Monday, April 15, 2013

Botany Rules 2. Scientific Names, Genus and Species

prickly pear cactus
prickly pear cactus
 As every basic biology class explains, scientific names were created to organize communication about plants and animals. In the 1500s and 1600s, Europeans spread out over the globe and brought back all kinds of unknown organisms. By the early 18th century, they had chaos--lots of organisms and no system of organization. 

Ipomoea pes-caprae, Padre Island, Texas
morning glory, Padre Island, Texas
Ipomoea pes-caprae, Jamaica
morning glory  Happy Grove, Jamaic
    Here’s a purple-flowered morning glory from the beach in from Jamaica and in Texas. Same or different? 

yarrow, Boulder Colorado
yarrow, Boulder Colorado

Yarrow from Narvik, Norway and Boulder, Colorado. Same or different?

yarrow, Narvik Norway


     Linnaeus set up a hierarchical system: groups are made of subgroups made of more subgroups. It was logical and mostly it worked. His hierarchy was Kingdom, Phylum for animals/ Division for plants, Class, Order, Family, Genus and Species.

carrots, Daucus carota
apple branch
apple, Malus domesticus
    Part of making a workable system was deciding what to call the most basic unit, the organism. Linnaeus decided each distinct kind of plant (or animal) would be known by two names that designate genus and species. Apple Malus domestica, carrot Daucus carota, dandelion Taraxacum officinale, and so on.

dandelion, Taraxacum officinale



   In the 1750s, educated Europeans communicated in Latin. When the Roman Empire dominated Europe, everyone spoke Latin and people who read and wrote, read and wrote Latin. During the Middle Ages, education was mainly through the Catholic Church and they used Latin, partly for historical reasons and partly because a single language in the church facilitated communication. By Linneaus’ time, more and more was being written in local languages, but Latin remained a language that most educated people learned. Consequently, Linneaus wasn’t being difficult but, rather, cosmopolitan in setting up the scientific names as Latin names. His native language was Swedish.

   Scientific names are written in italics in an English text because they are treated as being in Latin, a foreign language to English. (See previous blog: Botany Rules 1)

    The first name, the genus, is the larger category. It is always capitalized. It can stand alone. In contrast, the second name separates a particular kind (species) of plant and is never used by itself. No two different plants have identical two-part (binomial) names, but the various members of a genus share the generic name, as in Helianthus annuusHelianthus grosseserratus, and Helianthus petiolaris, the common sunflower, the sawtooth sunflower and the prairie sunflower, respectively. 
Helianthus grosseserratus
sawtooth sunflower,
Helianthus grosseserratus
Helianthus annuus
common sunflower,
Helianthus annuus
Helianthus petiolaris
prairie sunflower,
Helianthus petiolaris
      Likewise different plants can have the same second word in the species name: Salix nigra, black willow, Juglans nigra black walnut and Fraxinus nigra, black ash.  Since nigra means black in Latin, it can’t stand alone: “the black what?" Juglans refers to a number of walnut species so “the fruits of all Juglans are more or less edible” does make sense.  Or, I can say “the plant in the picture is a Helianthus” without specifying which one.

     Note how the adjective form of genus, generic, means a category in English and the adjective of species, specific, means a particular one. 

    Both words, genus and species, form their plurals in English the way they did in Latin: 1 genus, 2 genera; 1 species, 2 species. Economists use specie as the singular, biologists do not. 

    Scientific names don’t have to be multisyllable horrors. They just tend to be. There are some short ones:  Rhus is the genus of sumac, Rhus glabra is smooth sumac, Acer is maple, Acer nigrum black maple, Zea mays corn. Perhaps the long names are because we have over 300,000 plant species and therefore over 300,000 scientific names, with no duplication. 

    Frequently Linnaeus took the name you’d find in a Latin dictionary for the plant and made that the genus name. For example Hordeum for barley, Rosmarinus for rosemary, and Avena for oats. For plants not known in Rome, often the namers of the plant Latinized the common name, for example Nelumbo (from Ceylonese), Cakile (an old Arabic name), Gelsemium (Italian name of that plant) and so on. Some others are intended to be descriptive: Dichondra from the Greek, two (di) and fruit (chondra), Symphoricarpos (composed from Greek symphorein to bear together and carpos fruit, for the clustered berries), Campanula (Latin “little bell”), Cardiospermum (composed from Greek cardios, heart and sperma seed).

      One genus may contain many different species. The species name for a plant indicates genus and species with the second word, called the "specific epithet"--the awkward jargon reinforcing the idea that it never stands alone--treated as modifying the genus. In English we add an adjective to indicate which sunflower: "the common sunflower not the sawtooth sunflower." The two words of the plant's scientitic name function the same way: which HelianthusHelianthus annuus (literally, the annual sunflower, which it is). Helianthus grosseserratus is called the sawtooth sunflower in the USDA plants list: grosseserratus means large serrations. Serrations on a leaf can be called teeth, and so big tooth or sawtooth sunflower. I don't have picture that shows the leaves well, but the leaves have even bigger "teeth" than dandelion leaves. For Helianthus petiolaris, the Latin name draws attention to the long petiole (stem on the leaf). It is a common plant, so it has a better English name, one that refers to its distribution, the prairie sunflower.

Piper nigrum
Piper nigrum, black pepper
   The scientific name is so thoroughly in Latin that endings on the specific epithet change with the gender of the genus name. So Cyperus niger, Juglans nigra and Piper nigrum, black flatsedge black walnut, and black pepper, masculine, feminine and neuter, respectively.

   Some often-used words used for specific epithets are obvious adjectives:  alba white, azurea blue, orientale eastern, minima, small, etc.  Another set refer to the origin of the plant: japonica, floridana, californica. Adding -ensis is another way of doing that: jamaicensis, nebraskensis. Finally, the plant can be named after a person, usually to honor them: parryi from Parry, gerardii from Gerard. These can be very awkward because the proper spelling in Latin for word ending in a consonant used as a possessive (genitive) is with two i’s, so Andropogon gerardii, Gerard’s bluestem, Andropogon hallii Hall’s bluestem. (These two have easier common names, big bluestem and sand bluestem). 

    Modern scientific usage never capitalizes the specific epithet, no matter what. In the past a variety of species were capitalized but not today, which is nice, because it isn’t easy to recognize which ones were capitalized and which were not. 

Cleome serrulata
Rocky Mountain bee plant,
Cleome serrulata
    To save writing so many letters, you can abbreviate the genus name, for example C. serrulata for Cleome serrulata (Rocky Mountain bee plant). To do that, it has to be clear what it refers to.  Usually one looks for the genus starting with that letter most recently mentioned in the text. So I can't abbreviate Chamaecrista fasiculata, partridge pea, until I've written it out once, making it clear that the C. in C. fasiculata doesn't stand for Cleome
Chamaecrista fasiculata, partridge pea
Chamaecrista fasiculata
partridge pea

   In the published literature you see abuses of this, where, especially in graphs, the scientific names were too long so they abbreviated the genus and then nobody checked whether the genus was written out somewhere else. That's fine if you know that S. gardeneri in a paper on Chamaecrista is likely to be Senna, but that's an assumption the authors and editors really shouldn't make. It certainly doesn't assist the busy reader trying to read the article to have to search to find out what the abbreviation refers to. 

    Another common shortcut is writing sp., the abbreviation for species (singular) after the genus name, or spp. (for more than one species). If I write Populus sp., I am saying, “an aspen but I don’t know which one.”  In contrast, Populus spp. would be “several species of aspen.”  The abbreviations sp. and spp. are considered to be English and are not italicized. 

Schizachryium scoparium
Schizachryium scoparium, little bluestem
     Oh, saying scientific names! Latin has no native speakers, so you can pronounce them as you like. If the people you are talking to understand, well, that's the goal. Americans put an American accent on the names, Australians an Australian accent. No problem. The Argentine said “shiz a KEER i um” (run together as a mouthful), where I’d been saying “Shis ACK ri um” (dragged out like a good Midwesterner) for the name spelled Schizachyrium. So we both got a good laugh. It sounded totally different initially, but it was just an accent thing.

References used
Fernald, M.L. 1950. Gray’s Manual of Botany, 8th ed. D. Van Nostrand, Co., New York. 
Lewis, C. T. 1919. A Latin dictionary for schools. American Book Company, New York.

Questions and comments welcome!

I rewrote this post slightly on August 13, 2014 because reader Barry Anderson pointed out that "species name" properly refers to the binomial (for example, Rhus glabra) and that if I want to talk about the glabra part, I should call it the specific epithet. He is correct, so I have made my choice of words above more precise.

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Kathy Keeler, A Wandering Botanist
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