On Tuesday, the BBC decried the end of the 10-year reign of  the eight-pound Manx Potato as the world's heaviest. Its record had apparently been uprooted by a 25-pound spud from Lebanon.  In photos, circulated across the Internet, farmer Khalil Semhat hoists his misshapen tuber up like a proud father.

"I didn't use any chemicals at all," Semhat proclaimed to Agence France-Presse. "I've been working the land since I was a boy, and it's the first time I've seen anything like it."

The Manx's owner, Nigel Kermode of the Isle of Man, reluctantly conceded the crown: "We're still a world champion – we'll call it the second biggest potato in the world."  His decade-old  tater was reportedly "grey and brown" and hadn't been on display for quite a while.

But experts contacted by Scientific American say that Kermode has nothing to concede.  This is all a case of mistaken identity. Michigan State University potato expert David Douches says the vegetable in Semhat's hands looks an awful lot like a sweet potato – a crop more closely related to morning glory flowers than to hash browns. 

To settle the matter, we decided to talk to Kenneth Pecota, a plant breeder who has spent 15 years working on roots as part of North Carolina State University's (NCSU) Potato and Sweetpotato Breeding and Genetics Program.

[The following is an edited transcript]

What type of vegetable is Semhat holding in the photo?

It sure looks like a sweet potato to me.  Everything about it, the skin color, the skin peeling off with the white underneath -- that's very common in big, sweet potatoes.  When the sweet potatoes get big like that, that cracking is extremely common.  You also have the veins, which are little fibrous roots growing under the surface, that's very common with sweet potatoes as well.  We see stuff like that all the time at NCSU.

I don’t think he has a potato, I think he has a sweet potato.  I'm guessing that there was confusion somewhere in the translation. It's probably a language thing.

Well, perhaps it's a record-breaking sweet potato?

No, not even close.  We had one that size this year, and we're not even trying to grow them big.  Sweet potatoes are perennial and they'll just keep growing.  If he's got a long growing season in Lebanon, which I'm guessing he does, or if you space them out and give them optimal growing conditions -- 20, 30- plus pounds is not even uncommon.  It's big but it's not out of the realm.

I think there was a person that made the news, Janice Bohac, who used to be the sweet potato breeder at the USDA. She was toying around with a 41-pound sweet potato for ethanol production.

His is not even near the record.  [Though] it might be up for the ugliest one!

[According to the 2007 Guinness World Records, the world's largest sweet potato was 81 pounds.]

What's the difference between a potato and a sweet potato?

A sweet potato is a modified root and a potato is a modified stem and, therefore, a [true] tuber.  One of the big differences is that the sweet potato is a perennial and they continue to grow indefinitely while a potato has a predetermined length of season after which the plant will senesce and you're done, which is probably why your biggest potato is in the eight-pound range.

Both of their origins are in northern South America, Peru and up into Central America.  Probably the same people domesticated both the potato and the sweet potato. Sweet potatoes were more of a hot weather plant and potatoes were more of an up land, cooler crop.

What determines how big they can get?

A lot of it just has to do with how many roots you set. When you get these big ones, it's typically a plant that, for whatever reason, only has one sweet potato on it, and all the energy goes into that one.  It's the same way you get those giant pumpkins: you've got to pinch those other fruits off.  The second thing is it's probably a plant that had unlimited resources, like if the plant next to it has died. You have one big plant that has one root, and it pumps all the energy into that.

One problem with big sweet potatoes is the outer layer can't keep up the growth rate of the inner part, so it starts to crack.  Then, of course, you get disease organisms inside and they rot.  It's actually hard to get really huge ones because of that.

That Lebanese sweet potato was probably accidental.  But if you want to grow giant sweet potatoes, just spread them out.

So you wouldn't want to eat that giant, cracked sweet potato?

No, I'd peel that thing up, and it would be fine. I'd dice it up, steam it, or use it as a soup base.  A guy just gave me one at the farmer's market. He had a 5.5 pound sweet potato and said, "I don't know what to do with this, I can't sell it." I knew what to do with it.  I took it and made soup out of it, and it was great.