Cashews

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I love cashews. I can't seem to get enough of them. Did you know that when you eat a cashew, you are only experiencing part of the fruit? Indeed, cashews are kind of weird and many of us in temperate climates never get a chance to fully appreciate what the cashew has to offer. You may also be surprised to learn that cashews and poison ivy are cousins.

Cashews or Anacardium occidentale as they are known scientifically are large trees belonging to the family Anacardiaceae. This makes them cousins of plants like poison ivy, sumac, pistachio, and mango (just to name a few). Like other members of this family, cashews produce chemicals that can cause severe skin allergies in humans. For cashews, this chemical is known as anacardic acid and is similar in its chemical makeup to urushiol. Because of this, cashews must be roasted before they can be sold. 

As I stated above, the cashew "nut" is only part of the reproductive effort of this species. They are not nuts in the true sense but rather a drupe similar to the pit of a cherry or peach. The drupes themselves hang from the bottom of a much larger accessory fruit called a cashew apple. This pear-shaped pseudocarp is quite juicy and does not ship well. Though it is a delicacy in tropical climates where these trees are cultivated, it rarely makes it to more temperate climates.

Cashews are currently native only to Brazil but fossils found in Eocene deposits from Germany hint at a much wider distribution. It is now believed that the group that gave rise to cashews originated in Africa and subsequently migrated outwards while South America was still attached. Today, the cashew is regaining some of its lost ground thanks to its agricultural importance. 

Speaking of agriculture, cashews are offering an interesting model for more sustainable farming practices. Cashews, like most other crops, are grown in large-scale monocultures. Thousands of gallons of pesticides are used on these crops to stave off pests. However, the pesticides kill more than just unwanted insects. What is interesting about cashews is that they naturally produce extrafloral nectaries (glands that secrete nectar) on their leaves. In the wild these glands attract ants looking for a high energy meal. The ants in turn guard these nectar sources from anything that may interfere with their feeding. As such, many potential pests are driven off by the ants. Research is being done to compare the rates of insect pests between cashew plantations that use pesticides and those that don't. It could be possible that by allowing ants to guard these nectar sources, farmers could avoid the use of pesticides to control insect damage. More work is needed but cashews are certainly a great model for developing such a system. 

www.indefenseofplants.com

Photo Credit: Peter Nijenhuis (http://bit.ly/1A0MmLI)

Further Reading:

http://www.jstor.org/stable/10.1086/520728

http://www.amjbot.org/content/85/6/835.full.pdf