Conventional nomenclature

Conventional nomenclature


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Conventional Nomenclature—
How to Write Botanical Names

Botanists—and gardeners—from all over the world, regardless of native tongue, use the same scientific name to identify a particular plant. By consistently using scientific names we can communicate more effectively with fellow horticulturists.

There are specific rules regarding how botanical names should be written. Following are some guidelines. (There are a few rare cases where these rules don’t apply.)

When writing a botanical name, the genus name is capitalized, the species is not, and both these words are set in italics (or underlined):

Rosemary: Rosmarinus officinalis

Oregano: Origanum vulgare

Sweet marjoram: Origanum majorana

Varieties. Sometimes a population of plants within a species differs from other members of the species in some significant way—for example, this population may have white flowers instead of the usual blue flowers. This unique population is given a variety name—added in italics after the species name—to distinguish it from other members of the species.

Hollyhock: Alcea rosea

Black-flowered hollyhock: Alcea rosea var. nigra

Eastern flowering dogwood: Cornus florida

Eastern flowering dogwood with red bracts: Cornus florida var. rubra

You may see the name written without the abbreviation "var." inserted, but technically this should be included.

Cultivars. If a variety is created through cultivation—that is, it doesn’t occur as a natural population, but is the results of breeding efforts by horticulturists—then it is called a cultivar (shorthand for cultivated variety). A cultivar is distinguished from a naturally-occurring variety by capitalizing the cultivar name and placing it in single quotes in plain type.

Tall summer phlox: Phlox paniculata

A named cultivar of tall summer phlox: Phlox paniculata ‘Blue Boy’

A named cultivar of eastern flowering dogwood: Cornus florida ‘Bay Beauty’

An older (and now obsolete) way to indicate a cultivar is with the abbreviation cv. instead of the single quotes - for example, Cornus florida cv. Bay Beauty. This method should no longer be used, but is mentioned here for educational purposes.

Hybrids. Hybrids are the result of sexual reproduction between different species. Hybrid plants can occur naturally, but most of the hybrids familiar to gardeners are the result of breeding work. (More about hybrids in Part II of this course.)

Phlox x procumbens is a hybrid resulting from a cross between P. stolonifera (creeping phlox) and P. subulata (moss phlox).

Phlox x procumbens ‘Variegata’ is a hybrid cultivar with variegated foliage.

When listing several species within the same genus, you can write the entire genus name once, then abbreviate it with the first letter followed by a period for the rest of the list. For example, if you are listing a group of junipers you could write Juniperus communis, J. horizontalis, and J. virginiana to denote common juniper, creeping juniper, and eastern red cedar.

Remembering how to spell botanical names is a challenge, but it is important if you want to be able to research a specific plant. Even more challenging is to pronounce them! There are some customary pronunciations—but even these can vary among regions. Since Latin is a "dead" language that is written but no longer spoken, one could argue that there is no "right" way to pronounce names. And besides, even seasoned horticulturists get stumped with unusual names. Remember, you can always spell out a name to avoid confusion.

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Variety or Subspecies
Although species is the basic unit of classification, there can be subgroups in this classification. The term variety (and, for cultivated plants, cultivar) is used to distinguish a certain population within a species that differs from the rest of the group.

The term subspecies is also used to describe a subgroup of a species. Usually, the word subspecies is used to describe a natural population (as opposed to cultivated plants), and often the term describes plants with a particular geographical distribution or ecological range.


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When is a daisy not a daisy?
The common name "daisy" is used to denote many different plants; you can see why scientific names are important!

Shasta daisy: Chrysanthemum superbum or Leucanthemum maximum

Painted daisy (also called pyrethrum daisy): Chrysanthemum coccineum

Nippon daisy: Chrysanthemum nipponicum

Blue-eyed African daisy: Arctotis venusta

Blue daisy (also called marguerite): Felicia amelloides

African daisy: Osteospermum ecklonis

Cape daisy: Dimorphotheca sinuata

Transvaal daisy: Gerbera jamesonii

Dahlberg daisy: Dyssodia tenuiloba

English daisy: Bellis perennis

Gloriosa daisy: Rudbeckia hirta

Swan river daisy: Brachycome iberidifolia


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