Tag Archives: botany

Of otters and scurvygrass

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A dense patch of scurvygrass (Cochlearia officinalis agg.) in an area much frequented by otters based on the clear trails, spraint and crushed mollusc shells.

On a sunny February weekend I made a trip out to Bere Island (Oiléan Béarra), a short ferry-ride off the southwestern tip of Ireland, to investigate a peculiar botanical phenomenon. An old friend had called on me recently and enquired what the connection was between otters and scurvygrass (Cochlearia officinalis L.*). I confessed to knowing nothing about it and was slightly sceptical, but he was adamant that there was such an association, and wanted to show me in person. Any excuse for a field trip is welcomed so off I went.

Once there on the ground there’s no doubt about it. The otter haul-outs are very obvious, and invariably marked with scurvygrass. The plant does grow elsewhere, unsurprisingly, but never in such densities and with such luxuriant foliage as where they occur alongside otter signs. Whatever the otters are doing, the scurvygrass is enjoying it. A representative sample of rocky outcrops suggests that if you spot a patch of scurvygrass it’s clear indication that once you get up close there will be matching evidence of otters. Neighbouring outcrops lacking the plant are also devoid of otter signs.

It’s not only at the shoreline where otters leave the sea, and where their spraint or the remnants of smashed shells indicates favoured spots to hang out. Their tracks continue inland. Often after coming onshore the track leads directly to a freshwater pool, suggesting that they like to wash the salt water off their fur, then out the other side. They then wend their way through the grass and heather, apparently choosing to cross the island on foot rather than swim their way round.

This is where it gets even more interesting: in the midst of these fields, scurvygrass is only found on the otter trails. Elsewhere the sward is higher and there is no sign of the plant. Otters are clearly carrying scurvygrass inland and encouraging it to grow in places where it otherwise would not. This effect is only seen in fields which don’t contain livestock; cows and sheep have a tendency to share the same trails with otters and perhaps browse or beat down the scurvygrass. But on the old military firing range, where otters have the land to themselves, every one of their trails is peppered with patches of the plant.

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An inland otter track through a field with a dense grass sward. Scurvygrass can only be found along this trail.

On returning to the office I consulted the usual books to see whether I could find any record of this particular association, and drew a blank. Web searches, whether in the scientific literature or the internet at large, have also come up with nothing. So what is going on? I have a few hypotheses:

  1. It’s a coincidence. Any ecologist has to keep the null hypothesis in the back of their minds. Maybe this is pure chance, or else some unknown independent environmental factor dictates the combined presence of otters and scurvygrass. I haven’t done a randomised sampling design to demonstrate a statistical association, but often the evidence of your eyes is enough to tell you that there’s no need.
  2. Otter disturbance. Scurvygrass thrives in patches with frequent disturbance, and the constant to-and-fro of otters might open up denser vegetation in such a way that they allow it to enter. Perhaps scurvygrass is more tolerant of this kind of disturbance than other plants.
  3. Dispersal by otters. The seeds of scurvygrass don’t look like they are adapted for sticking to the sides of animals, which would be one mechanism. Do otters eat scurvygrass, and thereby carry the seeds with them, defacating them in freshly-disturbed areas that aid its germination? This is currently my favoured explanation, but I don’t know enough about the diet of otters to be sure.
  4. Saline environments. Perhaps all the salt water clinging to the fur of otters changes the soil at their haul-outs and along their trails, favouring the growth of a halophyte such as scurvygrass. This is possible, but not entirely plausible given the presence of patches quite a way inland and even after they’ve taken a freshwater bath. Soil samples might resolve this. There are also no other halophytes which show the same pattern.
  5. Otters go where the scurvygrass is. Maybe they like the feel of it on their paws? It’s unlikely to be that they’re feeding on it, otherwise you would expect to see less scurvygrass in the places they use most frequently, while the opposite appears to be true.

Have I missed anything? Is this a known phenomenon that my friend has independently discovered? I’d be interested to hear from anyone who knows more about this in the comments. For now it’s only a small mystery, but also an intriguing natural history observation, and a reminder that people who walk outdoors and watch the world around them carefully often spot patterns that professional ecologists in their offices would never find.

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Credit to Bere Island resident Maurice Neligan for spotting this interesting pattern.


* This is as close as I can get to an exact species identification. Stace notes (in the 3rd edition; I don’t have the latest one just yet) that C. officinalis is highly variable, an aggregate of several likely species, and also freely hybridises with C. anglica and C. danica, especially in Ireland.

UPDATES!

As ever, Twitter provides a wealth of insights from other botanists. Here are the pick of the suggestions:

The first can be summarised as ‘disturbance + fertiliser’, the second with the twist of extra salinity, which might not be important given observations elsewhere. But scurvygrass isn’t only found where spraint occurs. It’s also along trails, some of which are quite steep, and any spraint is likely to roll or blow away pretty quickly. Otters may be marking trails with urine which could have a similar effect. Scurvygrass is also found right at the point at which otters emerge from the sea. I can’t help thinking that there must be a dispersal element to the story as well. This seems to be supported by another sighting of scurvygrass associated with birds:

There’s only one thing for it — we need to do some experiments! This may not be the most important project on my list but it makes for an enjoyable distraction.

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Field notes from Mexico 6 — a botanist in the museum

On my last day in Mexico, my hosts kindly took me to see the National Museum of Anthropology in Mexico City. First of all — wow. It’s absolutely spectacular, and if you have even the slightest interest in human history, culture and archaeology then you should go. Much like the British Museum* in London, you simply can’t take in the whole place in a single day. In fact, you would struggle to do so in a week.

In a single afternoon I was only really able to take in two archaeological sections: the Mexica empire, and the civilisations of the Pacific coast. The former were characterised by a militaristic state, the latter by their complex cultures and fine crafts. In fact, I was even more focussed, as I was specifically looking for evidence of botanically-inspired features among the artefacts, and I found plenty.

Many of them, interestingly, were related to cacti. This surprised me. Although Central America is the cradle of cactus diversity, and they are the most distinctive feature of Mexican dry vegetation, they are also relatively unimportant as crops and a minor component of most systems. Evidently they were considered worthy of carving into stone though.

In the section on the Mexica, rulers of the Aztec Empire, there is an altar with an Opuntia (prickly pear) clearly depicted on the rear face. This distinctive cactus provides a useful resource: its pads, once cleaned of the spiny glochids**, are cooked as a vegetable, known today as nopales, a word which derives directly from the Nahuatl as spoken by the Aztecs. Likewise the fruit, tuna, is still harvested and eaten widely in Mexico. The name Opuntia itself, however, is from the reference by Theophrastus to a plant in the classical Greek city of Opus which could grow from a leaf that was stuck in the ground. He wasn’t talking about a cactus though, because although they are now invasive in some parts of the Mediterranean, they definitely hadn’t arrived there in 300 B.C.

 

Opuntia isn’t solely used for food though; one of its more surprising appearances was in a reconstruction of a burial chamber from La Cueva de la Candelaria, on the border between the modern states of Hidalgo and Durango, which was occupied around 1100–1300 AD. The bodies each rest upon a layer of Opuntia pads. It hardly seems like comfort — no-one would do that if they were alive — perhaps these were provisions for the journey beyond?

Other cacti have more entertaining functions, such as peyote (Lophophora williamsii), a favourite hallucinogen for ritual and recreational use. It appears as a design on a large pot, and also in my favourite piece in the museum, a ring of revellers surrounding a shaman who is clearly holding a cactus in his hand. Both are from the Tumbas de Tiro tradition of West Mexico (200–600 AD).

RIMG2623To finish off the cacti, how about this metre-tall carved columnar cactus, probably from the genus Cereus? I definitely coveted this for a corner of my living room. It’s thought to be a boundary marker between two territories, and has the face of a legendary Mexica leader carved into its base. What interests me is that this kind of cactus isn’t present in that area, at least not in the modern world. Was it chosen because it was a feature of the landscape back then, or alternatively because it would stand out as unusual?

Other plants have important cultural associations. I’ve mentioned Agave before on this trip, particularly with reference to the manufacture of the alcoholic beverage pulque. I learnt much more in the museum though. Pulque had its own god, Ome Tochtli, which translates as ‘Two Rabbit’. Adults were only permitted one drink of pulque in any sitting (size not specified), and drunkenness was heavily frowned upon, lest one lose control and fall under the violent spell of Cenzon Totochtin, or ‘Four Hundred Rabbits’ (which, wonderfully, is the name of a popular brand of mezcal). So remember kids, two rabbits good, four hundred rabbits bad.

RIMG2635Another impressive piece of Mexica sculpture was this calabaza (Cucurbita moschata), a relative of the modern pumpkin. This magnificent piece was the size of… well, a ripe pumpkin. Alongside maize, which appeared in countless exhibits, beans and chilli, this was one of the staple foods of the peoples of central Mexico.

Not all the exhibits were carved in stone. One of the most important documents held by the museum is the Botorini Codex, a long pictographic account painted on fig bark by an Aztec artist around 1530–1541, so not long after the Spanish arrived. It tells the legend of how the Aztec arrived in the Valley of Mexico after leaving their original home of Aztlan. They decided to settle there due to the abundance of resources, but their first action was, of course, to cut down the trees. This is a useful reminder that tropical deforestation is by no means a new phenomenon, even if its intensity has increased in the modern world. One puzzling mystery though: why does the tree have arms?

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A section from the Botorini Codex illustrating the clearance of forests in the Valley of Mexico following the arrival of the ancestors of the Aztec.

Finally, I’ll finish with another Mexica carving. On first inspection it looks like a bird sitting in a stylised flowering tree. But look more closely and you’ll see that the bird is eating some kind of caterpillar. In other words, it’s an archaeological representation of a tritrophic interaction! Perhaps they would have been unsurprised by findings of ecologists in Panama 500 years later that birds protect trees from herbivory.

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Bird eats caterpillar eats tree. Tritrophic interactions in archaeology!


* Which is an order of magnitude larger again, thanks largely to the pillaging of cultures around the world in the name of empire, such as in the notorious case of the Elgin Marbles.

** Bristly patches of spines on some cacti, which often have barbs and detach when touched. I recommend a bar of soap to remove them. Then throw away the bar of soap before anyone else uses it by accident.

Field notes from Mexico 5 – ghost plants

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Monotropa uniflora in the understorey of an Abies religiosa forest, El Chico National Park, Hidalgo, Mexico. Thanks to Sarah Pierce for the ID.

On numerous occasions on our trip through the coniferous forests of Mexico on the #PinaceaeGo project, we’ve encountered a ghostly pale plant on the forest floor. Depending on where in the world you’re from, it might look very familiar; or totally unlike anything you’ve ever seen before. That in itself is part of the mystery surrounding this plant.

Monotropa uniflora is variously known as the ghost plant, corpse plant, or Indian Pipe. As its appearance suggests, it is parasitic, and does not contain any chlorophyll of its own for photosynthesis. Unlike most parasitic plants, however, it doesn’t obtain its energy from other plants. Instead, it is an unusual example of a mycoheterotroph— it steals sugars from mycorrhizal fungi in the soil which are themselves symbiotic partners of trees. In other words, the trees choose to associate with the fungi, providing them with sugars in return for soil nutrients. Monotropa hijacks this arrangement and takes from the mycorrhizae while offering nothing in return.

This indirect theft is what allows it to survive even in dense, dark forests, and to be associated with a range of forest types. While most parasitic plants target particular plant species, M. uniflora is highly specialised on a few species of mycorrhizal fungi from the Russulaceae. All these features set mycoheterotrophs apart from more common parasitic plants such as dodder (Cuscuta spp.) or broomrapes (from my favourite plant family, the Orobanchaceae**), which are direct parasites on other plants.

Confusion over the taxonomy of Monotropa has been long-standing. Prior to Linnaeus, a related species Monotropa hipopitys was actually included in the genus Orobanche. Early botanists must have thought that parasitism ranked as a higher criterion for organising plants than flower traits. For a while it had its own family, the Monotropaceae, but it is now incorporated into the Ericaceae, along with heathers and Rhododendron, which superficially look nothing like it.

Another of its bizarre features is what biogeographers refer to as a disjunct distribution. It occurs in all sorts of places worldwide, in Russia, North and South America, but with large gaps between them. Genetic evidence suggests that these are distinctive, but not enough to call them different species. How did they get to such widespread locations? Was it through their dust-like seeds, or linkages in previous climates, or human transportation? Even where it is found, it’s never very common, and appears only in certain seasons.

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Global distribution of Monotropoideae (including Monotropa uniflora) from Kathleen Kron’s Ericaceae site.

It’s not often that one can come across the same distinctive species in so many places around the world. How did a species of heather come to evolve into a fungal parasite, to develop such a strange form, and to spread itself quite so far? Wherever you find it, it’s always going to be special and mysterious.


* Here’s a pretty old review of this group of plants from 1994. If another has been published since then I’m unaware of it, and suggests that there might be scope for an update.

** One day I hope to retire to a herbarium and prepare a full review of the Orobanchaceae, so long as no-one else gets there first. I collect them on sight, wherever I am in the world. This is probably a pipe-dream. I’m never going to retire…

Field notes from Mexico 3 — Pulque Party

 

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Caution — drunkards. My favourite warning sign on the roads*. The source of their booze, the maguey plant, is on the left. Photo: Libertad Sanchez-Presa.

Once you leave the main roads and cities, a large amount of Mexican culture revolves around the Agave. Its most internationally renowned member is the blue agave, Agave tequilana, whose sugary heart is used to make tequila. A less well-known drink is mezcal, which can be made from a range of Agave species, and by small producers. This allows for a wide variety of styles and flavours, making it a more diverse and interesting drink than mass-market tequila.

In the region where we’ve been working, however, the dominant species is Agave americana, known as maguey. The plants are everywhere, either as dedicated plantations, scattered among crops, or surrounding houses and smallholdings. They’re not just a weed though; they are carefully tended and visited regularly to harvest the sugary sap from their core, known as aguamiel (honey water).

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The heart of the maguey plant contains a pool of sugary sap (aguamiel). In this case it is protected from evaporation and contamination by a plug of igneous rock.

During our hunt for the lost firs, which was a great adventure, we ended up walking through a number of farms in the foothills. In one we met a local woman collecting her aguamiel, who showed us how it was done. The process is pretty simple: a coke bottle with a hole in the bottom and a tube attached is used to suck the liquid straight out of the core, then drained into a bucket. She then scrapes out any scum or accretions on the bottom of the core, which ensures that the plant continues to secrete more sap through what is effectively an open wound. Most of her teeth were missing, which can probably be attributed to a lifetime of doing this.

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A local farmer near Metapec sucks the sap from the heart of a maguey plant using an improvised bottle with a tube attached.

She offered me some and, being generally willing to try everything, I naturally obliged. It’s sweet with a distinctive flavour, in this case enhanced by a number of dead flies which added an interesting mouth feel.

In some places you can buy the aguamiel pure, though one imagines they filter it first. Its most important value, however, is to be fermented into the mildly alcoholic** beverage pulque. As you drive through rural areas there are occasional improvised signs next to shacks declaring its availability. Pulque is sold by the litre***, dispensed into whatever container you have to hand. We’ve been using old plastic water bottles, though this makes them impossible to ever use for water again because the pulque leaves a lasting unpleasant odour in the bottle.

It’s best drunk fresh because it continues to ferment in the bottle, which shouldn’t be closed too tightly as the build-up of gas can cause it to explode, especially if you’re bumping along dirt roads as we tend to be. Left for too long it becomes viscous and unpleasant.

The drink is the favoured end-of-day beverage for labourers, serving the role that beer plays elsewhere in the world. It’s slightly sweet, frothy and refreshing. We’ve tried a number of pulque shacks and experienced the full range of quality. Some was delicious and moreish, another so bad that one sip had us spitting it out and feeling queasy for the rest of the day. We’ve been going for pulque natural, the pure version, although in many places you can buy it flavoured with fruit juices.

Pulque is also used to make the dish barbacoa, a speciality of the State of Higalgo, which is meat (usually pork) soaked in pulque, wrapped in maguey leaves and baked. The result is something like pulled pork; tender and juicy with a characteristic flavour. It can then be wrapped in a taco with the usual accompanying relishes.

Is there a potential mass market for pulque? Personally I doubt it. Achieving greater quality control and consistency would not be impossible, but the difficulties of transporting it and keeping it fresh mean it’s unlikely to supplant beer. In the villages and rural parts of the country, however, it remains an important part of daily life. It’s also a great way to finish a long, tiring day of fieldwork in the forest.


* Not, I should add, an official Mexican highways sign. Someone had stuck their own sign on top of the existing one. Drunkards of Mexico, we salute you.

** I sank a litre of it by myself a few nights ago. It didn’t get me anywhere even close to drunk but it did give me a vicious hangover. I won’t be trying that again.

*** We’ve paid 10–12 pesos per litre, which is around 50 pence.

Field notes from Mexico 2 — Lost Valley of the Firs


UPDATE: this post is followed by an embarrassing correction. I’m leaving the original in place, unchanged, because I don’t want to hide the fact that scientists sometimes (often) make mistakes, and are as prone to over-enthusiasm and optimism as anyone else. So please read on, and don’t judge us too harshly for admitting our errors. 


We have rediscovered Abies hidalgensis! This is an amazing find, and a real boost to the PinaceaeGo project. It took two solid days of hunting on inaccessible mountain slopes. To understand why this species is so important, we need to start at the beginning, with some fine detective work in the herbarium by awesome PhD student Libertad Sanchez-Presa.

Abies hidalgensis was first described in 1995 by a Hungarian botanist following a collecting expedition the previous year*. Unlike all the other ‘new’ species described in that paper, it survived subsequent critical review by Aljos Farjon, the world expert on conifers and a notorious lumper**. Libertad uncovered the type specimen in the National Herbarium of Mexico at UNAM in Mexico City. Everything about this species sounded dubious. The description of the collection locality didn’t match the co-ordinates, which were 30 km away. It was supposedly found at 2300 m altitude, whereas we haven’t seen Abies below 3000 m anywhere else in the country. Most of all, this is an arid area, and firs are usually found in dense, damp, dark forests. Nothing we saw on Google Earth suggested that such a location existed. She decided that this mysterious species was worth tracking down.

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This is the duplicate specimen of Abies hidalgensis held in the Kew herbarium (obtained via HerbWeb). That label is all the information we had to go on.

Our journey began with a drive up from Puebla to Tulancingo in the state of Hidalgo, where we spent the night. An early start took us to the vicinity of Metapec, a small village to the south of the mountain range where the species was described. From there we took dirt roads as far as we could towards the location described on the sheet, though the details couldn’t be matched to the actual landscape.

For one day we hacked up and down gulleys and over ridges, sweating in the heat. We saw some amazing stuff: a huge tarantula hawk wasp killing a large spider then dragging it away; a wild Mammillaria cactus with edible fruits, which we ate; some oak ‘apples’ (really galls formed by insects) large enough to deserve the name; and an array of spectacular mushrooms. Some of our findings will be the subject of a future post.

What we didn’t see were any fir trees. More concerning was that we didn’t even see any habitat where Abies was likely to be found. There was plenty of dry pine forest and scrubland, but even scanning the slopes and plunging into the valleys revealed no firs or even evidence that they might once have been there. By late afternoon we were tired and disheartened. Had the species disappeared? Did the collector get their field notes mixed up?  Was it an elaborate hoax? All sorts of explanations ran through our minds.

Typing the co-ordinates into my GPS gave a location 30 km away in the state of Veracruz. This was a long way from the site description, but it was at least up in higher mountains where Abies might more plausibly be found. There was nothing for it; we had to look. The actual driving distance was more like 50 km, ending up on dirt tracks in remote villages. All we found were large plantations of exotic trees that the locals referred to as ‘Chinese pine’ (perhaps Pinus koraiensis?). If the Abies had been there once then there was no sign of it now, nor of any native vegetation. We drove back, 100 km of wasted effort.

All the way back to Metapec we were haunted by visions of Abies in the forests around us. More than once we screeched to a halt, convinced that one or other of us had spotted something, only to discover it was just another Cupressus lusitanica. 

As we drove past the ridges we had been exploring earlier in the day, it was late evening, and the setting sun was illuminating the slopes. Sarah spotted some conical trees unlike anything we had seen that day. We pulled out the telescope and peered through the dusty haze. There was definitely something up there, tucked away in an inaccessible valley… but we had become rather jaded by our earlier experiences and were no longer willing to trust our eyes. Besides, it was 10 km away, and there was no hope of making it up that evening.

The next day we had plans to inspect another site, but made the difficult decision to try again, one last time. If it was there then it would be remarkable; if not then we were all ready to remove it from our biogeographical analyses as an aberration. We started out from a different point, navigating through the slopes towards the valley Sarah had identified from the road.

Emerging onto a ridge crest, it was Sarah who again noticed something unusual. On the next ridge north of us, atop an escarpment a few hundred metres away, a small tree was poking up with a distinctive conical form. It was only around two metres tall and, squinting through the telescope, it looked like it just might be an Abies. Reaching it would be extremely dangerous though. We pressed on.

We climbed further up until we reached a high ridge at 2600 m close to our target location. It was lunchtime and we were tired and hungry. We dropped bags and looked around the typical oak-alder forest. Libertad pointed towards something growing in the understorey. Could it be?

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Sarah celebrates finding the first Abies seedling. It’s just to the right of her.

She ran over and confirmed — we had an Abies! In fact, they were all around us. But at this altitude, in this vegetation, was extremely peculiar. It wasn’t anything like the normal conditions for Abies, nor in fact much like the site description from the herbarium records. None of this made much sense. As we descended down the opposite, north-facing side of the ridge, they were everywhere. The tallest individuals exceeded 20 m in height and 50 cm in diameter, with a range of sizes and plentiful seedlings. But they were growing in dry, open conditions, on a ridge with cacti nearby; how was this possible?

We only had a few hours before we needed to return home. In that time we managed to collect herbarium specimens, tissue samples in alcohol for genetic analyses, trait data for our own work and core two large stems***.  The steepness of the slopes, peppered with escarpments, made it impossible to descend far into the valley below, but we could see more Abies down there and on the opposite slope. Talking to a local farmer later that evening it sounds as though another route into the valley exists, which we may explore next time. We left as late as was safe, exhilarated and exhausted, and also a little frustrated at not being able to stay longer and collect more data.

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Two large, healthy specimens of Abies hidalgensis, right on an exposed ridge top. This is not where we would have expected to find them.

What now? We have the trait data we were looking for, and can confirm not only the presence of this species but also its exact location. Our samples will be sent to local herbariums and experts; hopefully the tissue samples will allow a systematist to determine the true place of this species on a phylogeny and identify its nearest relatives. We are also a little puzzled by the cones, which don’t look much like those on the existing herbarium specimens.

That’s not where this story should end though. The species is listed as vulnerable on the IUCN Red List, which is reasonable given that the range of this population can be no more than two square kilometres. One hot summer and a severe forest fire could severely deplete its numbers, a disaster which becomes increasingly likely in a warming climate. Having found the species again, we now bear some responsibility to do something about it.

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So far as we know, these two valleys encompass the global range of Abies hidalgensis. Rumour has it that there are some more close to the village of Agua Blanca to the north, but we were unable to confirm this.

What this action should be is something we will need to discuss. Perhaps we could undertake a comprehensive mapping exercise and population estimate; press for the designation of a protected area; collect seeds or propagate live material for ex situ conservation; set up a mapped forest dynamics plot… all could be the subject of future work.

Personally, I think the most important outcome should be a local education campaign. We spoke to many locals and farmers over the course of the two days, yet only one knew about the species. These are people for whom this forest is on their doorstep, who use it to hunt or collect firewood and mushrooms. Realising that their forest contains a tree of global importance and interest should be a matter of great pride, and will be the key to ensuring that it remains well protected.

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Libertad’s plant press contains that most precious of cargoes: herbarium specimens of Abies hidalgensis, the first to be collected for over 20 years, linked to a much greater amount of contextual information and data on the individual trees.


* Their visit is described briefly in this paper. They didn’t manage to see a great deal on their two trips up the mountain.

** Taxonomists are often broadly stereotyped as ‘splitters’ or ‘lumpers’. Splitters have a propensity to declare new species on the basis of fine differences among populations, sometimes as much through wishful thinking as meaningful variation. Lumpers review these designations and collapse them into single species. Splitters don’t like lumpers because they take ‘their’ species away. This tension has been present throughout the history of taxonomy.

*** Coring carries a small risk to the tree, and therefore should only be performed with a good reason and where you can be confident that there are plenty of individuals. From these cores we can determine the growth rates of the trees and look for any indication of climate dependence or changes over time.


IMPORTANT UPDATE (18 August 2016)

Well, as the new header on this post might have given away, we didn’t actually find Abies hidalgensis. We had grown increasingly suspicious of our collection over the days that followed, and on depositing the specimens in the herbarium at Monterrey, our fears were confirmed. We had actually collected Pseudotsuga menziesii. 

How did three experienced plant ecologists come to make such a big mistake? There are a few mitigating factors. Psuedotsuga  wasn’t previously recorded in this area, so we weren’t expecting to see it. We were tired, clutching at straws, and perhaps too ready to leap at anything that looked like an Abies. Finally, they aren’t that easy to tell apart. I should be embarrassed because I know Pseudotsuga menziesii well from North America (its common name is Douglas fir), but the local Mexican type actually looks very different, and some botanists have tried to designate it as a different species. I won’t comment on this other than to say that the accepted approach is to consider it as a single species with sub-specific variants and a high degree of morphological variation.

Where does this leave Abies hidalgensis? We still don’t know. The original collection records for the type specimens are contradictory and bear little resemblance to the landscape of the area. We tried everywhere that sounded roughly right, or that looked like it might be Abies habitat, and a lot of places that weren’t, just in case. We did everything we could to find this species in the time available and failed. Is it actually there at all? Was it ever? We are back to having some serious doubts about the very existence of this species.

As for our error, it’s an excellent demonstration of why scientists publish in journals rather than online blogs. When we submit a paper, as we would eventually have done, our findings go through many layers of careful scrutiny. It takes a long time, and many ideas fall by the wayside in the process. It’s easy to dash off a small blog post in the evening with a beer and claim quick credit, but were these to be treated as findings equivalent to published articles, it would carry the risk of mistakes ending up in the body of scientific knowledge. So you should never automatically trust a blog post, press release or similar non-standard means of transmitting a scientific finding. It may get more attention than a paper published years later, but it carries a high risk of being wrong, as we were.

Still, we had fun :o)

Field notes from Mexico 1 — Pinaceae Go!

For the next five weeks I’m based in Puebla, Mexico. It’s a beautiful location: an historic city (the centre is a World Heritage Site) surrounded by spectacular archaeological sites and with a horizon dominated by snow-capped volcanoes*. There’s not much time for tourism though; we have a packed itinerary.

The first three weeks will be taken up with a single mission: collecting trait data from as many Mexican coniferous species as we can find. Hence the nickname of the trip, Pinaceae Go!** Because finding real trees is way more fun than hunting virtual creatures on your mobile phone. We also stand a chance of spotting the legendary volcano rabbit, which sounds as though it should be a Pokémon.

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The Pinaceae Go team — myself, ecologist Dr Sarah Pierce and PhD student Libertad Sanchez-Presa. And, in the background, the real object of interest: Abies religiosa on La Malinche volcano.

Why Mexico? The reason is that the country is the centre of global diversity of conifers. Of the 120 recognised species of Pinus worldwide,  49 occur in Mexico***. The country also holds 7 of the 18 species of Cupressus, 8 of 48 species of Abies, one each of the four species of Pseudotsuga and Calocedrus, 3 of the 38 species of Picea and 20 of the 68 species of Juniperus. That’s quite a haul. Of those seven important genera, Mexico alone contains 30% of  global species richness.

So what? There are other centres of tree diversity all around the world. Why is this one in Mexico special?

The reason this particular hotspot baffles me is that current opinion in forest ecology suggests that conifers can’t reach high levels of species richness. This is because classical theory argues that conifers don’t have the flexibility of traits and growth forms available to broad-leaved trees. Conifers all have roughly similar branching patterns, leaves**** and wood. It’s relatively easy to understand how multiple broad-leaved tree species can coexist by having distinctive traits to reduce the degree of competition among them. Such a wide range of variation simply doesn’t exist in conifers.

This account may appear compelling to a temperate ecologist, who will know of the vast boreal forests containing only a couple of coniferous tree species. It falls apart when faced with the montane forests of Mexico.

To illustrate the scale of the problem, our very first sampling location provided a perfect example. We drove along a dirt track up the side of the famous active volcano Popocatépetl, stopping at around 3000 m altitude to have a look around the forests. It didn’t take long to start building our database. Within 100 m of the road we were able to sample five species of Pinus, one Abies and a Cupressus. We weren’t even trying very hard; this was an introductory walk to test our methods rather than a systematic sample.

Ultimately the questions Libertad would like to answer include:

  • At what spatial scales does the coexistence of so many species of conifer occur? Are they growing side-by-side, or specialising on distinct types of habitat?
  • Do the traits of conifers determine which species are found in coexistence? Do these traits change among locations or depending on the presence of other competing species?
  •  What drives patterns of species and trait diversity in conifers on biogeographical scales?

We’re only at the beginning of this project; Libertad is still in the first year of her PhD and this is the first fieldwork we’ve done. A large amount of trait data is in the literature already, along with the Mexican national forest survey. We’ve been processing all this information over the last few months. Our aim for this trip is to supplement this with missing species and new locations. Gotta catch them all…


* Your view of snow-capped volcanoes may depend upon air quality.

** Conifers include the pines (Pinaceae), hence the trip nickname. Conifer Go would have been more accurate, but wouldn’t have sounded as good.

*** Let’s not get into arguments over taxonomy. We’re following the opinion of Aljos Farjon, generally acknowledged as the world expert on conifer systematics, and bane of splitters.

*** Yes, they are still leaves, even if they are colloquially referred to as needles.

The four types of plants

Botany has an image problem. Part of the issue is that it’s perceived as possessing arcane and esoteric language, making it impenetrable to outsiders. There is some justification in this; an average reader would need a large glossary to hand in order to tackle the more recondite specialist floras. That said, for readers in the UK, there are excellent and accessible floras that anyone can use, which, combined with a guide to plant families should be enough to set anyone on the right path.

As Kew Gardens’ recent State of the World’s Plants report attests, there are almost 400,000 known plant species, a number which is only set to increase. This is daunting complexity. There have therefore been multiple attempts to simplify the diversity of plants into a set of categories, based on their taxonomy, appearance or function, to help break down the problem into manageable chunks.

One of the most influential attempts to do this was by the great Danish botanist Christen Raunkiær, a founding figure in plant ecology, who recognised a series of plant life forms:

 

Raunkiaer1907-life_forms-small

Plant life forms as determined by Raunkiaer (1907). Plant parts are distinguished between those which are ephemeral or temporary (thin lines) and those which persist through unfavourable seasons such as cold winters (dark lines). Names are given in the text.

These sketches appear to be straightforward divisions. One could easily map them onto common vernacular terms: tree, shrub, vine and so forth. Alas, would that it were so easy. The numbers on the above figure actually correspond to another set of impenetrable terms: (1) phanerophyte; (2–3) chamaephytes; (4) hemicryptophyte; (5–9) cryptophytes which include (5–6) geophytes, (7) helophytes and (8–9) hydrophytes. Many of these are subdivided further, and some others are not even shown in this figure  (therophytes, aerophytes and epiphytes).

If you know a little Greek then all these names have sensible, intuitive meanings. If you don’t know any Greek — and let’s be honest, most people don’t — then this is a barrier.

That’s why, when I start my undergraduate botany classes, I make it much, much simpler. To begin with, there are only four types of plants, defined by function. These are:

  1. Plants you can eat
  2. Plants you can kill people with
  3. Plants you can use to get high
  4. The rest

Learn the first three, and the rest will come naturally. Below are some examples. One species you can eat (Eruca sativa, otherwise known as wild rocket or arugula), one you can kill people with (Aconitum napellus, perhaps the most poisonous plant in the northern hemisphere), and one you can smoke (Leonitis leonurus, a South African plant known as wild dagga).

I can spin a yarn around each of these species that leads on to important botanical understanding. The first time I pick up a clump of Eruca sativa and pass it round for students to taste, many are reluctant. A few will take a cautious bite then spit it out and declare it to be inedible. Only when you tell them that it’s rocket and a constituent of most salads do they give it a fair try. Within Europe, anything with that type of flower — four petals in the shape of a cross, white or yellow — is edible.* They are the characters identifying the Brassicaceae, an important plant family. One down already!

Poisons tick off a wide range of families, and are associated with great stories. Monkshood, Aconitum napellus, is seldom found growing wild in the UK. Most of its known sites are on the grounds of former nunneries. Why would nuns need poison? The answer is that is had another unpleasant traditional role: as an abortificant. In carefully-controlled low doses it was enough to provoke abortions, though the experience must have been horrendous, not to mention dangerous. Still, for the nuns, it was better to cover up indiscretions than risk scandal.

Psychoactive plants are harder to come by in Europe, but when you find one they generate disproportionate interest among students. Leonitis leonurus is an innocuous-looking garden shrub. If you want something to smoke, select the developing flower buds or, if none are available, the youngest leaves, because this is where the interesting chemicals are concentrated (which might remind you of another useful plant). It has this in common with many other plants, such as the tannins in tea leaves, because those chemicals we enjoy for their neurological effects are actually deterrent toxins aimed at browsing insects. They concentrate in the tissues that are most valuable to the plants. Come for the drugs, stay for the important lesson on plant defensive investment strategies.

Once you make the stories of plants personal, botany becomes more accessible, and more interesting. All it takes to engage a group of sceptical zoology undergraduates is to show them that first step. The rest can take a lifetime.


*  There are a few exceptions, like Potentilla erecta (tomentil; actually Rosaceae), or cases where coloured sepals can confuse the unwary botanist (e.g. the golden saxifrages, Chrysosplenium spp.). These aren’t toxic but do taste terrible, so you’d soon spit them out, thereby learning another botanical lesson.

All images taken from Wikimedia Commons