by Wesley M. Knapp, North Carolina Natural Heritage Program

I’m an optimist at heart, which makes the topic of extinction a sobering contrast to my personality. Yet, extinct plants have captured my imagination for some time. This interest started right out of undergrad, when I landed my “Dream Job” as a field botanist with the Maryland Natural Heritage Program. It was an intimidating prospect for me, a 21-year old without a lot of field botany experience, as I was supposed to know enough to wonder about and discover and document rare plant species. I studied the Rare plants of Maryland tirelessly to better familiarize myself with the diversity of plant life that occurred on Maryland’s Eastern Shore. One night while studying the Rare plants list, I came to Nuttall’s Micranthemum (Micranthemum micranthemoides). This species is responsible for my interest in extinct plants.

Nuttall’s Micranthemum is the opposite of charismatic megafauna. It is a diminutive and rather non-descript mud flat species of fresh-intertidal streams. It was found from the Hudson River in New York through New Jersey, eastern Pennsylvania, Delaware, Maryland, and tidewater Virginia. It is the only plant in the entirety of the Maryland Flora considered globally extinct. I had not realized that extinct plants were found in places like Maryland, assuming they were in far off exotic places like the Amazon or the tropics. I took it as a challenge to learn everything I could about this plant and to rediscover it. I mean, it had to be out there somewhere, as there are seemingly hundreds of linear miles of habitat for this species on the Eastern Shore alone.

Last seen in 1941

Well (spoiler alert!), I did not find it! It was last collected by Fernald & Long on 13 September 1941. It was apparently not uncommon at this location, as I have seen numerous duplicate locations from the same date and location at different herbaria. The story goes that Fernald & Long were out collecting, in part, to find and document more of this plant. They succeeded, and this is apparently the last time it was ever observed by man.

When I would attend conferences or talk with other botanists, I would often ask, “What extinct plants are known from your State?” I was surprised to discover most botanists had no idea. For a long time I kept an unofficial list of all the extinct plants I heard of or ran across in floras or manuals, but I never officially worked on an extinct plants project, as I always assumed this work had to have been completed.

In 2015 I saw Reed Noss present a paper at the Ecological Society of America in which he detailed how many plants and animals were expected to go extinct in Florida over the next 100 years (based on sea-level rise, population growth, etc.). It was only then I realized we did not have an estimate of how many plants were already extinct. I reached out to a large number of experts from across the country to determine if I’d missed some critical piece of literature that already answered the question and invited them to collaborate if the work hadn’t been done. It was exciting, if not a bit intimidating, that so many experts thought the work needed to happen, and I was the one to lead it.

Fast forward to 2020, and the project has finally been completed and the journal Conservation Biology has accepted the work. The results are sobering and document more extinct plants from the continental United States and Canada than ever before. We documented 65 extinct taxa (51 species and 14 varieties and subspecies) from 33 families and 49 genera.

In the Southeast, 80% of extinct plants were not forest plants

And guess what? In the SGI region, 80% of the extinct plants occupied some type of non-forested habitat. Determining the cause of any extinction event can be difficult to definitively know, unless that species was a single-site global endemic whose site was destroyed. Even the small and apparently widespread Nuttall’s Micranthemum’s cause for extinction is unknown, but it was likely a death by a thousand cuts (habitat alteration, shoreline stabilization, wakes of passing boats, saltwater intrusion, invasive species, etc.), but an unknown pathogen could have also been a possible cause.

Though the total number of extinction events is much higher than any previous estimate, we are positive it is a gross underestimation of the actual extinction events of the region. An untold number of species went extinct before they were ever documented by man. Two facts allude to this. First, there are far more extinction events known from the western United States than the east. This is likely, in part, a result of botanical survey before widespread Euroamerican settlement. So many areas of the east--particularly open, treeless habitats that were easy to settle and are known to harbor narrow endemic species--were destroyed before botanical exploration. Secondly, the known extinction events in New England outnumber Florida. New England is a special place, but botanically speaking, it is not nearly as diverse as Florida, which is the epicenter of the Coastal Plain Biodiversity Hot Spot with hundreds of endemic plants.

A final hint to the amount of botanical diversity never documented is that four species have been described since 1995, which are known only from old herbarium specimens. Put simply, these four species were never recognized as distinct species before they went extinct.  They were collected, turned into specimens, and only decades later recognized as distinct species.

Rediscovering the last plant of its kind on earth

Interestingly, seven of the 65 extinct plant taxa we recently reported are considered Extinct in the Wild (EW) meaning they can be found in Botanical Gardens. Shockingly, most of these seven were not recognized as such before this study and only one of these was a collection made to explicitly prevent an extinction event!  I discovered these botanical collections while researching extinct plants through the Botanical Gardens Conservation International (BGCI) database.

One extinct plant, the St. Clair Hawthorn (Crataegus fecunda) was reported to be at the Morton Arboretum. I was very skeptical at first, as there are numerous errors in the BGCI database that resulted in hours of identification crosschecking, and Hawthorns are notoriously difficult to identify. It took numerous emails between myself and two more experts, trading photos from different times of year to confirm the identification.

It is the last known St. Clair Hawthorn plant on earth.

I got goosebumps when Ron Lance confirmed the identification. This discovery made me realize the critical role Botanical Gardens have in preventing extinction. We need to assist gardens in prioritizing the rarest plants for ex situ conservation (i.e. seed banking and living collections in conservation gardens).

Trends and implications for biodiversity conservation

The only EW plant collected to prevent an extinction event is the Franciscan Manzanita (Arctostaphylos franciscana). This species was believed extinct before its rediscovery in 2007. Unfortunately, the Franciscan Manzanita was found in the path of a “shovel ready” road construction/upgrade project leading to the Golden Gate Bridge. The plant’s (re-?)extinction was imminent. Conservation groups sprung to action, putting the species into conservation gardens and moving the living plants to a nearby site where they would be protected. We consider this species EW, as there are no naturally occurring populations. Though it is unfortunate this species is EW, it is much better than having no populations remaining. We’d best get used to it, as this will likely be an increasing trend in plant species conservation over the next 100 years. 

Another surprise was the number of extinction events of single-site global endemics. These are species known from a single small site or extremely narrow geographic distribution. Our data show that 64% of the extinct plants were single-site global endemics. This has major implications for biodiversity conservation. Lots of conservation groups focus on large scale focal areas, which is critical in maintaining ecosystems and keeping common species common. Small scale site protection needs to be prioritized if biodiversity conservation is the goal. These two goals are not necessarily mutually exclusive, and in many cases could probably be accomplished in tandem, as small sites with unique biodiversity can be anchors of larger ecological preserves, and protection of these sites is critical to prevent extinction.

Rediscovering “extinct” species: unlikely but not impossible

Determining that a species is extinct is nearly impossible and is mostly a sliding scale of confidence. That is why I prefer to say, “presumably extinct.” There is always the chance a species believed extinct is over the next knoll or up the next creek, but each of the 65 plants listed as extinct in our paper has been searched for and no individuals are known. I hope the botanical community takes it as a challenge to go looking for these species with renewed interest, and I hope that each of these 65 extinct plants is rediscovered. Any resulting rediscovery would immediately become a global conservation priority. Extinct species could still be out there, but the likelihood is low.

The Baja Oatgrass (Sphenopholis interrupta ssp. californica) was believed to be a globally extinct species known only from Mexico, having been collected twice in 1890. Just this year (April 2020) this plant was rediscovered in California by Jessie Vinje and Margie Mulligan. A rediscovery of a presumably extinct species in a country to which it had never been attributed! The Wollemi Pine is probably the greatest story of rediscovery. This species was only known from the fossil record of the Cretaceous era (145 -- 66 million years ago), until it was discovered by David Nobel in Australia in 1994. Rediscovery stories like this are very rare and astonishing events that give us hope.

Do I expect the extinct plants of the continental United States to be rediscovered? No. Please, plant lovers, prove me wrong.