In Museo del Palazzo Massimo in Rome there's a mosaic showing a plate holding a few fruits. Among these there's one that really looks like a pineapple. Apparently, though, pineapples were imported to Europe by Columbus from the Americas.
So what is the fruit portrayed?
Is it really possible that Romans crossed the Ocean, somehow?
Or maybe there were, say, variations of pineapples that grew in Africa or Middle East or Asia that reached Rome via trade?
My main question is: what's the most likely hypothesis?
Here's a picture: https://staticfanpage.akamaized.net/wp-content/uploads/sites/12/2015/04/ananas-roma-02.jpg
Given the choices,
There's no doubt the second is more economical.
One agriculturalist in the 1950s, Domenico Casella, is the origin of the idea that it must be a pineapple, even though it's not much bigger than the pomegranates next to it. The people who take up this theory tend to be not in the fields of archaeobotany or Roman archaeology: people like the anthropologist George Carter, the botanist E. D. Merrill, the Africanist Ivan van Sertima, the conspiracy theorist Gunnar Thompson (who made up a fiction that there are loads of pineapples in Roman art).
Some archaeobotanists like Wilhelmina Jashemski identify it as an umbrella pine cone, which is a common motif in Pompeian art and regularly appears in food dishes, especially on altars. The Romans did eat umbrella pine nuts. Jashemski cites as examples a fresco at the Casa dell' ara massima, with a pinecone placed among eggs and dates; other frescoes at the Casa del Cenacolo, and at the bakery on the Via dell' Abbondanza; and a marble tablet in the House of the Golden Cupids "showing an altar with a plate piled high with fruit and a large pinecone."
She notes that the pinecones are typically depicted with the scales tightly closed, as in this mosaic. She suggests that the purpose of the pinecone could be tied to its resonances in Dionysiac cult. I'd suggest something simpler: you can eat umbrella pine nuts, and the cone happens to be a cool decoration.
Edit: apparently the umbrella pine is more often called the stone pine. Here's a sample of how the cone looks with the scales closed and still green.