Peloria – a monster
Common toadflax, Linaria vulgaris, has a two-lipped flower with a spur. It has four stamens, of which two are longer than the other two. It was hence placed in the class Didynamia in the sexual system. The Peloria flower on the other hand has five spurs and five stamens of equal length, and was placed in a different class, the Pentandria.
How could the stamens differ so much between two otherwise very similar plants? Linnaeus at last suggested that Peloria was a hybrid between common toadflax and some other, unknown, plant. If the seeds of this hybrid could germinate and grow into new Peloria-plants one would have had to draw the conclusion that new species could originate in nature.
Today we know that Peloria is a form of common toadflax, which every now and then appears by spontaneous mutation. Meeting Peloria Linnaeus had to consider that a species might not be as stable as he had thought.
Linnaeus’ thoughts about speciation through hybridisation were not erroneous; on the contrary he was much before his time in thinking like this. Speciation can happen when a hybrid goes through a duplication of its genetic material. With a double amount of genetic material, neither the hybrid nor its progeny can interbreed with any of the parental species. They are isolated and a new species has sprung up.
Spur: A spur is a conical part of a petal, often containing nectar. A visiting insect has to stick its proboscis into the spur to suck the nectar.
Mutation: A mutation is an instantaneous change in the genetic material. This can happen in many ways, for example under the influence of the strong UV-light of the sun. Some such changes are invisible while others can bee seen clearly. An example of a sometimes occurring mutation is the white flowered form of the otherwise blue flowered liverleaf, where the ability to produce blue flowers has been affected.