Category Archives: Gardening

Sweet Potato Awareness Month

November is Sweet Potato Awareness Month (SPAM), and I do my part by reminding people that yams are something else entirely. As a foodie and an evolutionary biologist, I feel obliged to be a nudge about this. So here are three images to help.

First, a photograph of a white yam (Ipomoea rotunda) in a bin of sweet potatoes.

Colin Purrington Photography: Blog photos &emdash; A white yam (Dioscorea rotundata) in a bin of sweet potatoes (Ipomoea batatas)

Second, a photograph of three cultivars of sweet potato (all Ipomoea batatas) next to a yellow yam (Dioscorea cayennensis).

Photograph of sweet potatoes and yam

Third, an illustration of how yams and sweet potato are related (they aren’t). As a bonus, I’ve also indicated the position of potato.


Please share this page with your family prior to Thanksgiving dinner. It will be one less thing to bicker about. If you need more details, here’s my “Yams versus sweet potatoes” page. Read it if you want to know why the slave trade caused the whole “yam” confusion problem.

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Distinguishing tobacco and tomato hornworm caterpillars

After agonizing over the identification of hornworm larvae for years, I’ve developed two tricks that I’d like to share. Tobacco hornworm (Manduca sexta) caterpillars have stripes (seven of them), so remember that by thinking of Lucky Strikes cigarettes. Horn is usually red or red-tipped, like a cigarette. Also, tobacco gives you dark teeth and lungs … and tobacco hornworms have black shadows on their stripes. Tomato hornworms (Manduca quinquemaculata) have eight chevrons (Vs), which you can remember by thinking of V8 juice, which is primarily tomato juice. Here’s the graphic you can share with friends who might have it wrong:

Photographs of tobacco and tomato hornworm caterpillars

If you can, please spread the word … most of the tens of thousands of tobacco hornworm photographs on the internet are misidentified as tomato hornworms. Even Wikipedia page for tomato hornworm shows tobacco hornworm larvae (I’m working on it …). The problem is that tobacco hornworm eats tomatoes, and people with fancy cameras grow a lot of tomatoes.

For people living in Hawaii, please note that the above doesn’t include Manduca blackburni, which is closely related to tomato hornworm.

Photograph of tomato hornworm from Amanda Hill.

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Minor victory in my war against yam labeling fraud

In my futile quest to convince people that sweet potatoes shouldn’t be called yams (which are unrelated plants), I discovered that one can actually report vendors who label sweet potatoes as yams. So, for giggles, I reported Giant Foods to the USDA’s Misbranding and Misrepresentation Office. Below is a photograph I took in November of their organic sweet potatoes:

giant-sweet-potato-05 (1)

And now in all of their stores (that I’ve checked), they sell sweet potatoes labeled as sweet potatoes:

Nature's Promise sweet potato at Giant

It might be a small victory, but Giant Foods is giant, so I’m pleased. If you want to know more about my futile war, please see my page on Yams versus Sweet Potatoes. If you want to make your own report, just visit the above USDA site and send the contact person a photograph of the label along with store contact information. They’ll do the rest, and apparently in a persuasive way.

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