If a dried specimen of an extinct plant species still has seeds in a herbarium, is the plant really extinct? A global team of scientists toyed with that question. To arrive at the answer, they made a survey of all extinct plants in herbariums that (may) still possess germinating seeds.
When is a speciesextinct?
A plant or animal is extinct when the species ceases to exist by the death of the last specimen. But when exactly is a plant extinct? Is a plant species extinct if there are still dried specimens with seeds? You can ask that question. Also the question of how many such cases there actually are. Led by Giulia Albani Rocchetti togehter with prof. Thomas Abeli, both of the University of Roma Tre, a team of researchers started this investigation, including biologist Jan Wieringa and collection manager Roxali Bijmoer of Naturalis Biodiversity Center.
From a list of 361 extinct plant species, specimens with fruits containing ripe seeds were searched in 61 herbaria, including Naturalis' collection. Of 161 species (45%), one or more specimens with seeds were found. Thus, there are at least 161 species for which seeds do still exist and can potentially be revived. Very little is usually known about these species themselves; they were already rare and were often collected only once or twice in the distant past. Such as Achyranthes mangarevica, a distant relative of spinach and beet known only from a cliff on an island in the Pacific, and Lepidium remyi, a relative of garden cress that grew on an island of Hawaii and was last collected 170 years ago.
To estimate whether the seeds might still be able to germinate, we looked at the germination rates of related species that are known to do so. This eliminated a number of candidates. Some seeds in herbaria were collected a long time ago; the oldest ones usually do not even have a known date. But there are also some from the last few decades. Based on the age of the seeds and an estimate of how quickly they lose their germination, a score was calculated for each species. Based on that score, a top-50 of species with the highest chance of being "revived" again was compiled. The species could potentially be revived by sowing the seeds of the herbarium specimens or by making a tissue culture of them.
Yet sowing the seeds of these plants will not be so simple. Not only are most of them very old, but herbaria are not set up to keep seeds alive. Indeed, most herbaria take all sorts of measures to kill unwanted organisms, such as museum beetles that prey on the dried flowers. This protection from predation has been done at Dutch herbaria in the past by poisoning the plants with mercury, and in recent decades by freezing the material. Tropical seeds in particular will take low temperatures very badly, and many of the top-50 species are tropical. Possibly these conservation measures have actually killed the last chance of reviving these extinct species. But who knows what new techniques science still has in store.