Linnaeus and the plants

”Nine men in the same bride's chamber, with one woman”

This somewhat bold description Linnaeus wrote about plants with nine stamens and one pistil. Those plants were referred to one of the classes in Linnaeus sexual system, the new classification of the plant kingdom. Already as a student Linnaeus gave guided tours in the botanical garden at Uppsala University. As part of the tour he was to present different classification systems, but Linnaeus was not satisfied with the systems of the time. They were based on, for example, the shape of the petals or whether the plant was a tree or a herb.

After having read a book about the sexual life of flowers he reached the conclusion that the stamens and pistils must be the most important characters for classifying the plants.

Linnaeus worked through the plants and formed a system where the plants were divided into 24 classes. The 24th consisted of the plants without flowers, the cryptogams. The sexual system was first presented in Linnaeus’ famous production Systema Naturae from 1735. It was Linnaeus’ goal to include all plants known from the whole world in his sexual system.

The European botanists did not at first accept Linnaeus’ system since it was so totally different from those known to them. Many were also shocked by his comparison with the human sexuality. However, they soon realised how practical it was and the sexual system became a great success. People could easily find out to which class a plant belonged just by counting the stamens.

Despite the great response to the sexual system it soon became outdated since it was an artificial system. Ever since the starting point of the evolution theory scientists do their utmost to find a natural system that mirrors the relationship and development of the species.

It is a natural behaviour to try to systematise things around us. When the amount of information becomes too large we try to sort it and divide it into groups. Long before Linnaeus scientists have made different systems for the living organisms.

About 300 years BC the Greek botanist Theophrastus made a system for the plants. He divided them into four groups: trees, bushes, small shrubs and herbs. Those groups were then further divided in sub groups depending on leaf shape, life span and where they grew. The system of Theophrastus included about 480 named plants.

Around year 77 AD the Greek doctor Dioscorides employed the utility for mankind as a basis for a classification system. His groups included for example aromatic plants, vegetables and medicinal plants. Dioscorides' system was used in books about herbs until the 16th century.

During the 16th century the number of known plants became too large and difficult to handle in the old systems. The scientists had started to be interested in the plants themselves, not only as being useful to mankind. Several new systems were presented but none of them worked really well. Something all systems had in common was that they were based on the appearance of the plants.

When Linnaeus presented his sexual system in 1735 it was a most welcome change. Linnaeus is called the father of modern systematics.

Stamens and pistils are the male and female reproductive organs in flowering plants. They are necessary for the sexual reproduction. Linnaeus talked about them as men and women in their wedding night. The green calyx leaves he called the bride's bed, and the colourful petals the quilt.

The male organs, the stamens, are growing in a ring inside the petals. They occur in different numbers in different plants and are composed of a filament (the stalk) and an anther. The anther keeps the pollen grains and opens when they are ripe. The pollen grains can be transported from one flower to another by for example wind or with the help of an insect.

In the centre of the flower the female organ is found. It can consist of one or several pistils. On the top of the pistil the stigma is found, under it a thin stalk called the style, and at the base the ovary (with ovules inside) that will grow into the fruit with seeds inside. The pollen grains are deposited on the stigma and fertilises the ovules.

Linnaeus was careful to stress the importance of studying the sexual life of flowering plants. Today it has become a discipline of its own, reproduction biology.

Learn more about sex among plants

”The flower is the joy of the plant” Linnaeus called out. In the flower the wedding between stamens and pistils is celebrated. But there were also plants that kept their wedding ceremony secret to the rest of the world.

Flowering plants and conifers constituted the first 23 classes in the sexual system. The 24th and last Linnaeus called Cryptogamia, which means ”secret wedding”. There he lumped together the plants lacking flowers and seeds, among others ferns, mosses, algae, fungi and lichens.

Those groups are still called cryptogams sometimes, but this name is the only thing reminding of Linnaeus’ 24th class. New pieces of evidence have meant considerable changes to the systematic biology. Fungi and lichens are now referred to a realm of their own, Fungi. The algae have been shown to consist of several very different groups belonging to a new realm, the Protista. Ferns and mosses are still considered to belong to the plants, Plantae, together with flowering plants and conifers.

When comparing the sexual system of Linnaeus with a modern classification system, large differences are found. The group of organisms treated in the sexual system is today divided into 25 groups, divisions. Of these the flowering plants and conifers are divided into 5 divisions while the cryptogams are divided into 20 very heterogeneous divisions. In other words, there was greater variation within the 24th class of Linnaeus’ system than he could ever imagine.