In this article, we examine coffee and the coffee plant from a botanical perspective. What is the structure of the plant, what do the roots, leaves, and fruits do? And how do we correctly describe them botanically?
Everyone knows the feeling freshly ground coffee can evoke. Just the thought of it can awaken a desire for coffee. It's not for nothing that it helps to always grind coffee fresh, because the aromas evaporate very quickly.
We place the ground coffee in a portafilter, coffee filter, or French press, pour or press hot water over it, and enjoy. But what are we actually drinking when we drink coffee?
We drink the dried, roasted, ground and brewed seeds of a fruit of the genus Coffea .
In short, we simply call it coffee —but the differences between genus, species, and varieties are vast; many species are inedible, and various varieties do not smell or taste like the familiar beverage we simply call “coffee.”
100% Arabica - old school and meaningless
Coffee packaging is still labeled "100% Arabica," which, firstly, doesn't do justice to the complexity of the product and, secondly, doesn't provide any added value. Distinguishing between species alone is also outdated. The coffee plant is subject to climate change just like other organisms, and so we should expand our vocabulary to understand and describe the coffee of the future.
To ensure that we can continue to drink coffee in the future, despite rising temperatures and unpredictable weather patterns, more research is needed into the further development of the coffee plant - and this includes an in-depth study of the various varieties and species.
Researchers have been working intensively for years to bring new hybrids from the laboratory into the field and scale them up. The simplified distinction between Arabica and non-Arabica (e.g., Robusta) falls far short.
However, botanical taxonomy, the classification of the coffee plant into categories, is not self-explanatory. This is reason enough to break down this important fundamental topic.
Coffee botany
At a lunch with agronomists, I once asked whether the coffee plant was a tree or a shrub. A witty discussion about definitions ensued, with almost everyone agreeing in the end:
The coffee plant is a tree. Trees typically have only one main trunk protruding from the ground. Bushes, on the other hand, have several woody trunks, which can also be pruned individually.
Coffee trees in the agroforestry system in Marcala, Honduras.
From seed to tree
The coffee tree originates from the seed of a fruit. The coffee seed is the actual coffee bean, which can be extracted from a pulped coffee cherry. This seed should be sown relatively fresh, with a moisture content of over 50%.
The seeds are usually thoroughly moistened in a substrate of sand and loose soil and germinated. After a month, the hypocotyl, the lowest section of the stem, has already formed, between the still-fine roots and the cotyledons. The parchment , also called the horn coat, still covers the cotyledons before they are soon shed.
After about three months, the seedlings are ready to be transplanted into individual plastic bags filled with soil. Once they've reached a height of approximately 40 cm and have a well-developed root system, they're transplanted into the field and planted after about a year.
From sapling to tree
It typically takes three years from germinating seed to the first small harvest. However, hybrids, i.e., plants resulting from cross-breeding of different species, can produce fruit in as little as two years. This acceleration of the growth process brings greater efficiency to coffee farm planning.
A coffee tree can produce fruit for several decades if well cared for. However, production gradually declines after about 20 years. The tree trunks become increasingly woody, and the fruit yield decreases. Furthermore, trees can become more susceptible to disease as they age.
In his 2004 classic, Wintgens writes that a coffee plant in production is barely older than 30 years. However, discussions with trading companies and producers revealed that their plants were barely older than 20 years, and that 30 years may have been correct "some time ago." The climatic challenges facing coffee plants have become more dramatic, and they are subject to massive change.
On this farm in Santa Barbara, Honduras, temperatures reach up to 33 degrees Celsius. This is too high for coffee production. The focus on agroforestry is becoming increasingly important.
Rather, discussions with producers revealed that more than 90% of their trees are less than 15 years old. The Norcafé cooperative in Peru encourages its members to replace plants after 15 years. The trees would then invest increasingly more in wood growth and less in fruit production, and the yield would gradually decline. The trees would continue to produce fruit for another 15 years, but not at an efficient rate.
The root system of the coffee tree
The coffee plant is a perennial plant. Without a well-developed root system, the plant would not be able to guarantee its nutrient and water supply and ultimately produce reliable fruit. A healthy root system is essential for tree health.
Wintgens says that the taproot can reach up to 1m deep into the soil. Loose soils allow the root system of a single coffee plant to penetrate up to 15m3 of soil with its roots. (Wintgens, p. 7)
The function of roots is clear: they absorb water and transport it throughout the plant. At the same time, water acts as a solvent, transporting gas and minerals to the cells and organs. The root system functions as a storage facility for carbohydrates and produces the plant's own growth hormones.
A wide variety of factors influence the shape and growth of a root system: the species and varieties, the quantity of fruit, the resistance of the above-ground part, attacks by fungi or diseases, the distance to the next plant, the soil condition and health, and the water content in the soil.
Just because we can't see the roots doesn't mean they shouldn't be in our consciousness. The development of the root systems in the coffee plant, and other trees, is impressive—and reveals quite accurately what has happened, or is currently happening, above ground. Root systems are like both an ECG and a library.
The root types of the coffee plant
The taproot
At its full developmental stage, the coffee tree has a taproot that extends vertically into the soil, up to half a meter deep. This root is the largest and clearly demonstrates why we call it a tree. If this taproot is not planted straight at a young age, it can become twisted and hardened, and the tree won't grow as planned.
Secondary roots and fine roots
The axial roots are the roots that penetrate the deepest into the soil and extend up to 3 meters in all directions. The lateral roots run parallel to the soil, remain superficial, and, depending on planting density, come into contact with neighboring roots. The fine roots, or hairy roots, are roots of varying lengths and are distributed among the secondary roots. They are primarily responsible for supplying the plant with minerals.
Coffee Farm Training, Nicaragua. Agronomist Oscar shows off a massive taproot.
leaves
As with other trees, the leaves tell us which coffee species or variety we're dealing with. The size, shape, thickness, and curvature are all indicators that help us analyze the plant.
I remember well when Don Oscar, agronomist from Costa Rica, said at the 2019 Coffee Farm Training in Nicaragua:
"Leaves aren't just for photosynthesis. Leaves talk to us. The coffee tree needs leaves to communicate with us. They show us how the coffee tree is doing."
In fact, if you look closely at leaves, you will see more and more details.
According to Wintgens, a fully grown coffee tree produces between 22 and 45 square meters of leaves. The leaves are fully grown after about 35 days, before they fall off at about 10 months, and the tree produces new leaves.
Wintgens also writes that a coffee tree evaporates approximately 6g of water per square decimetre daily. Assuming a coffee tree has approximately 35 m² of leaves, that would be 3500 dm² times 6g of water = 21l of water.
According to Wintgens, an average coffee tree evaporates about 20 liters per day.
And here we clearly see how important the soil's water retention capacity is for coffee production. Canephora is usually artificially irrigated because it is significantly more susceptible to moisture stress and requires regular irrigation times for the flowers to develop as desired.
From blossom to fruit
The coffee fruits are called coffee cherries—however, unlike the usual cherries, the flesh isn't eaten and the seeds discarded, but the other way around. A cherry usually contains two seeds facing each other—these are the future coffee beans.
A blossom just before opening (right) and approximately six-month-old coffee cherries in Nicaragua.
During a trip to Costa Rica, a producer once told me he still had to visit his children. "There are so many of them now"—I wanted to be discreet and ask for the exact number. It soon became clear, however, that by "niños" he meant his coffee plants. The analogies go even further, as most Arabica plants take about nine months from flowering to producing ripe coffee cherries, while Canephoras can take up to 11 months.
The coffee plant actually depends on stable weather patterns to develop well. However, these weather patterns have been shifting for years, requiring considerable flexibility from producers each year. Ideally, it would be dry after harvest, causing the coffee tree to feel stressed: the bud would then interrupt its dormancy, forced to survive.
During the dry period, the plant drastically slows down its metabolism. It constricts its capillaries and prepares for the first rain. When it arrives, the plant is ready to absorb water quickly, and cell division in the bud occurs just three to four days later.
Depending on the amount of precipitation, sometimes more, sometimes fewer buds are activated. Several short, staggered downpours result in less uniform ripening and ultimately require the coffee cherries to be harvested at different times. In short, unstable weather patterns lead to more picking work.
Coffee types, coffee varieties & hybrids.
The majority of coffee consumed is still Arabica. For several years, the ratio has settled at 40/60 . 40% of the coffee grown is Canephora (commonly known as Robusta), and 60% is Arabica. At the same time, however, coffee consumption is also increasing, so the proportions of both varieties are growing simultaneously, but so far they have remained at the 40/60 ratio.
However, rising temperatures and rapidly changing weather patterns will accelerate the increase in the proportion of Canephora, as well as that of hybrids: a special form of crossbreeding in which two genetically distinct lines are crossed.
The " Marsellesa " hybrid, for example, which we cultivate extensively in Nicaragua, is a cross between the " Villa Sarchi " and "Timor Hybrid 823/2" varieties. These are two varieties that would rarely come into contact "naturally" in the field. Marsellesa was developed by CIRAD, the French Agricultural Research Center, and tested for more than ten years in various Central American countries before the hybrid was launched on the market.
At World Coffee Research, you will find the most commonly cultivated coffee varieties catalogued and classified by origin.
While Arabica and Robusta have probably been the most commonly used terms in the coffee industry to date, this is likely to change in the coming years. Coffee production is massively affected by climate change, which, among other things, continues to accelerate research into new hybrids and varieties.
To classify the new terms, we have collected all the commonly used ones and categorized them taxonomically : the classification into systematic categories. The first person to botanically classify Arabica coffee was the Swede Carl von Linne. He laid the foundation for modern botanical and zoological taxonomy.
Before Linnaeus created the basic classification system for plants in seniem Species Plantarum in 1753, coffee was first classified by Jussieu in 1713:
Jasminum arabicum, laurio folio, cujus femen apudnos coffee deciur ( Arab Jasmine, with laurel type leaves, the beans of which we call coffee ) (Wintgens 2009)
If we take Linnaeus' system of plant classification and insert the coffee terms we know, the coffee taxonomy looks like this.
Coffee Taxonomy
Download poster as PDF
Coffee TaxonomyWhat happens next?
In the next articles, I will write about the differences between the most widely cultivated varieties, Arabica and Canephora, their future viability, and what research is contributing to this.
