How the Botanic Gardens can help save plant species on the brink of extinction

The last individual of the Portuguese coastal plant species Armeria arcuata, extinct in the wild, was thought to be growing at the Utrecht University Botanic Gardens. But when researchers compared the DNA of this plant with DNA of Armeria arcuata collected in the mid-19^th century, they found substantial differences. The conclusion: Armeria arcuata is indeed extinct. Anastasia Stefanaki, curator of the rock garden at the Botanic Gardens: “Thanks to our collections, the true identity of the species was clarified. And while in this case the ending is unfortunate, next time it could be the right species.”

The small coastal flowering plant with the name Armeria arcuata was only collected once, in 1848. Despite repeated efforts to find it, it has not been seen in the wild since. As a result, it was believed to be extinct. However, in 1984, the Botanic Gardens received a plant thought to be Armeria arcuata from a grower specialized in rare alpine plants in De Bilt. Descendants of this plant are still growing in the rock garden of the Botanic Gardens these days.

Reintroduction

Potentially, the plants in the Botanic Gardens could have opened up the possibility of reintroducing Armeria arcuata in the wild. That prompted Thomas Abeli, conservation biologist at the University of Pavia, to reach out to the Botanic Gardens to ask for plant material of one of the presumed Armeria arcuata specimens. Abeli and his colleagues set out to compare the DNA of the plant in Utrecht with that of the original specimens collected in 1848, which had been dried and stored in the Herbarium of Geneva. They also gathered material from other Armeria species housed in various botanic gardens and herbaria.

Stefanaki: “Extracting useful DNA from old herbarium specimens used to be very difficult, but it has become much easier, opening up exciting opportunities for research like this.”

Difficult to identify

Many plants, and often those of the genus Armeria in particular, are challenging to identify, according to Stefanaki. “Just from morphology, it is sometimes really hard to tell species apart, even for specialists. DNA is a useful complementary tool in such cases. And in plants, defining what exactly constitutes a species is tricky. The most common definition of a species is that organisms can reproduce and produce fertile offspring. But many plant species can hybridize with related species and still produce fertile offspring.”

For plants to be reintroduced into the wild, the correct identification is essential.

DNA comparison

Most plant-DNA is located in the nucleus of the cells, but DNA can also be found in the chloroplasts, the components in plant cells where photosynthesis takes place. When both the nuclear DNA and the chloroplast DNA of the supposed Armeria arcuata plant from Utrecht were analysed, it turned out that the nuclear DNA suggested a relationship to one species of Armeria, while the chloroplast DNA suggested a relationship to another. Stefanaki: “This shows that the specimen from the Botanic Gardens is probably a hybrid between two different Armeria species.”

The DNA analysis also revealed substantial differences between the plant growing in the Botanic Gardens and the Armeria arcuata specimens that were collected in 1848, confirming that Armeria arcuata is indeed extinct.

Interestingly, analysis of the DNA of Armeria arcuata revealed that the plant may also be a hybrid itself. “With the information we now have, we cannot be sure whether Armeria arcuata at the time of collection was an established, stable hybrid, which would make it a distinct species, or a relatively new, short lived hybrid,”  Stefanaki points out.

Role of botanic gardens

Even though in this particular case the outcome was unfortunate for the survival of the species, the story shows how botanic gardens can be a place where threatened plants, or even species that are extinct in the wild, can be maintained to be potentially reintroduced into the wild. For this purpose, botanic gardens do actively propagate and share specimens of threatened plant species.

This could also be one of those cases where human impact led, sadly, to the extinction of a plant species.

Moreover, this case shows how botanic gardens make research on plant conservation possible. “The Utrecht University Botanic Gardens are a member of the Botanic Gardens Conservation International (BGCI),” Stefanaki explains. “So we upload all our collections to their online database. People interested in plant conservation, such as the researchers that reached out to us in this case, can search the database for specific plants that they are interested in. They can then request material to do their analyses.”

“For plants to be reintroduced into the wild, the correct identification is essential,” Stefanaki says. “This example shows that DNA is a powerful tool that can help clarify the ambiguous identity of endangered plant species. But using DNA to help solve specific issues in plant identification, as we did here, is demanding and time consuming. We can do it when it is necessary to answer crucial research questions, as in the case of this putatively extinct species, but we do not do it for our entire collection.”

Coastal plants

The extinct species Armeria arcuata was a coastal plant, which, according to Stefanaki, may not be a coincidence. “Many plants that grow in Mediterranean coastal areas are under threat,” she explains. “That is because people are also drawn to the coast, and these areas experience intense human disturbance. This could also be one of those cases where human impact led, sadly, to the extinction of a plant species.”