The Eden Project has rejected claims that it is anti-American, and not much of a garden.
Eden Project: "A farrago of false statistics and economic gibberish"
Tom Palmer of US think-tank the Cato Institute visited the futuristic domed greenhouses of the Cornwall conservation project last Christmas.
And writing in The Spectator magazine, he called Eden "A farrago of false statistics, economic gibberish and pseudo science, all neatly contained in a second-rate terrarium."
He told the BBC Today programme: "I was a little disappointed with the gardening, but I was shocked by the false information."
I put my hand up completely to the cock-up theory of life
He held up an erroneous sign in the visitor's hall as an example of several.
The sign said: If we could boil the world's population down to 100 and keep all the ratios the same, six people would possess the entire world's wealth, and they would be from the United States.
Mr Palmer said: "That's wrong for several reasons.
"The United States does not have 6% of the world's population, and does not control 59% of the world's wealth.
"There was a clear, hateful anti-Americanism in that, of the sort that you would only associate with anti-Semitism."
Tim Smit, chief executive and co-founder, said: "I am rather gob-smacked by this, because accusing me of being anti-American is the opposite of the case.
"I put my hand up completely to the cock-up theory of life.
"There was one sign in the ticket hall which does say that, he is right.
"But it has been taken down. It was taken down even before he wrote his article."
We have kept away from the, if you want, the open-toed sandal, nut-cutlet eating extremist environmental brigade
He explained: "I was sent a bit of internet spam by a friend of the project, and it purported to be from UN figures.
"In the ticket office we had a huge globe and I rather liked the idea of shrinking the world's population to 100 because there were some useful statistics there, as well as the ones that we were wrong, to which I own up.
"But to accuse us of anti-Americanism is ridiculous, and in this case anti-Semitism - is a little bit hysterical."
He said that Eden had worked with Coca-Cola, Boeing and had an American professor working at the site.
He added: "We are completely apolitical.
"We have kept away from the, if you want, the open-toed sandal, nut-cutlet eating extremist environmental brigade which he has such a horror of.
"So to be accused of it is a matter of great disappointment."
Mr Smit also responded to claims that Eden was a "second rate terrarium".
"If he was within a foot of me, I would bloody his nose," he said.
"It's the best garden in the world.
"There is no garden that has been created that has used a 34-acre tip with no life in it whatsoever and brought it to life.
"I read the article and wept."