In this article, we'll look at coffee and the coffee plant from a botanical perspective. How is the plant structured, what do the roots, leaves, and fruits do? And how do we correctly describe it within botany?
Everyone knows the feeling freshly ground coffee can evoke. Just the thought of it can spark a craving for coffee. It's not for nothing that it's always best to grind coffee fresh, as the aromas dissipate within a very short time.
We put the ground coffee into a portafilter, a coffee filter, or a French Press, pour or press hot water over it, and enjoy. But what are we actually drinking when we drink coffee?
We are drinking the dried, roasted, ground, and brewed seed of a fruit from the genus Coffea.
In short, we simply call it coffee - but the differences between genera, species, and varieties are significant; many species we can't drink at all, and various varieties don't 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 first, doesn't do justice to the complexity of the product, and second, offers no added informational value. The distinction into species alone is also no longer current. The coffee plant is subject to climate change just like other organisms, and so we should expand our vocabulary to be able to understand and describe the coffee of the future.
For us to be able to drink coffee in the future, despite rising temperatures and unpredictable weather patterns, more research is needed on the further development of the coffee plant - and this includes a deeper examination of various varieties and species.
Researchers have been intensively engaged for years in bringing new crosses from the lab to the field and scaling them up. The simplified distinction between Arabica and non-Arabica (e.g., Robusta) falls far too short here.
However, botanical taxonomy, i.e., the classification of the coffee plant into categories, is not self-explanatory. These are reasons enough to break down this important foundational topic.
Coffee Botany
At a lunch with agronomists, I once asked whether the coffee plant was a tree or a shrub. A humorous fundamental discussion about definitions ensued, with almost everyone eventually agreeing:
The coffee plant is a tree. Because trees generally have only one main trunk emerging from the ground. Shrubs, on the other hand, have multiple woody stems that can also be pruned individually.
Coffee trees in an agroforestry system in Marcala, Honduras.
From Seed to Sapling
The coffee tree originates from the seed of a fruit. The coffee seed is the actual coffee bean, which can be extracted from a de-pulped coffee cherry. This seed should be sown relatively fresh with a moisture content of over 50%.
The seeds are usually well-moistened in a substrate of sand and loose soil and allowed to germinate. After a month, the hypocotyl has already formed, the lowest section of the shoot, between the still fine roots and the cotyledons. The pergamino (parchment), also called the horn husk, still covers the cotyledons before they are soon shed.
After about three months, the seedlings are ready to be transplanted into individual plastic bags with soil. When they reach a height of approx. 40cm and have a well-developed root system, they are planted in the field after about 1 year.
From Sapling to Tree
It usually takes three years from germinating seed to the first small harvest. Hybrids, however, meaning a plant resulting from a cross of different species, can produce fruit after just two years. This acceleration of the growth process brings more efficiency to the planning of a coffee farm.
A coffee tree can bear fruit for several decades if it is well cared for. However, production gradually declines after about 20 years. The tree trunks become increasingly woody, and the yield of fruit decreases. In addition, trees at an advanced age can become more susceptible to diseases.
Wintgens writes in his classic from 2004 that a coffee plant in production is rarely older than 30 years. However, in conversations with trading houses and producers, it turned out that their plants are rarely older than 20 years, and that 30 years "might have been correct some time ago." The climatic challenges for coffee plants have become dramatic, and they are subject to massive change.
On this farm in Santa Barbara, Honduras, it gets up to 33 degrees Celsius. This is too high for coffee production. The focus on agroforestry is becoming increasingly important.
Much rather, discussions with producers showed that more than 90% of their tree stock is younger than 15 years. The Norcafé cooperative in Peru encourages its members to replace plants after 15 years. The trees would then invest more in wood growth and less in fruit production, and the yield would gradually decrease. The tree would still bear fruit for another 15 years, but not in a proportion that would be efficient.
The Root System of the Coffee Tree
The coffee plant is a perennial plant. Without a well-developed root system, the plant could not guarantee its nutrient and water supply and ultimately could not reliably bear fruit. A good root system is a basic prerequisite for tree health.
Wintgens states that the taproot can penetrate up to 1m deep into the earth. 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 the roots is clear: they absorb water and transport it within the plant. At the same time, water acts as a solvent, transporting gases and minerals to the cells and organs. The root system functions as a storage for carbohydrates and produces endogenous plant growth hormones.
Various factors influence the shape and extent of a root system. These include the species and varieties, the amount of fruit, the resilience 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 don't see the roots doesn't mean they shouldn't be in our consciousness. The development of the root system in the coffee plant, and other trees, is impressive - and shows quite accurately what has happened above ground, or is happening right now. Root systems are like an ECG and a library at the same time.
The Root Types of the Coffee Plant
The Taproot
In its full developmental stage, the coffee tree has a taproot that penetrates vertically up to a good half meter deep into the soil. This root is the largest root and clearly shows why we speak of a tree. If this taproot is not planted straight at a young age, it can become crooked, harden, and the tree will not grow as planned.
Lateral Roots and Fine Roots
The lateral roots (axial roots) are the roots that penetrate deepest into the soil and develop up to 3m in all directions. The side roots run parallel to the ground, remain superficial, and come into contact with neighboring roots depending on planting density. The fine roots or root hairs are roots of different lengths and distributed along the lateral roots. They are primarily responsible for providing minerals to the plant.
Coffee Farm Training, Nicaragua. Agronomist Oscar shows a massive taproot.
Leaves
From the leaves - as with other trees - we can recognize which coffee species or variety we are dealing with. The size, shape, thickness, and curvature are all indicators that help us analyze the plant.
I clearly remember when Don Oscar, an agronomist from Costa Rica, said during the Coffee Farm Training 2019 in Nicaragua:
"Leaves are not just for photosynthesis. The leaves talk to us. The coffee tree needs its leaves so it can communicate with us. They show us how the coffee tree is doing."
Indeed - those who deliberately look at leaves always see more details.
A mature coffee tree holds between 22 and 45 m2 of leaves, according to Wintgens. After about 35 days, leaves are fully grown, before they fall off at about 10 months and the tree makes new leaves.
Wintgens also writes that a coffee tree evaporates about 6g of water per square decimeter daily. Assuming a coffee tree has about 35 m2 of leaves, that would be 3500dm2, multiplied by 6g of water = 21l of water.
According to Wintgens' data, an average coffee tree thus evaporates about 20l per day.
And here we clearly see how important the soil's water storage capacity is for coffee production. Canephora is generally artificially irrigated, as it is significantly more susceptible to moisture stress and requires regulated irrigation times for the flowers to develop as hoped.
From Flower to Fruit
Coffee fruits are called coffee cherries - however, unlike a familiar cherry, the pulp is not eaten and the seed discarded, but the other way around. Typically, two seeds lie opposite each other within a cherry - these are the future coffee beans.
A flower about to open (right) and about six-month-old coffee cherries in Nicaragua.
On a trip to Costa Rica, a producer once told me he had to visit his children. "There are so many now" - I wanted to be indiscreet and ask for the exact number. But it soon turned out that by "niños" he meant his coffee plants. The analogies go even further, as most Arabica plants require about nine months from flowering to the production of ripe coffee cherries, while Canephoras need up to 11 months.
The coffee plant actually depends on stable weather patterns for good development. However, these weather patterns have been shifting for years, demanding a lot of flexibility from producers annually. Ideally, it would be dry after harvest, so the coffee tree feels stressed: the bud would then interrupt its resting period, as it feels compelled 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 comes, the plant is ready to absorb water quickly, and cell division in the bud occurs just 3 to 4 days later.
Depending on the amount of rainfall, more or fewer buds are activated - several short and staggered showers result in less uniform ripening and ultimately lead to coffee cherries having to be harvested at different times. In short: unstable weather patterns lead to more picking work.
Coffee Varieties, Coffee Varieties & Hybrids.
Still, Arabica coffee is predominantly consumed. For several years, the ratio has settled at 40/60. 40% of cultivated coffee is Canephora (colloquially Robusta), 60% is Arabica. At the same time, more and more coffee is being consumed, so the shares of both varieties are growing simultaneously, but so far remain in the 40/60 ratio.
However, rising temperatures and rapidly changing weather patterns will accelerate the increase in the proportion of Canephora, as well as hybrids: a special form of cross-breeding where 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 hardly come into contact naturally in the field. Marsellesa was developed by CIRAD, the French agricultural research center, and tested for over ten years in various Central American countries before the hybrid was launched on the market.
You can find the most common cultivated coffee varieties cataloged and classified by origin at World Coffee Research.
While Arabica and Robusta have been the most widespread terms in the coffee sector so far, 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 categorize the new terminology, we have collected all common terms and taxonomically recorded them: their classification into systematic categories. The first to botanically classify Arabica coffee was the Swede Carl Linnaeus. He laid the foundation for modern botanical and zoological taxonomy.
Before Linnaeus created the fundamental classification system for plants in his Species Plantarum in 1753, coffee was first somewhat classified in 1713 by Jussieu:
Jasminum arabicum, laurio folio, cujus semen 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 our known coffee terms, coffee taxonomy looks like this.
Coffee Taxonomy
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Coffee TaxonomyWhat's next?
In the next articles, I will write about the differences between the most commonly cultivated species Arabica and Canephora, their future viability, and what research contributes to this.
