The Coffee Plant

The Genus Coffea

Coffea is a genus of flowering plants in the family Rubiaceae (the madder family), comprising shrubs and small trees native to tropical and southern Africa and tropical Asia. The genus and its type species, Coffea arabica, were first formally described by Carl Linnaeus in 1753. Since then, botanical exploration has steadily expanded its boundaries: as of early 2026, Plants of the World Online recognises 133 accepted species and one hybrid.

The genus is still growing. In 2008 and 2009, researchers from the Royal Botanic Gardens, Kew, named seven new species from the mountains of northern Madagascar alone. That same year, two species were identified in Cameroon — including Coffea charrieriana, which is notably caffeine-free — opening theoretical doors to naturally decaffeinated breeding lines. In 2011, the twenty species of the former genus Psilanthus were absorbed into Coffea on the basis of overwhelming morphological and genetic similarity, extending the genus's native distribution to tropical Asia and Australasia.

A landmark coffee genome publication in 2014 identified more than 25,000 genes and revealed that coffee plants evolved the capacity to synthesise caffeine using a different set of genes from those found in tea (Camellia) or cacao (Theobroma) — a striking example of convergent evolution. A comprehensive phylogeny published in 2017 suggested Africa or Asia as the likely ancestral origin of the genus, with several independent radiations across Africa, Asia, and the Western Indian Ocean Islands.

Despite this diversity, global commerce depends overwhelmingly on just two species, and a third holds regional and emerging significance.

Two Dominant Species — and One Rising Third

The coffee trade is built almost entirely on a narrow genetic base. Coffea arabica and Coffea canephora together account for virtually all commercially produced coffee, with Coffea liberica constituting a small but culturally and agronomically notable remainder.

Coffea arabica — Arabica

Coffea arabica is widely regarded as the first cultivated coffee species and remains dominant, accounting for approximately 55–60% of global production depending on the source. Its natural populations are restricted to the montane forests of south-western Ethiopia, South Sudan, and Yemen.

Genetically, Arabica is unusual within the genus: it is an allotetraploid, carrying four copies of eleven chromosomes (44 total), arising from a ancient hybridisation between the diploids C. canephora and C. eugenioides. This hybridisation event is estimated to have occurred between roughly 543,000 and 1.08 million years ago, linked to shifting environmental conditions in East Africa.

In cultivation, Arabica thrives at altitudes commonly between 1,200 and 1,500 m, though plantations exist from sea level to as high as 2,800 m. It performs best at average temperatures of 15–24 °C and annual rainfall of approximately 1.2–1.8 metres, evenly distributed. It prefers light shade and well-drained soils. The plant takes approximately seven years to mature fully, producing small white, highly fragrant flowers three to four years after planting.

From a sensory standpoint, Arabica beans are associated with sweeter taste, higher acidity, and a richer, more complex flavour profile compared to Robusta, partly because the plant contains more sugar (around 6–9%) and somewhat lower caffeine (approximately 0.8–1.4%).

Coffea canephora — Robusta

Coffea canephora, commercially known as Robusta, originates in central and western sub-Saharan Africa, growing indigenously from Liberia across to Tanzania and south to Angola. It was not formally recognised as a distinct species until 1897 — more than a century after Arabica's description.

Robusta accounts for roughly 45% of global production. Its cultivation is concentrated in Vietnam (where French colonists introduced it in the late 19th century), as well as Uganda, Indonesia, India, and Brazil — where the conilon variety is widely grown.

The plant is physiologically and agronomically distinct from Arabica in several important ways:

• It grows as a robust shrub or tree to around 10 metres, with a shallow root system.
• It is significantly more resistant to pests and disease and requires less herbicide and pesticide.
• It contains markedly more caffeine — approximately 2.7% versus Arabica's 1.5% — and less sugar (3–7% versus 6–9%).
• It tolerates warmer conditions, performing well at 24–30 °C, at lower altitudes than Arabica.
• Berries take approximately 10–11 months to ripen.

In the cup, Robusta produces a strong, full-bodied brew with pronounced bitterness and earthy, woody flavours, distinct from Arabica's fruitier character. While often used as a filler in lower-grade blends, high-quality Robusta is valued in Italian espresso culture for contributing body and crema, and growing interest from specialty roasters has begun to reframe the species's reputation.

Coffea liberica — Liberica

Coffea liberica is the most commercially significant of the remaining species, noted as a lesser-known species grown for consumption alongside C. racemosa. Native to West and Central Africa, it is cultivated primarily in parts of the Philippines, Malaysia, and West Africa, where it holds cultural importance. Its large beans and distinctly bold, sometimes smoky or floral flavour profile set it apart from both Arabica and Robusta. Though it represents a small fraction of global trade, Liberica is increasingly discussed in the context of climate resilience, given its tolerance of conditions where Arabica struggles.

For a detailed comparison of all three species, see Coffee Species: Arabica, Robusta & Liberica.

Varieties, Cultivars, and the Meaning of Genetic Diversity

Below the species level lies an intricate world of varieties and cultivars that has enormous implications for flavour, disease resistance, and agricultural viability. Within Coffea arabica alone, hundreds of named varieties exist — from traditional heirloom landrace populations in Ethiopia, to long-established varieties such as Typica and Bourbon that spread from Yemen across the globe, to modern F1 hybrid cultivars developed through formal breeding programmes.

The concept of a cultivar (cultivated variety) matters because genetic differences between plants — even within a single species — can produce meaningfully different cup profiles, yield levels, and responses to environmental stressors. The narrow genetic base of cultivated Arabica, itself a product of a single ancient hybridisation, makes diversity within the species both precious and fragile.

DNA fingerprinting techniques, proven effective for coffee in a 2020 study using SSR marker analysis, are beginning to enable greater traceability and transparency across the supply chain, as well as improved guidance for farmers on their plants' susceptibility to pests and disease.

For a full treatment of named varieties, their lineages, and cup characteristics, see Coffee Varieties & Cultivars. For the science of breeding and genomics, see Coffee Genetics & Breeding.

The Fruit: Anatomy of a Coffee Cherry

Coffee is the seed of a fruit — a point that anchors much of its flavour science. The coffee cherry (botanically, an epigynous berry or indehiscent drupe, depending on species) ripens to red or purple and typically encloses two seeds positioned flat-side together. These seeds are the "beans." In approximately 5–10% of fruits, only one seed develops, forming a smaller, rounded peaberry.

The cherry's layers — from outer skin (exocarp) through the mucilaginous pulp to the inner parchment and silver skin — all interact with the seed during post-harvest processing, influencing the final flavour of the green bean. The fruit and leaves also contain caffeine and have historically been used to prepare beverages such as coffee cherry tea (qishr) and coffee-leaf tea.

The Ecology of Caffeine

Caffeine is not merely a human stimulant — for the coffee plant, it serves a dual ecological function. It acts as a natural pesticide, providing some defence against insects and other herbivores. Simultaneously, it functions as a pollinator attractant: caffeine creates an olfactory memory in honeybees that encourages them to return to the plant's flowers.

Not all Coffea species contain caffeine. Caffeine appears to have evolved independently in multiple lineages within the genus, possibly in response to high pest pressure in the humid environments of West-Central Africa. The parallel independent evolution of caffeine biosynthesis in coffee, cacao, and tea — via different gene sets — is one of the more remarkable examples of convergent molecular evolution in the plant kingdom.

Insect pests that affect coffee production include the coffee borer beetle (Hypothenemus hampei) and the coffee leafminer (Leucoptera caffeina), both of which represent significant agricultural threats.

Growing Conditions and Their Effect on the Cup

Genotype sets the ceiling of a coffee's potential; terroir — the sum of altitude, climate, soil, and shade — determines how much of that potential is realised. The two commercially dominant species illustrate this clearly: Arabica's preference for high-altitude, cooler temperatures and consistent moderate rainfall gives its beans more time to develop complex sugars and aromatic precursors, which translates to the flavour complexity associated with specialty coffee. Robusta's adaptation to lower altitudes and higher temperatures is part of what shapes its bolder, more bitter character.

Coffee plants grow within the Bean Belt — the band of tropical regions between the Tropics of Cancer and Capricorn. Within this zone, variables such as volcanic soil composition, cloud cover providing natural shade, diurnal temperature variation, and rainfall patterns all interact with plant genetics to shape acidity, body, and aromatic compounds in the green bean.

Both C. arabica and C. canephora are vulnerable to climate change-driven shifts in their viable growing zones, which researchers project will reduce production in some of the world's most important growing regions. This makes the development of new varieties, hybrids, and the exploration of resilient wild Coffea species increasingly urgent priorities.

For a detailed guide to how growing conditions shape coffee quality, see Growing Coffee: Altitude, Shade & Soil.