Stirling, Scotland. Two foreign plant species formed a hybrid that overcame infertility, a rare example of a new species that has originated in the wild in the last 150 years.

The new species of monkeyflower (Mimulus peregrinus) was discovered on the bank of a stream in Scotland. Thousands of wild species and some crops that are thought to have originated in this way, yet this type of species formation is rare in recent history.




British Monkey Flowers

A. The North and South American parents (Mimulus guttatus, the yellow monkey flower).

B. (Mimulus luteus, blood-drop emlets.

C. The sterile hybrid.

D. The new species.

Scale bar = 1cm.The ancestors of the new plant were brought from the Americas as botanical curiosities in the 1800s and were quickly adopted by Victorian gardeners. Soon after their arrival, they escaped the confines of British gardens and can now be found growing in the wild, along the banks of rivers and streams.

Reproduction between these species produces hybrids that are now widespread in Britain. Yet, genetic differences between the two parents mean that the hybrids are infertile and cannot go beyond the first generation.



Mimulus peregrinus, the new species of monkeyflower.

All photos courtesy of Mario Vallejo-Marin.Mario Vallejo-Marin, a plant evolutionary biologist at the University of Stirling, documented the first examples of hybrid monkey flowers that have overcome these genetic barriers and show fully restored fertility. This fertile hybrid derived from immigrant parents represents a new species, native to Scotland. The species name, Mimulus peregrinus, translates as the wanderer and is described in the journal PhytoKeys.

The two American monkey flowers are unable to produce fertile hybrids due to differences in the amount of DNA present in each species, the equivalent of getting a sterile mule from crossing a horse and a donkey.

However, in rare cases, duplication of the entire hybrid DNA, known as polyploidization, can balance the amount of DNA and restore fertility. "Our studies suggest that this is what has happened here," said Vallejo-Marin.

The discovery will help scientists to understand how new species form. It is thought that many existing plant species including crops such as wheat, cotton and tobacco may have originated in a similar way, but finding examples of this process in action is rare.

"This is an exciting opportunity to study evolution as it happens", said Vallejo Marin. "We do not yet know how common the new species is or how well it will fare, so the next step will be to find out its distribution and whether its ecological characteristics allow it to colonise environments that cannot be currently exploited by its parents."