Coffea is a genus of flowering plants in the family Rubiaceae. Coffea species are shrubs or small trees native to tropical and southern Africa and tropical Asia. The seeds of some species, called coffee beans, are used to flavor various beverages and products. The fruits, like the seeds, contain a large amount of caffeine, and have a distinct sweet taste.

The plant ranks as one of the world's most valuable and widely traded commodity crops and is an important export product of several countries, including those in Central and South America, the Caribbean and Africa. The coffee trade relies heavily on two of the over 120 species, Coffea arabica (commonly known simply as "Arabica"), which accounts for 60–80% of the world's coffee production, and Coffea canephora (known as "Robusta"), which accounts for about 20–40%.

Both coffee species are vulnerable to shifts, caused by climate change, in their growing zones, which are likely to result in a decline in production in some of the most important growing regions.

There are over 130 species of Coffea, which is grown from seed. The two most popular are Coffea arabica (commonly known simply as "Arabica"), which accounts for 60–80% of the world's coffee production, and Coffea canephora (known as "Robusta"), which accounts for about 20–40%. C. arabica is preferred for its sweeter taste, while C. canephora has a higher caffeine content. C. arabica has its origins in the highlands of Ethiopia and the Boma Plateau of Sudan, and came about as the result of a hybrid between C. canephora and C. eugenioides.

The trees produce edible red or purple fruits that are either epigynous berries or indehiscent drupes. The fruit is often referred to as a "coffee cherry", and it contains two seeds, called "coffee beans". Despite these terms, coffee is neither a true cherry (the fruit of certain species in the genus Prunus) nor a true bean (seeds from plants in the family Fabaceae).

In any coffee crop, about 5–10% of fruits contain only a single bean. Called a peaberry, it is smaller and rounder than a normal coffee bean.

When grown in the tropics, coffee is a vigorous bush or small tree that usually grows to a height of 3–3.5 m (9.8–11.5 ft). Most commonly cultivated coffee species grow best at high elevations, but do not tolerate freezing temperatures.

The Coffea arabica tree grows fruit after three to five years, producing for an average of 50 to 60 years, though up to 100 years is possible. The white flowers are highly scented. The fruit takes about nine months to ripen.

The caffeine in coffee beans serves as a toxic substance that protects against insects and other pests, a form of natural plant defense against herbivory. Caffeine simultaneously attracts pollinators, specifically honeybees, by creating an olfactory memory that signals bees to return to the plant's flowers. Not all Coffea species contain caffeine, and the earliest species had little or no caffeine content. Caffeine has evolved independently in multiple lineages of Coffea in Africa, perhaps in response to high pest predation in the humid environments of West-Central Africa.

Caffeine has also evolved independently in the more distantly related genera Theobroma (cacao) and Camellia (tea). This suggests that caffeine production is an adaptive trait in coffee and plant evolution. The fruit and leaves also contain caffeine, and can be used to make coffee cherry tea and coffee-leaf tea. The fruit is also used in many brands of soft drink as well as pre-packaged teas.

Several insect pests affect coffee production, including the coffee borer beetle (Hypothenemus hampei) and the coffee leafminer (Leucoptera caffeina).

Coffee is used as a food plant by the larvae of some Lepidoptera (butterfly and moth) species, Dalcera abrasa, turnip moth and some members of the genus Endoclita, including E. damor and E. malabaricus.

New species of Coffea are still being identified in the 2000s. In 2008 and 2009, researchers from the Royal Botanic Gardens, Kew, named seven from the mountains of northern Madagascar, including C. ambongensis, C. boinensis, C. labatii, C. pterocarpa, C. bissetiae, and C. namorokensis.

In 2008, two new species were discovered in Cameroon: Coffea charrieriana, which is caffeine-free, and Coffea anthonyi. By crossing the new species with other known coffees, two new features might be introduced to cultivated coffee plants: beans without caffeine and self-pollination.

In 2011, Coffea absorbed the twenty species of the former genus Psilanthus due to the morphological and genetic similarities between the two genera. Historically, the two have been considered distinct genera due to differences in the length of the corolla tube and the anther arrangement: Coffea with a short corolla tube and exserted style and anthers; Psilanthus with a long corolla tube and included anthers. However, these characteristics were not present in all species of either respective genus, making the two genera overwhelmingly similar in both morphology and genetic sequence. This transfer expanded Coffea from 104 species to 124, and extended its native distribution to tropical Asia and Australasia.

The coffee genome was published in 2014, with more than 25,000 genes identified. This revealed that coffee plants make caffeine using a different set of genes from those found in tea, cacao and other such plants.

A robust and almost fully resolved phylogeny of the entire genus was published in 2017. In addition to resolving the relationships of Coffea species, this study's results suggest Africa or Asia as the likely ancestral origin of Coffea and point to several independent radiations across Africa, Asia, and the Western Indian Ocean Islands.

In 2020, a technique of DNA fingerprinting, or genetic authentication of plant material, was proven effective for coffee. For the study, scientists used DNA extraction and SSR marker analysis. This technique or similar ones may allow for several improvements to coffee production such as improved information for farmers as to the susceptibility of their coffee plants to pests and disease, a professionalized coffee seed system, and transparency and traceability for buyers of green, un-roasted coffee.

As of May 2024, Plants of the World Online includes:

• World Checklist of Rubiaceae
• Coffee & Conservation