The world’s rarest plant?

We’ll probably never see this plant again. Image from Wood (2012)

Many of the rarest and most endangered species we know of are plants. The sad story of Hibiscedelphus woodii, which I’ve only just read about, is not atypical. Of the 4 last known specimens, on a cliff in Hawaii,

three individuals of H. woodii were apparently crushed by a large fallen boulder and died between 1995 and 1998. on 17 August 2011, the last remaining H. woodii was observed dead. [zotpressInText  item=”X8HWMKBN”]

The unfortunate (but appropriate) choice of this as a endangered species at a recent event for the Society of Biology, prompted me to dig out the following, which I wrote in 2009 to answer the question “What is the world’s rarest plant”:aEveryone attending the event at the House of Commons was asked to vote for an endangered species they would choose to save, from a list of 6. Perhaps predictably, it ended up as a toss-up between the giant panda and the Spoon-billed Sandpiper (the panda eventually won this “sudden-death” shootout). The poor Arrow cichlid only got 8 votes, which surprised me in an audience of biologists, given that cichlid fishes are often seen as second only to Darwin’s finches in terms of classic examples of evolution in action. [zotpressInText  item=”2HMRGRR2″]

The unfortunately named “bastard gumwood”, Commidendrum rotundifolium, of which only a single specimen existed in 2009 (photo courtesy of Phil Lambdon)

As habitats change, it’s likely that several – probably unknown – plant species will consist of one remaining individual. You can’t get much rarer than that! It’s reasonable to say this because many species, mostly long-lived trees or shrubs, were previously known from one wild plant. However, once discovered, these incredibly rare species are often conserved through propagating seeds, cuttings, etc. and so their numbers (at least in cultivation) increase somewhat. Examples include Dendroseris neriifolia on Robinson Crusoe island, the Cafe Marron (Ramosmania rodriguesii) on Rodrigues, and the Three Kings Vine (Tecomanthe speciosa) on a New Zealand island. You can look at the IUCN red list which, as of 2009, describes 28 plants as actually extinct in the wild. Many of these are only just hanging on in cultivation. I’d highlight the Wood’s Cycad (Encephalartos woodii: all remaining individuals are male clones and no females exist), Kokia cookei from Hawaii (all are grafts from one branch, itself grafted from a single rediscovered tree, since accidentally burnt down), and the unfortunately-named Bastard Gumwood from St. Helena (Commidendrum rotundifolium: I’m told it’s now reduced to one pure-bred tree). That these rare endemics are mostly from remote islands shows the processes of evolution and speciation at work.

Of course, it’s not just plants. Given the current rate of extinction, any one time, there are bound to be many of species of life on earth that, whilst on their way to extinction, have been reduced to a single individual. Among animals, Lonesome Georgebadmittedly Lonesome George was “only” a subspecies of giant tortoise, not a full species in its own right, and Martha spring to mind; I’m sure there are others. However, the category of “so-rare-that-only-one-remains” seems to be dominated by trees and shrubs. I suspect that’s a case of selection bias. Unlike say, insects, a single woody plant can hold on for a relatively long time: long enough, at any rate, to be discovered and catalogued, before its unfortunate demise.

My old plant science lecturers, Mark Large and Quentin Cronk, helped me answer the original question, but the Bastard Gumwood detail came from Phil Lambdon of Kew, who knows a lot about the botany of the south Atlantic island of St. Helena, and of oceanic islands in general. In fact, nearly all the examples I’ve listedcThe passenger pigeon is a spectacular exception to the rule of rare species existing largely on islands. Although it’s a bit old now,  I’d thoroughly recommend reading chapter 88 of David Quammen’s “The Song of the Dodo” for a eloquent background on this extinction. It makes me emotional every time I read it. are endemic species that have evolved on isolated oceanic islands. Of course, remote islands are well known for unique flora and fauna – the outcome of the processes of evolution and speciation, and one of the things that caused Darwin to come up with his theory. As to the current plight of these fascinating natural laboratories of evolution, I think that the email that Phil sent me in November 2009 is telling:

Dear Yan

St. Helena has approximately 45 endemics, at least 15 of which are in a very precarious position and 6 of these have fewer than 10 plants in the wild. The most extreme case is that of Commidendrum rotundifolium, which has the rather inelegant local name of bastard gumwood. This species is extinct in the wild, and is now possibly reduced to a single individual in cultivation.

The single remaining bastard gumwood in 2009, behind a rickety shed on St Helena (image courtesy of Phil Lambdon)

The bastard gumwood is one of several “tree daisies” to have evolved on the island, four of which are characterized by their gummy sap. Although very few historical records exist, it was probably adapted to the most extreme arid conditions of all the group, occuring on the desert-like, rocky slopes which occur at lower altitudes. Its decline was probably attributable to the ravages of introduced goats and felling for firewood. By the late 1900s, it was all but extinct and given up for lost. In the 1980s, two local “Saints” Stedson Stroud and George Benjamin, (both now considered to be the legends of St. Helena conservation), refound a single tree growing on a remote cliff whilst out searching for wild bees. The plant died a few years later, but cuttings were taken into cultivation and grown successfully. Unfortunately through lack of expertise, the cultivated stock dwindled, and is now reduced to a single decrepit old plant, propped-up by stakes and unglamorously situated alongside a rickety shed. Although renewed attempts at cultivation have taken place, the original stock was innocently grown in a seed orchard alongside the other endangered Commidendrum species. Seed was collected and approximately 90 plants reared, but I am reliably informed by the new Horticultural Officer, Lourens Malan, that the vast majority, if not all, of the plants which are currently being grown appear to be hybrids. There is a high likelihood that we are left with just the ageing parent. A last ditch rearguard action to save the species is due to take place over the next few months, when the plants are due to flower again.

Best wishes

Phil

Although disappointingly, it didn’t work for the Hawaiian Hibiscedelphus, propagating plants from cuttings or selfed seed has saved a number of plants from the brink (although I assume problems with genetic diversity are likely to remain). As well as the three examples I mentioned in my original reply, Pennantia baylisiana is another plant I have recently come across which was down to a single tree, but where seedlings have now been propagated for reintroduction. Indeed, such is the popularity of owning iconic rare plants that some critically endangered plants are now commonly cultivated by gardeners all over the world – you only have to think of the Wollemi pine which can be ordered online from a number of outlets! It’s an interesting illustration of the social context and economics of modern conservation. Perhaps the bastard gumwood will live or die on the basis of its name and marketability as a symbol of conservation? That’s an area where you might expect plants to be outgunned by the cute and fluffy brigade, and one of the reasons that I would argue to optimise for habitat conservation (although that doesn’t rule out using iconic species to do so).

The highs and lows of conserving rare plant species make it impossible to give a fixed answer to the question at the heart of this post. The title of “world’s rarest plant” changes surprisingly quickly from year-to-year, as some lone individuals narrowly escape extinction by a successful conservation strategy, or get wiped out by a series of all too common accidents. Although accidents may have the upper hand, it does give me an excuse for ending the post on a positive note. The updated status on the bastard gumwood (as of 2010 and 2012) seems more promising. Indeed, there even seems to be a “Bastard Gumwood Recovery Officer”, a job title of which I’m rather jealous.

If I find out anything more about conservation progress on the bastard gumwood, I’ll post it here.

REFERENCES

Notes   [ + ]

a. Everyone attending the event at the House of Commons was asked to vote for an endangered species they would choose to save, from a list of 6. Perhaps predictably, it ended up as a toss-up between the giant panda and the Spoon-billed Sandpiper (the panda eventually won this “sudden-death” shootout). The poor Arrow cichlid only got 8 votes, which surprised me in an audience of biologists, given that cichlid fishes are often seen as second only to Darwin’s finches in terms of classic examples of evolution in action. [zotpressInText  item=”2HMRGRR2″]
b. admittedly Lonesome George was “only” a subspecies of giant tortoise, not a full species in its own right
c. The passenger pigeon is a spectacular exception to the rule of rare species existing largely on islands. Although it’s a bit old now,  I’d thoroughly recommend reading chapter 88 of David Quammen’s “The Song of the Dodo” for a eloquent background on this extinction. It makes me emotional every time I read it.

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