Plant Taxonomy - Part 2
Marion Jarratt
Note: This article originally appeared in 'Brigge', the newsletter of the friends of Burrendong Arboretum. The Arboretum is located in the central west of New South Wales, near Wellington.
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Why was the Linnaean system adopted and what was his real legacy?
To answer these questions we should look briefly at his major work Species Plantarum [1753]. It is in this work that he succeeded in regularising the way plants and, in later works, animals are studied. [Although usually associated with plants, Linnaeus devised a classification system for the animal world as well. He actually named over 4,300 animal species and coined the term homo sapiens.]
Linnaeus designated 24 classes into which plants were grouped, based on the number of male reproductive organs - stamens. Each of the first 10 classes were named after the number of stamens, eg. Monandria [literally one man, in this case stamen], Diandra [2 stamens] up to Decandria [10 stamens] The flowers in the eleventh class, Dodecandria, had 12 - 19 stamens and the remaining classes were characterised not only by the number of stamens but their position, whether united or not and those plants with stamens and pistils in separate flowers. The last class was for plants without proper flowers.
Plants in these classes were divided into orders, based on the characteristics of the female reproductive organ, the pistil, then into genera. Morphological characteristics, eg. the description of the plant, became more important at the genus and species level. Actually Linnaeus, once he had devised his system, worked from the bottom up starting with an accurate description of the species.
A sample entry from Species Plantarum is reproduced below. The genus Solidago has been put in Class 19 [Syngenesia] and the species is sempervirens [written in italics on the left hand margin]. The first two lines are the 'diagnostic polynomial', the long descriptive name which indicates how the species differs from other species in the genus. In every entry Linnaeus uses the binomial or shorthand reference as well as this longer botanical description. If he felt that the species was the same, he followed the initial description with additional descriptions cited in other literature [the italicized abbreviations refer to previous publications and page numbers]. In this example there are five additional descriptions which Linnaeus treats as synonyms of his initial polynomial description. He also added the region where the species naturally occurred [in this case, Canada] and, sometimes, again as in this case, extra notes.
Linnaeus' system was eventually widely adopted partly because he made identification of plants so simple and partly because he was such an excellent salesman. His new 'Language of Flowers' was, he boasted, so straightforward that even women could understand it! Determined to make his ideas easily accessible, Linnaeus wrote not only prolifically as he continually refined his system but clearly, with practical instructions about collecting, labelling and growing plants. And he made sure his books were cheap and readily available.
For years he led great troops of botanists [and students] through the Swedish countryside, showing them how easily they could identify plants, until the rector of the University of Uppsala, where Linnaeus was Professor of Medicine [read Botany], banned these enjoyable excursions because 'we [Swedes] cannot, like others, unite the pleasurable and fun with the serious and useful'. Linnaeus also sent his students all over the world on collecting trips. For instance, Solander, one of his disciples accompanied Banks on the Endeavour.
In Britain the new Swedish system was initially slow to catch on. But by the second half of the eighteenth century English translations and commentaries began to appear. Botanists conducted field trips and James Lee, owner of a large nursery in London, produced a guide that made it easy to apply Linnaean ideas to English flowers. One of the first institutions to use it was the British Museum whose first director insisted on adopting the Linnaean system for not only the gardens outside but for the plants and animals displayed inside as well.
However, Linnaeus' actual classification system was essentially artificial because it relied upon only a very few features of the flower [stamens and pistils] as the primary basis for division and this resulted in obvious errors. For instance cacti and pines were grouped together because they had numerous male parts. Linnaeus, himself, realised this but felt it would be a long time before anyone knew enough about nature to devise an entirely natural taxonomy.
In fact his system generally fell out of use within a century of its creation as botanists turned to a more natural system of classification. Darwinian Theory and Mendel's discoveries in genetics led to the 'evolutionary synthesis', an integration
of evolutionary theory, systematics and morphology. More recently plant chemistry, molecular biology and genecology [the documentation of variations between species] has improved the understanding of plant groupings.
But the real Linnaean legacy was his system of naming and describing plants and animals which, essentially, provided a universal, scientific language which is still in use today.
In a period when the scientific world was being flooded with new species; when previous and contemporary literature named and described plants and animals in as many ways as there were authors, Linnaeus created order out of chaos.
Linnaeus developed a system of uniform description, classification and naming which simplified enormously the work of identifying plants and animals. Most importantly, he popularised the use of Binomial Nomenclature - the use of two names only - to identify a plant. He standardised the writing of descriptions to give consistency and developed a number of terms still used in describing plants. Today his use of two word names and descriptive protocols is universal.
Importantly Linnaeus also synthesised the previous literature about all plants and animals known to the western world, determining which descriptions in one work correlated to which descriptions in another work and then including them in his system with its shorthand binomial reference.
Others before Linnaeus had used grouping of species and genera, experimented with binomials, suggested classification systems etc, but none had ever worked on such a grand scale and so comprehensively. It was this that cemented his place in the history of taxonomy.
Just as a footnote you might be interested to know that Linnaeus was the first to recognise that the rings evident on the cross section of a tree trunk are a record of the year to year and season to season growth. He was an ecologist long before the discipline even had a name and his descriptions of the interdependency of species impressed even Darwin. And he was one of the first to recognise the potential of biological control. "Until now' he wrote, 'no one has thought about exterminating insects with insects. Most every insect has its lion which persecutes and exterminates it; these predatory insects ought to be tamed and taken care of so they can purge plants."
A truly remarkable man!
References
A series of monographs on the Internet; Order from Chaos: Linnaeus Disposes, online exhibition by the Hunt Institute for Botanical Documentation.
Sex, Botany and the Empire - The Story of Carl Linnaeus and Joseph Banks. Patricia Tara. Icon Books 2004.
From 'Brigge', the newsletter of the Friends of Burrendong Arboretum Inc., October 2005.
Australian Plants online - 2008
Association of Societies for Growing Australian Plants
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