The Coffee Plant

Anatomy of the Coffee Fruit and Bean

The coffee fruit can be divided into two main parts, the pericarp and the seed.

Adapted from Borém, 2008

Pericarp
The pericarp is the outer three layers of the fruit: the exocarp (skin), mesocarp (mucilage), and endocarp (parchment).

Exocarp (Skin)
The exocarp, also referred to as the peel, skin, or epicarp, is the outermost layer of the coffee fruit. It is formed by a single layer of compact parenchyma cells (cells with thin primary walls that contain chloroplasts and are capable of absorbing water). The color of the exocarp at the beginning of fruit development is green due to the presence of chloroplasts which then disappear as the fruit matures (Castro and Marracini, 2006). Color upon maturation depends upon coffee variety, but is most commonly red or yellow. Red skin color comes from anthocyanin pigments, while yellow skin color is attributed to luteolin (Borem, 2008).

Mesocarp (Mucilage)
The mesocarp, also referred to as the mucilage, is the flesh of the coffee fruit. While “pulp” can sometimes refer to solely the mesocarp, the term usually refers to a combination of the exocarp and part of the mesocarp removed during pulping.  In unripe coffee fruit, the tissue is rigid. With maturation, pectolytic enzymes break down pectic chains, resulting in an insoluble hydrogel that is rich in sugars and pectins (Borem, 2008). Studies have shown that the mucilage/water ratio of the mesocarp increases as growing altitude increases (Borem, 2008). In the wet processing method, this mucilage layer is removed through controlled fermentation. In the dry method, the mucilage, along with the exocarp and endocarp, is left intact during drying (see Harvest and Post-harvest) for more information).

Endocarp (Parchment)
The endocarp, or parchment, is the innermost layer of the pericarp and is the hull that envelops the coffee bean. It is formed of three to seven layers of sclerenchyma cells (fibrous cells that serve as the principal support cells in plants). The cells of the endocarp harden during coffee fruit maturation, thus limiting the final size of the coffee seed, or bean. In arabica coffee, the average weight of the parchment with 11% moisture content is around 3.8% of total coffee fruit weight (Wilbaux, 1961, as cited in Borém, 2008).

Seed
The coffee seed, or bean, comprises a silver skin, an endosperm, and an embryo. Coffee seed (bean) sizes vary; however, they average 10mm long and 6mm wide.

Silver Skin
The silver skin, also called the perisperm or spermoderm, is the outermost layer that wraps the seed. It is formed from the nucellus, or central portion, of the ovule. Generally some remnants of the silver skin remain on the bean pre-roast, and come off during coffee roasting as chaff. The silver skin may be polished off of the bean; however, it is generally accepted that this diminishes coffee flavor. It has also been proposed that the presence of a large amount of silver skin on milled coffee is a sign of coffee picked before its ideal ripeness. In some regions the silver skin may take on a darker hue, in which case the beans are called fox beans. Fox beans are not considered to be a defect.

Endosperm
The endosperm is the principal reserve tissue of the seed, and is composed of only one tissue, though the cells in the exterior and interior portion of the endosperm vary in oil content and cell wall thickness. The chemical content of the endosperm is of utmost importance since it is the precursor to the flavor and aroma of roasted coffee. The chemical compounds found in the endosperm can be classifed as soluble or insoluble in water. The water-soluble compounds are caffeine, trigonelline, nicotinic acid (niacin), at least 18 chlorogenic acids, mono-, di-, and oligosaccharides, some proteins and minerals, and carboxylic acids. Components insoluble in water include cellulose, polysaccharides, lignin, and hemicullulose, as well as some proteins, minerals, and lipids (Borem, 2008).

Embryo
The embyro is composed of a hypocotyl (embryo axis) and two cotyledons and is 3-4 mm long (Wintgens, 2009). Coffee seeds germinate via epigeal germination, in which the hypocotyl elongates and pushes the seed upward above ground. The original cotyledons stay underground; however, new cotyledons will form.

Adapted from Wintgens, 2009

Bibliography:

Borem, F. ed. Pos-colheita do cafe. Lavras: Editora UFLA, 2008.
Castro, R. & Marraccini, P. “Cytology, biochemistry and molecular changes during coffee fruit development.” Brazilian Journal of Plant Physiology, vol. 18, Jan – Mar 2006.
Wintgens, J. N. Coffee: Growing, Processing, Sunstainable Production (2nd ed.)Weinhem: Wiley-VCH, 2009.

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Cultivars

Typica (C. arabica L. cv. Arábica)

The plant that Linnaeus initially classified as Coffea arabica was, in fact, the Typica variety.  It is from this variety that most arabica coffee plants are derived.  Typica has relatively lower yields, but is known for its good quality in the cup.

Bourbon – Yellow  (C. arabica L. cv. Bourbon Amarelo)
First discovered in 1930 outside of Pederneiras, Sao Paulo, Brazil, Yellow Bourbon is thought to be either a natural hybrid of Red Bourbon and Botucatu Yellow or a natural mutation of Red Bourbon.  The plant is tall with yellow fruit, early maturation (20-30 days earlier than Mundo Novo), average screen size of 16, and is susceptible to leaf rust.  The early maturation is especially favorable in higher altitudes or lower temperatures where maturation is delayed (Fazuoli et al., 2000).  It was released commercially by the IAC in 1945 and has developed a reputation for excellent cup quality, including bright acidity and elevated sweetness.

Botucatu Yellow
In 1871, a natural mutation was discovered in a Typica field outside the city of Botucatu, Sao Paulo, Brazil that produced yellow fruit instead of red fruit (Oliveira and Maluf, 2007). It was called Amarelo do Botucatu, or “Yellow from Botucatu.” Due to lack of productivity,the plant was not introduced on a large commercial scale, however it is thought the its natural hybridization with Red Bourbon led to the Yellow Bourbon cultivar (Oliveira and Maluf, 2007).

Catuai – Red and Yellow
In 1949, the Instituto Agronomico de Campinas (IAC) crossed Mundo Novo and  Red Caturra with the intent of combining the rust-resistance of Mundo Novo with the small size and high productivity of Caturra (Oliveira and Maluf, 2007). After several generations, Red Catuai and Yellow Catuai were released for commercial production. Catuai cultivar has shorter plant height, short internodes, mid to late maturation,  average of 16 screen size, and moderate susceptability to leaf rust (Fazuoli et al., 2000). It is recommended for dense planting. Several lines of Catuai have developed, and it has become one of the most planted cultivars throughout Latin America.

Caturra (C. arabica L. cv. Caturra)
natural mutation of the Bourbon variety discovered near Manhumirim in the Serra do Caparao range that divides the Brazilian states of Minas Gerais and Espirito Santo  (CARVALHO et al., 1984). It was sent to the Instituto Agronomica de Campinas (IAC) in 1937, though it is likely that the mutation occurred at least 22 years prior to being received by the IAC (Oliveira & Pereira, 2008). The Caturra cultivar displays compact growth (short internodes) with early fruit maturation, high productivity, and average screen size of 16. Since Caturra was the first mutation discovered that offered decreased sizewith high production capacity, it was used by the IAC starting in the 1930’s for the genetic improvement of coffee and is the basis of many coffee cultivars commercially grown today. In Brazil, Caturra was not introduced commercially due to its lack of vigor, susceptibility to coffee leaf rust, and the fact that it enters into degeneration after several harvests. In the higher altitudes of Colombia and Central America, however, Caturra has flourished. Cup quality is considered to be moderate to good, however not as good a Bourbon or Typica. Caturra berries can be either red or yellow (Yellow Caturra and Red Caturra).

Icatu
Due to the threat of coffee lead rust, the IAC focused on developing a rust-resistant plant.  They acheived this by crossing of tetraploid C. Canephora  cv. Robusta (Robusta coffee with its chromosome number artificially doubled) with  C. arabica Bourbon, then backcrossing with Mundo Novo (Illy & Vianna, 1995) (Oliveira & Pereira, 2008). Icatu Tall height, red and yellow fruit, middle to late maturation, average screen size of 17, moderately resistant to leaf rust, medium to good cup quality  (Fazuoli et al., 2000) (Illy & Vianna, 1995).

Maragogipe
A natural mutation of Typica variety that first appeared near Maragogipe, Bahia, Brazil. All plant aspects of this mutation are larger than Typica, including tall plant height, large convex leaves that are broad at the base, and large bean size. Both yellow and red fruit varieties exist. Maragogipe also has a decreased level of caffeine, 0.6% vs 1.3% for Arabica (Wintgens, 2007). Due to its lower productivity it was not released for large scale commercial production in Brazil, but is now more commonly found in Nicaragua, Guatemala, and Mexico.  It has mild cup qualities.

Mundo Novo  (C. arabica L. cv. Mundo Novo)
A natural cross of Red Bourbon and Sumatra first discovered in Mineiros do Tiete, Sao Paulo, Brazil (Oliveira & Pereira, 2008). Seeds of this natural hybrid were planted and selected in Mundo Novo, Sao Paulo, Brazil, now named Urupês. Mundo Novo is characterized by tall height, red fruit, middle maturation time, average screen size of 17, good vegetative vigor, and high productivity.

What is the difference between a varietal and a cultivar?
In coffee the term “varietal” is often used to refer to the origin of the coffee. For instance, a Cerrado is a coffee from the Cerrado region of Minas Gerais, Brazil, and is most likely a sweet and full-bodied coffee. This ambiguity is on its way out as this use of “varietal” is being replaced by the term “single origin.”

In wine, a “varietal” is  a wine made from a single grape variety. For instance a bottle of Merlot wine is made from wine derived from the Merlot grape, thus it is a varietal.

In botany, a “varietal” is a plant type that occured naturally through cross-pollination, mutation, or adaption. Most varieties are true to type (their offspring will possess same characteristics as parent plants) A variety is always italicized, written in lower case, and oftentimes is proceeded by “var.” Cultivar is short for “cultivated variety,” and cultivars are plants that do/did not occur naturally, but rather have been bred for certain characteristics. Cultivars generally do not grow true to type, and must be propogated by other means. Almost all of the world’s food crops have been bred for certain traits and are therefore cultivars. Cultivar names are enclosed in single quotes ‘dsdsds,’ are never in italics, and are sometimes proceeded by the abbreviation cv. Two examples of common cultivars are Granny Smith (Malus ‘Granny Smith’) and Red Delicious (Malus ‘Red Delicious’) apples.

Bibliography

Carvalho, A.; Medina Filho, H. P.; Fazuoli, L. C.; Costa, W. M. . Hereditariedade do porte reduzido do cultivar Caturra. Genética de Coffea. XXVI  Bragantia, Campinas, v.43, n.2, p. 443-458, 1984.

Fazuoli, L.C; Medina Filho, H.P., Filho, O.G., Goncalves, W., Silvarolla, M.B., Gallo, P.B. Cultivares de Cafe Selecionadas Pelo Instituto Agronomico de    Campinas. 2000 Simposio de Pesquisa dos Cafes do Brasil, 488-493. http://www.sbicafe.ufv.br/bitstream/handle/10820/58/155537_Art128f.pdf?sequence=1

Oliveira, A.C., Maluf, Mirian. Diversidade em Coffea sp. O Agronomico, Capinas 59(1), 22-24, 2007.

Oliveira, A.C.; Pereira, A.A. (2008). Cultivares de Cafe Suscetiveis a Ferrugem Indicadas Para Plantio em Minas Gerais. Circular Tecnica(33), 1-5. Belo Horizonte: EPAMIG.

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Pests and Diseases

As with any other agricultural crop, the coffee plant can suffer from attacks by pests and diseases. Below are a few examples of each, and how they can affect quality, yield, and cost of coffee beans.

PESTS

Black Twig Borer (Xylosandrus compactus Eichhoff)

The black twig borer is native to Asia where it is a serious pest of Robusta coffee, but has spread to coffee growing regions throughout the world where it attacks Arabica coffee as well. Females bore into branches, twigs, and suckers, leaving a pin-hole sized entry. The plant is destroyed through tunneling as well as pathogens introduced by the borer. The black twig borer thrives in humid conditions since humidity facilitates the ambrosia fungus upon which the borer feeds in its younger stages. Infestations can be controlled by pruning (specifically removing unwanted suckers) and shade reduction (Wintgens, 2009).

Cicadas (Quesada gigas, Dorisiana drewseni, Carineta fascicuata, Carineta spoliata, Carineta matura)

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Cicadas are often called locusts, though they are actually unrelated. Females lay eggs by cutting into the bark of tree branches and depositing eggs. After hatching, the nymphs falls to the ground where they burrow into the ground and feed from the sap of the tap root and other larger roots. This can cause chlorosis in the outermost leaves of the plant, as well as premature falling of leaves, flowers, and fruits. These systems are more predominant in dry periods (Moraes et al., 2004).

Coffee Borer Beetle (Hypothenemus hampei)

The coffee borer beetle is a small black beetle that bores into the lower portion of the coffee fruit and lays eggs in the seed endosperm. The coffee borer beetle thrives in humid conditions and dense crop spacing. The best means to limit infestations are through proper plant pruning and ensuring that all coffee is harvested and no coffee fruit is left in the fields between harvest.

Coffee Leaf Miner (Leucoptera coffeela)

The coffee leaf miner is a silvery white moth whose larvae penetrate the leaves of coffee plants and feed on the tissues between the epidermis, leaving a hollow area that dries out and results in brown spots. The larvae are around 5 mm long. If not controlled, the coffee leaf miner may cause intense defoliation and loss of production. Infestations are usually greater during hotter and drier periods of the year. The coffee leaf miner was first classified by French entomoligist Felix Edouard Guerin-Meneville in 1842. In Portuguese the Coffee Leaf Miner is commonly called bicho mineiro.

Coffee Red Mite (Oligonychus coffeae) and Southern Red Mite (Oligonychus ilicis McGregor)

The coffee red mite and the southern red mite are both spider mites, around  0.5mm in length and colored a reddish-orange with dark spots. Attacks, which are generally isolated, occur on the upper surface of mature coffee leaves. The leaves lose their shine and turn a brown, yellow, or bronze color. In dry and hot periods, the foliar damage can lead to premature defoliation of the plant.

Coffee White Stem Borer (Xylotrechus quadripes Chevrolat)

The larvae of the coffee white stem borer mine into the stem of coffee plants causing fragility in the plant. Younger plants usually usually die within one season of the infestation while older plants can survive for several seasons, however, with decreased yields and greater susceptbillity to disease. The coffee white stem borer is found in Asia, where it is considered one of the most devastating pests to arabica coffee production.

Green Scale (Coccus viridis Green)

Green Scale, also called Coffee Green Scales, is a pale green color with several black spots on its back. Each female lays 50-600 eggs which then hatch within hours (Wintgens, 2009). Like mealybugs, the scale secretes a honeydew that creates a film on the plant leaves. This attracts ants and other insects, and can lead to the growth of a sooty mold that decreases photosynthesis and depreciates the value of the coffee. Control measures are similar to those for mealybugs.

Mealybugs (Planococcus spp.) e.g. Coffee Mealybug (Plannococcus lilacinus Cockerell) and Citrus Mealybug (Planococcus citri Risso

Mealybugs attack arabica and robusta coffee plants, among others. They can attack the plant at any location, including branches, nodes, leaves, roots, and flower clusters. The mealybugs secrete a sticky honeydew that both attracts ants and leads to the formation of a black sooty mold which covers the leaves and may affect photosynthesis. Infestations are sporadic; however, they are more common in plantations with non-uniform or limited shade (Wintgens, 2009). The coffee mealybug has been found in Africa, Australia, Asia, and Central and South America. Mealybugs can be controlled by maintaing shade at 30% for arabica and 20-25% for Rubsta (Wintgens, 2009), controlling ant population, the introduction of parasitic wasps, and the use of proper insecticides.

 

Nematodes (Meloidogyne incognita, M. javanica, M. caffeicola, M. arenaria, M. hapla, M. exigua)

Nematodes are worm-like organisms that are 0.1-5mm in length. They attack the root system of plants, feeding on the sap. They can form knots in the roots that inhibit the plant from properly feeding. Symptoms of a nematode infestation are galls, splits, scales and decreased mass in the root system, and chlorosis and defoliation in the upper plant. C. canephora is more resistant to nematode infestations, and thus using seedlings engrafted in C. canephora rootstock is a means of limiting outbreaks.

 

Red Flat Mite (B revipalpus phoenicis Geijskes)

Flat Mite

The red flat mite is a tiny mite (275 microns) and is reddish-orange in color. It is generally found in branches and fruits near the center of the plant. It can be found throughout the year, with populations peaking during dry periods (Moraes et al., 2004). It does not directly harm the plant, but rather transmits viruses to the plant, including the coffee ringspot virus (CoRSV), which in turn causes premature fruit and leaf drop.

 

Soldier Fly (Stratiomyiid Fly) (Chiromyza vittata Wiedemann)

The Stratiomyiid Fly is found in the Sul de Minas (Southern Minas) coffee region, especially in colder parts of the region (Moraes et al., 2004). The larvae attack the root system during the coffee plant’s initial development, thereby reducing production. These attacks also allow the entry of pathogenic fungi such as Fusarium (Waller et al., 2007). The Stratiomyiid Fly is aptly called the mosca-de-raiz, or root fly, in Portuguese.

DISEASES

Bacterial Blight (Pseudomonas syringae pv garcae)

Bacterial Blight, also called Elgon Die-back, was first identified in Garca, Sao Paulo, Brazil, thus its name “garcae.” It normally occurs in seedling nurseries and affects plant leaves and tissue. Leaves initially appear to be water-soaked, followed by the appearance of necrotic brown lesions surrounded by yellow rings. The leaves eventually dry, curl up, blacken and die; however, they do not fall from the tree (Wintgens, 2009).

 

Brown Eyespot & Berry Blotch (Cercospora coffeicola)

The cercospora coffeicola fungus may attack both the leaves and the coffee berry. The infected leaves show tan spots with grayish-white centers. On green berries, the lesions are sunken and are brown in color with an ashy center. They are sometimes encircled by a purple “halo,”  or tissue that has ripened prematurely due to the infection. In red coffee fruit, the lesions are larger, black in color, and can sometimes penetrate all the way to the seed, causing the pulp to adhere to the parchment (Nelson, 2008). Cercospora causes defoliation as well as damage to the coffee fruit.

 

Phoma (Phoma costaricensis Echandi)

Phoma is a soil fungus that can attack the coffee leaves and fruit. Coffee leaves attacked by the fungus will develop black or brown spots; coffee fruit will develop black spots while still green/unripe. Climates that are cold, humid, and windy favor phoma attacks, which generally occur after blooming and before fruit ripening. Effects can be mitigated through the use of wind-breaks in areas susceptible to phoma.

 

Coffee Berry Disease – CBD (Colletotrichum kahawae Waller and Bridge)

Coffee berry disease (CBD) is caused by the fungus Colletotrichum kahawae. CBD was first documented in 1922 in Kenya. It attacks coffee berries at any point  in their maturation; however, only symptoms detected on young berries can be clearly diagnosed (Wintgens, 2009). The disease can appear in “active” form and “scab” form. In the “active” form, dark-colored indented spots appear on the coffee bean and are followed by a pale pink crust as the spores develop. The berry is destroyed in a matter of days and reduced to an empty, blackened and dried out pouch. The “scab” form is a much milder attack where several small concave spots form on the berry.

 

Coffee Rust (Hemileia vastatrix)

Coffee rust is fungus that attacks coffee plants. Its color can range from yellow to orange. First documented in Kenya in 1861, it is now known to be in nearly every coffee-producing region in the world. Spores set in on the underside of leaves and can cause severe defoliation, impaired photosynthesis, and a decrease in crop production. Copper-based chemicals have been somewhat effective in combating coffee rust, as have fungicides such as Triadimefon, Cyproconazole and Hexaconazole. Due to the historical significance of its destruction, much research has been conducted in genetic resistance to coffee leaf rust resulting in the development of such varieties as Catimor, Colombia, Ruiru 11, and Icatu.

 

Bibliography

Borem, F. ed. Pos-colheita do cafe. Lavras: Editora UFLA, 2008.
Moraes, J et al. Estrategias e Taticas de Manejo Integrado de Pragas do Cafeeiro. Lavras: Editora UFLA, 2004.
Nelson, S.C. Cercospora Leaf Spot and Berry Blotch of Coffee. Plant Disease. PD-41, 2008.
Waller, J et al. Coffee Pests, Diseases, and Their Management. Oxfordshire: CABI, 2007.
Wintgens, J. N. Coffee: Growing, Processing, Sunstainable Production (2nd ed.)Weinhem: Wiley-VCH, 2009.


Coffee Taxonomy

Brief History of Coffee Classification

The first recorded taxonomic description of coffee was by French naturalist Antoine de Jussieu, who described a coffee plant from the botanical garden of Amsterdam as “Jasminum arabicanum, lauri folio, cujus femen apudnos coffee decir” (“Arab jasmine, with laurel type leaves, the beans of which we can call coffee”) (Wintgens, 2009).  In 1737 Linnaeus classified coffee into a separate genus, Coffea, in his Hortus Cliffortianus, a catalog of the plants that wealthy Amsterdam banker and hobby botanist George Clifford III (thus the “Cliffortianus”) had accumulated at his country estate, Hartekamp. In his Species Plantarum Linnaeus again classified coffee as a separate genus; Coffea, however, maintained in the epithet the false assumption that the plant originated in the Arabian Peninsula, rather than East Africa.

Throughout the second half of the nineteenth century many new Coffea species were discovered in Africa (Clifford & Wilson, 1985). Full taxonomies of coffee were made by Froehner (1898), Chevalier (1938, 1947) and Lebrun (1941) (Wintgens, 2009). Auguste Jean Baptiste Chevalier’s taxonomy,  published as Les Cafeiers du Globe in 1947, grouped the species of Coffea into four sections: Eucoffea, Mascarocoffea, Argocoffea, and Paracoffea. These divisions have since been disputed, and recently Leroy (1980) has suggested creating separate genera for Agrocoffea and Paracoffea (Leroy, 1980). Of note is that the major commercial species of coffee, C. arabica and C. canephora, fall into Eucoffea and Mascarocoffea species and have the commonality of having caffeine.

The most recent taxonomy of coffee, published in 2006 in the Botanical Journal of the Linnean Society 152, lists 103 species of Coffea and can be purchased online from Wiley Online Library.

Coffee Taxonomy

Domain: Eukaryota

Kingdom: Plantae

Division (Phylum): Anthophyta or Magnoliophyta
Also known as angiosperms, flowering plants that produce fruits with seeds that contain an endosperm.

Class: Magnoliopsida
This class comprises dicots, or plants that generally contain two cotyledons, have vascular bundles that only occur in one ring in the stem, and flower parts occuring in sets of five. This class contains six subclasses: Magnoliidae, Hamamelidae, Caryophyllidae, Dilleniidae, Rosidae, and Asterdae (Mauseth, 2003).

Subclass: Asteridae 
Most plants of the Asterdae subclass have 3 common characteristics: Petals are fused together into a tube, there are fewer stamens than petal lobes, and stamens alternate with petals. Many plants in this subclass contain iridoid compounds which rarely found outside the Asteridae subclass. Several important medicinal plants are found in this subclass such as the Cinchona tree, source of quinine, and Vinca, or periwinkle, that has documented anti-cancer properties (Mauseth, 2003).

Order: Rubiales

Family: Rubiaceae
Variously called the Madder family since the family derives its name from the madder (whose scientific name is Rubia tinctoria), the Bedstraw Family, or the Coffee Family. Other genera besides coffea include GardeniaCinchona L.(which contains the anti-malarial alkaloid quinine), Galium L (most species are known as bedstraw) and Morinda L.

Genus: Coffea L. 
Shrubs or small trees native to subtropical Africa and southern Asia.

Species: Coffea arabica, Coffea canephora

Note: This coffee taxonomy is based on Morphology of Plants and Fungi (1987) by Bold, Alexopoulos, and Delevoryas (see Sources below).

Taxonomic Categories Defined

Domain: 
The highest taxonomic rank of life. In 1990 Carl Woese introduced a classification above Kingdom called “Domain,” and defined three types of domains: 1. Bacteria: Single-cell prokaryote (lack cell nucleus) organisms. The Domain “Bacteria” has one kingdom, also called Bacteria.
2. Archaea: Single cell organisms that lack a cell nucleus and any other organelles.
3. Eukaryotes: Organisms comprised of cells that contain a nucleus.

Kingdom: 
There are six widely accepted kingdoms and they are: Bacteria, Archaea, Protista, Plantae, Fungi, and Animalia.

Division (Phylum): 
Note that division and phylum  refer to the same taxonomic level, with phylum being used in botanical classification. Division names end in –phyta.

Class: Class names end in –opsida.

Subclass: Subclass names end in -idae.

Order: Order names end in -ales.

Family: There is general agreement as to which genera belong to which families. The reason for this is likely the long evolutionary line of each family. Family names end in -aceae. Examples of families are banana (Musaceae), maple (Aceraceae), pepper (Piperaceae), and ginger (Zingiberaceae).

Genus: Members of similar species. Criteria for what defines a genera (the singular form of the plural “genus”) is subjective and often disputed.

Species: The most fundamental level of classification. Plants are of the same species if they can interbreed. Members of different species cannot interbreed.

FAQ’s

How do you pronounce rubiaceae?
The most common pronunciation is “ruby a-c-e”

What does the “L.” after coffea arabica mean (see above)?
The name of a species may be followed by the name of the author that first published a valid description of that species. “L.” stands for Linnaeus. Here is the wikipedia link to standard author abbreviations accepted in Botany.

Why “arabica?” 
Linnaeus introduced the binomial classification as a simple and clear means of identifying species. Each species receives two names. The first is the name of the genus and begins with a capital letter. The second name, called the epithet, can often be descriptive, describing the origin or a characteristic of the species. An example of this is Lupinus texensis, or Texas Bluebonnet. Since Linnaeus thought that the coffee plant was native to the arabian peninsula (coffee, in fact, had arrived in Holland from modern-day Yemen), he added the epithet arabica.

Sources:

Mauseth, J.D. Botany: An Introduction to Plant Biology (3rd ed.). Sudbury: Jones and Barlett Publishers, Inc, 2003.
Wintgens, J. N. Coffee: Growing, Processing, Sunstainable Production (2nd ed.)Weinhem: Wiley-VCH, 2009.
Linnaeus, Carl. Hortus Cliffortianus. 
Bold, H., Alexopoulos, C., & Delevoryas, T. Morphology of Plants and Fungi (4th ed.). New York: Harper & Row, 1980.
Mendes, A. & Guimaraes, R. Genetica e Melhoramento do Cafeeira. Lavras: Editora UFLA, 2001.
Leroy, J.F. “Evolution et taxogenese chez les cafeiers. Hypothese suure leur origine.” Comptes Rendus de l’Academie des Sciences, Paris, 291, 593-6, 1980.

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