Tuesday, August 28, 2012

What's the name of this plant again?





Species name: Ginkgo biloba

Common name: ginkgo, maidenhair tree

Location: Ontario

Up until relatively recently (late 1700s to early 1800s), this species of tree was well known from the fossil record (along with the approximately 8 other species in the genus) but believed to be extinct in the wild. There were a few living specimens known at the time in China, Korea and Japan that had been cultivated and tended by monks for thousands of years, and so they were considered to be, quite literally, living fossils. Two stands of trees were discovered in China and from those two remaining small populations, all of the rest of the trees in cultivation around the world were derived. Unfortunately, it was discovered recently that the two remaining natural populations show an incredibly high level of genetic uniformity (suggesting they might, in fact, be two "families" of trees and therefore very closely related to each other) which puts them at great risk should a pathogen develop that targets ginkgo trees. This probably isn't an "if" and more a "when"! Like bananas, all of the ginkgo trees would be wiped out if we couldn't come up with a solution in time. Similarly to the Dawn redwood, the ginkgo tree is monotypic, meaning that it is the only remaining species in the genus, and all of the rest of the close relatives to this species are known only from fossils. You can read all about the Dawn redwood HERE. Interestingly enough, the Dawn redwood, like the ginkgo, is also critically endangered in the wild.

There are two characteristics about the ginkgo that are worth noting. The first is that these trees are dioecious, meaning that there are separate male and female trees. If you're planting a ginkgo tree on your property for purely ornamental purposes, make sure you choose a male tree! The female trees are the ones that bear the fruits, and the fruits have a hideous smell (think of the smell of rotting, rancid butter and that will begin to describe it...) that lingers throughout the winter with every temporary melt of snow. If you would like to plant the tree to consume the seeds for their reported medicinal values, make sure you plant both a male and a female tree to ensure large amounts of seed production. The second interesting characteristic about this tree is that they don't actually produce fruit, because fruit can only be produced by Angiosperm trees and this is a Gymnosperm. This means that the ginkgo, despite looking like it has broad leaves (similar to something like a maple or aspen or oak) it actually has modified needles (like pine or spruce or a cycad)! The "fruits" are actually just seeds with a swollen outer surface called a sarcotesta, and is developmentally very different than the fleshy part of a fruit. Once that layer is removed (should you attempt this insane, smelly feat, WEAR GLOVES! The smell, once on your skin, has to be leeched out, not washed out!), the remaining seed "shell", the sclerotesta is revealed and it looks a whole lot like an unopened pistachio (but a lot bigger).

The ginkgo seeds are culinary delicacies in many locations around the world, not the least of which being in China where it is used in large amounts around Chinese New Year in a dish called Buddha's Delight (if you've never tried it, you must! It's delicious). The Japanese and Koreans also make dishes that feature the ginkgo seed, and they are served year-round (but more so on special occasions since they are expensive). The other main use of this plant aside from its culinary and ornamental uses is the medicinal use. This is actually one of the suggested reasons for the decline of the population of ginkgo trees throughout its native range. Other theories state that massive ecological changes caused drastic declines in population and the ongoing medicinal value of the plant was the straw that broke the camel's back, so to speak. Regardless, there are now plantations in China for the dedicated medicinal use of this plant.

Medicinally, the main claims to fame with ginkgo and human health revolve around memory and dementia. First, it is claimed that ginkgo supplements help with memory retention in the aging process. It is suggested that if you consume 240 mg of ginkgo extract per day it will improve your long-term memory and help prevent the onset of Alzheimer's disease. In a very large study in 2008 done by the Journal of the American Medical Association, there was no effect of ginkgo extract consumption and memory, or a correlation between ginkgo consumption in any form and the onset of Alzheimer's. People who consumed ginkgo were just as likely to get it as those that didn't. A much smaller study in 2010 by the American Geriatric Society published in the Journal of Geriatric Psychiatry showed that it had a significant effect over a placebo in people already suffering from Alzheimer's (or other diseases that are Alzheimer's-like) on memory retention. A third study showed that for up to 2.5 hours after consumption, ginkgo extract and ginkgo seeds had a significant effect on memory retention in memory-recall experiments in healthy people. So far there are no studies that show that ginkgo is harmful to your health, so if you choose to take it to improve your memory at the very least it will do nothing. But until more large-scale scientific studies start agreeing with each other, take all reported effects with a grain of salt.

Ginkgo extract does act as an anti-coagulant, so as with all medications (herbal or not), make sure you consult a doctor before taking them to make sure it won't interfere with anything you're already taking. This especially applies to those at high-risk of stroke who are already on blood-thinners like warfarin (yes, the rat poison warfarin is now a medication for humans!) or coumadin, since even a minor injury could lead to massive blood loss.