EEB337H1 - Families of Vascular Plants

Linnaeus' Sexual System1


Carl Linnaeus (1707-1778) revolutionized the way in which scientific names are applied to plants, fungi, and animals in his 1753 publication, Species plantarum. Click here for an online exhibition on Linnaeus' classification of the whole of nature (you have to accept the conditions of use before entering the site).
  • Without having intended to do so at the time, Linnaeus introduced the system of two-part names ("binomials," consisting of a generic name and a specific epithet; i.e. genus and species) for particular kinds of plants, or species, that remains in use today.
  • Prior to Linnaeus, the names used by scientists to designate particular kinds of plants were whole phrases, such as "annual, much-branched Physalis, with strongly-angled, glabrous branches and leaves with sawtoothed edges." The Linnaean binomial for the same plant is simply Physalis angulata.
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Although binomials are a valuable shorthand, what probably contributed even more to the success of the Species plantarum was the ease with which it could be used to identify plants.
  • This was because of the 'Sexual System' that Linnaeus had devised earlier, and published in his Systema Naturae (1735).
  • As shown below (in the engravings of Georg Dionysius Ehret, published by him in 1736), by means of this system virtually any plant can be assigned to one of 24 classes based on the construction of its reproductive structures, in particular the number and arrangement of the male parts (stamens).
  • Within each class the plant is then assigned to an order based on the number of female parts (pistils). Pigeon-holed in this way, there are many fewer possibilities to be considered in then making an identification.
  • Click here to see an example of how this system could be used to classify a small, attractive North American genus named after the twelve Olympian gods.
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Linnaeus in his Lapp costume

Characters of the Classes

Orders

Orders are taken from the females or pistils, as classes were from the males or stamens...

Monogynia, Digynia, etc.

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An example; Dodecatheon L.

The American cowslip, D. meadia L. (Pentandria Monogynia), was described by Erasmus Darwin (Charles' grandfather) in his popularization of the Linnaean system, The Botanic Garden (1791), as follows:

MEADIA'S soft chains five suppliant beaux confess,
And hand in hand the laughing belle address;
Alike to all, she bows with wanton air,
Rolls her dark eye, and waves her golden hair.

Thus, this verse describes how Dodecatheon belongs in Class Pentandria ("five beaux"), Order Monogynia ("the laughing belle"). Users of Linnaeus' system needed merely to be able to understand the construction of a flower, and be able to count, in order to assign an unknown plant to its class and order.

[Dodecatheon sp. - Photo M. Ferguson]

Dodecatheon sp.
Photo M. Ferguson,
Royal Ontario Museum 1998

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Source

W. T. Stearn's "An Introduction to the Species Plantarum and cognate botanical works of Carl Linnaeus," 1957.

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Please send your comments to tim.dickinson@utoronto.ca; last updated 06-May-2008