is grown throughout Latin America, in Central and East Africa, in India and to some extent in Indonesia.

C. arabica from old manuscript. (Source)

Coffea canephora - Robusta coffee

The term 'robusta' is actually the name of a widely grown variety of this species. It is a robust shrub or small tree growing up to 10 metres in height, but with a shallow root system. The fruits are rounded and take up to 11 months to mature; the seeds are oval in shape and smaller than those of C. arabica. Robusta coffee is grown in West and Central Africa, throughout South-East Asia and to some extent in Brazil, where it is known as Conillon.

C. robusta berries or cherries (Source)

Coffea liberica - Liberica coffee

Liberica coffee grows as a large strong tree, up to 18 metres in height, with large leathery leaves. The fruits and seeds (beans) are also large. Liberica coffee is grown in Malaysia and in West Africa, but only very small quantities are traded as demand for its flavour characteristics is low.

C. liberica trees (Source)

Arabica / robusta hybrids

Crosses between arabica and robusta aim to improve arabica by confering disease resistance and vigour or to improve on the cup quality of robusta. The flavour characteristics can be either more like arabica, or more like robusta, depending on the variety.

References :

• http://www.ico.org
• http://www.plantna.com