Mexican White Pines are better than our own White Pines in our own climate?!

Species name: Pinus ayacahuite

Common name: Mexican white pine, ayacahuite

Location: Western University campus

I have my suspicions about this tree, and it has nothing to do with the identification. There are three Mexican white pines all planted in a pretty clump; they are definitely ornamental trees and were planted after the arboretum was established on campus (so, believe it or not, these trees are younger than I am. Boy do they grow fast! Because...I'm not that old, no matter what my students would lead you to believe). They are most definitely Mexican white pines. What I have my suspicions about is their distribution and abundance. They are native to three very, very small pockets in Mexico along parts of the mountain range that runs straight through the middle of Mexico. These three pockets are now independent populations, and at the time of their assessment under the IUCN (the International Union on the Conservation of Nature) the three populations were non-interbreeding. This in itself isn't necessarily a big deal, but it's the rest of it that matters. Mexico is undergoing, like many countries in Latin America, a huge shift from rural rolling landscapes where you won't see a person for miles into a highly urbanized country with extensive urban sprawl. On top of that, all of these "Eco Resorts" are popping up all over the country. And then there's the drug running (there's no point in denying that it exists!). Oh, and on top of all of that the conversion from traditional vegeculture multi-crop agriculture to a more "North American" (I hate that description for it, since Mexico is part of North America) method of monoculture agriculture. These four things in combination amount to a lot of deforestation; doing this in an area that already contains three highly fragmented populations of a species, populations that exist nowhere else, probably means that the "Least Concern" status that this species has according to the IUCN is now incorrect. I would bet that at least one of those three populations no longer exists, and that the status of the species should, at minimum, be category NT or "Near Threatened", if not VU or "Vulnerable." But, as with all biodiversity research, you first need to find an organization that will fund the research to go out and study these populations (which hasn't been done since 1994!). To say this is a "Mexican problem," or even a "Third World problem," would be completely incorrect. Under the current economic climate in Canada, the only species reassessments done for species at risk are for species that grow in economically significant areas (like the Tar Sands in Alberta), or in areas where urbanization is slated to occur (in the case of Environmental Assessments). I like to think that Canada is a pretty "developed" country...!

Not having the funding to do diversity studies and study species distributions isn't something that can be restricted to a specific geographic region. It's something we, as human beings inhabiting the world, need to think about. Where are our future medicines going to come from? Nearly 95% of medicines around the world are plant-based or plant-derived (or once plant-derived but now synthesized in the lab). Many of our most successful early cancer treatments originate from plants (taxol is the first one that jumps to mind, and you can read all about the plant that taxol comes from HERE). Our most widely prescribed (and most would argue, for good reason, over-prescribed) antibiotic comes from a fungus (penicillin from the Penicillium fungus). And where would we be without wine (grapes and an alcohol-fermenting fungus) or tequilla (agave and an alcohol-fermenting fungus)?! It would be a sad case indeed. Anyway, onto happier things, like talking about Mexican white pines... :)

The Mexican white pine is one of the most widely planted pulp trees, from which we derive paper. Nearly every large paper-producing country in the world (except Canada) plants the Mexican white pine as opposed to any other white pine species. This is because it is highly disease-resistant (especially to white pine blister rust, which is an ever-increasing problem in Canada and the United States, attacking all of our native white pine species), highly cold-tolerant (despite being from tropical Mexico, it can withstand temperatures of -30 degrees Celsius!), and highly drought-tolerant. This makes it ideal for planting in hot, dry countries, hot, wet countries, cold, dry countries, and cold, wet countries. Name a country that doesn't fall into one of those categories! I dare you :) Because of their large cones, and soft, feathery needles they are also a highly prized ornamental species. One great thing about this tree that makes it ideal to plant as an ornamental is that it doesn't actually get to be that large. The tallest Mexican white pine on record lives in Germany and is only 20 meters tall. That's not a very big tree for being the biggest ever recorded!

The Japanese can't make their own taxol from their yew

Species name: Taxus cuspidata

Common name: Japanese yew

Location: Ontario

You might be wondering why I'm featuring the same plant twice in the same week, but you would have made one vital assumption that is incorrect: just because two species look the same doesn't mean they are the same. The Japanese yew, featured here (native to Japan, as you might have guessed), is a very close relative to the Canada yew, featured in my blog post on Monday (read all about it HERE). In fact, by assuming that the photos above represented the same species as that of the Canada yew, you would be making the same error that many botanists have made in the past; it was only recently demonstrated that there are distinct species within the genus Taxus. The genus was originally thought to be monotypic, and instead having distinct geographic races or subspecies that are on their way to becoming their own species, but have not yet become distinct enough to warrant the title. The Sumatran and the Mexican yews are the most different from the type species, the European yew. These were the first to obtain their own species designation, with every other species following suit and being confirmed through DNA sequencing.

So if these species are so morphologically similar, how do you tell them apart? Well, the needles and their arrangement on the branches is the first clue. The needles of the Canada yew are arranged around the branches when young, but the development of the bark on the branches almost flattens out the arrangement of the needles as it matures. If you look at the branches that are brown in colour instead of green (showing that bark has been formed), the needles are in two rows on each side, but are flattened on the branch. It has almost become two-dimensional. The difference in the maturation of the Japanese yew branches is that the needles remain spirally-arranged on the branch; they never flatten out unless something has been grazing the branches. With age, the needles also turn upwards, so all of the oldest needles on the inside of the shrub or small tree are pointing upwards, even though their point of attachment on the branch is all the way around it.

The second hint that these are different species is their sheer size difference. The Canada yew barely reaches a height of 2 meters off the ground and completely lacks a central stem. While the Japanese yew pictured above doesn't really look like it has a central stem, it is clearly more "tree-like", and the branches have the ability to support their own weight as opposed to drooping onto the ground like the Canada yew branches do. The Japanese yew can also grow to a maximum height of 18 meters.

The last major differences are not visible to the eye, but rather "visible" to a machine called a gas chromatography mass spectrophotometer, or GCMS. These machines are also sometimes called the "mass spec," and if you watch CSI at all you will have heard of them! They really do exist, and they are used in much the same way as suggested on TV (but not nearly as quickly, and the results are a bit harder to interpret than what the shows make them out to be!). You dissolve a bit of an unknown substance into a solvent (usually some sort of alcohol, although other organic solutions are sometimes used like chloroform), and inject a very small quantity into the machine. The machine separates the individual components of the liquid mixture by molecular size, and displays a graph of molecular weight versus abundance. The shape of the peak tells you what types of chemical bonds are present, and the location along the size axis tell you how big the molecules are. The height of the peaks tell you how much of any given substance are present. So what does this have to do with the Japanese yew? Well, it's a rather unfortunate tale for the Japanese; if they want to make their own paclitaxel, they're going to have to start planting Canada yew. The Japanese yew doesn't contain the right combination of taxanes to have the desired medical effects. In fact, the Japanese yew is exponentially more toxic than the Canada yew; it has the distinction of being the "Japanese horse killer." Just five needles are enough to kill a small dog. If you choose to plant this ornamental tree in your garden, please keep animals and small children away from it! And don't EVER use it as a Christmas tree!

Taxol in plant form

Species name: Taxus canadensis

Common name: Canada Yew

Location: Ontario

The Canada yew is an incredibly important shrub to people all over the world, and most don't even realize it. While technically not a tree, most of its closest relatives can be up to 25 meters high. The Canada yew has no main trunk, and so just kind of flops onto the ground. It was originally thought to be a subspecies of the English yew, Taxus baccata, but was shown to be a distinct species through DNA sequencing and actually more closely related to the Western yew than the English yew! Just goes to show that plants that appear to be closely related based on morphology alone might be misleading you when it comes to their genetic relatedness.

The Pacific or Western yew has just recently been downgraded from threatened to nearly threatened on the IUCN's Red List of endangered and threatened species worldwide. Its eastern relative, the Canada yew, has now replaced the Western yew as a commercial shrub. So why the need to produce it commercially? Well, it is an incredibly attractive plant with its red arils and soft green needles. The arils of these plants, contrary to what they look like, are not fruits! Yes, they're soft and fleshy and contain a seed. But because conifers cannot produce fruits because they do not have flowers, the red arils can't possibly be fruits. Instead they're just highly modified seed coats, which have been modified to store sugars and other tasty things that are attractive to birds and small mammals. Unfortunately, these red arils are also attractive to children and lead to quite a few deaths or hospitalizations every year since the seeds are incredibly toxic. The animals that consume the yew arils only eat the fleshy outsides, and either swallow the seeds whole and pass them right through their digestive tract, or leave the black seeds behind.

Sure, the ornamental use of this plant is quite important in Canadian industry. But that's certainly not the most important use of this plant worldwide. In the late 1980s and early 1990s, this plant was discovered to have a unique set of chemicals called taxanes with an incredibly important role in human health: they kill cancer cells. The chemicals were first isolated in 1992, and lead to the widespread population decline of the Pacific yew in western Canada. The Canada yew in the east was then discovered to have just as high a concentration of taxanes that were just as easily purified from the bark, and this species is much more abundant. It can also be sustainably harvested every 5 or so years, and so the purification of taxanes was switched to the bark of the Canada yew. Once the process was perfected and clinical trials were completed, drugs were officially put into production; worldwide they're called paclitaxel (the generic name) or taxol (the brand name). These two drugs are now the most widely prescribed anti-cancer drugs around the world. The other reason why this is so significant? The research was done at the university that I currently attend, The University of Western Ontario in London. Hometown pride! While there are still some stands of the Canada yew being used for taxane production, some of these chemicals have been successfully synthesized in the lab. It's only a matter of time before the entire spectrum of taxanes can be artificially lab-created and so wild populations of both species can be left to their own devices.

The medicinal use of the Canada yew doesn't stop there, but any medicinal use of this plant is incredibly dangerous because it is deadly toxic. Native North Americans used the young tips of this plant in very small amounts steeped in tea and consumed to alleviate rheumatism. There is some clinical evidence that consumption of this plant is effective in this way for rheumatism, but it is a very fine line between an appropriate medical dose and a lethal or very toxic one. For this reason, most doctors (and even herbalists) prefer other routes of relief.