Scientific Latin: how a species name is built

A scientific name is two Latin words in a grammatical relationship. The genus is a noun with a fixed gender; the epithet after it is usually an adjective agreeing with that noun, sometimes a second noun or a genitive. Learn the three patterns and a field guide stops being vocabulary and starts being information.

Why Latin: 1753 and 1758

Before Linnaeus, a plant's name was a description, a Latin phrase of many words that no two authors agreed on:

• Physalis annua ramosissima, ramis angulosis glabris, foliis dentato-serratis - the old phrase-name.
• Physalis angulata - Linnaeus's two words for the same plant.

Carl Linnaeus did not invent Latin names. He made the two-word name the rule and applied it to every plant and animal he described, in two books that are still the legal starting lines:

The botanical and zoological codes count from those books (for most groups), and of two names for one species the older wins. Marsh named Apatosaurus in 1877 and Brontosaurus in 1879; for a century the 1877 name took the bones, until a 2015 study split them again.

Other species got a description of their features. For Homo sapiens Linnaeus wrote nosce te ipsum: know yourself.

How a species name is written

Two words, two jobs, and four rules of typography:

The epithet stays lower case even when it honours a person: Rafflesia arnoldii is named for Joseph Arnold. And the epithet alone names nothing: there are many species called vulgaris, and only one Thymus vulgaris.

Zoologists call the system binominal nomenclature; botanists say binomial. The two codes have been failing to agree on small things for a century.

The epithet as an adjective

Most epithets are adjectives, and an adjective agrees with its noun in gender. The genus decides the ending: one adjective, three genders.

Two patterns are at work:

• officinalis, officinale - third declension: -is for masculine and feminine, -e for neuter.
• sativus, sativa, sativum - like bonus, bona, bonum.

Homo sapiens agrees too, and shows nothing for it. Sapiens, wise, is a present participle of sapere, third declension, with one nominative singular for all three genders. Beginners who assume epithets never change have been looking at the ones that cannot.