Marmelades can't be made from carrots in the EU, we have the Brits to thank for that who insisted that the term is restricted to citrus fruit, the rest is jam. Especially nuts because the term derives from Portuguese "marmelada", quince mush, and quinces are definitely not citrus fruit.
Speaking of the Portuguese yes they gave us that classification of carrots as fruits so they didn't have to call their stuff "carrot spread" or something. Noone else on the continent cares, it doesn't have any impact on anything else, and next time definitions are re-done they might just leave out the "has to be fruit" part in the definition of jam, or "fruits, or vegetables traditionally used for jam, or with sufficient fruit-like character".
I guess some lines have to be drawn though otherwise Nutella is going to start calling itself hazelnut jam.
In reality it really does not matter and the classification is somewhat arbitrary. Just think about adding it to a fruit salad. Would you do it? Then it's a fruit.
I once saw a little blurb at a sandwich shop stating that tomatoes are fruit, but if you pair them on a sandwich with jalapenos, you're getting both fruits and vegetables. I demand better scientific accuracy in restaurant marketing signs.
Very much so. Bell peppers and jalapenos are fruits from different strains of capsicum annuum. Biologists apparently don't agree on whether all chilli/paprika stuff is capsicum annuum, what's for sure is that they're all very closely related.
To add to this, vegetable is a culinary term and not a scientific term. Whereas, fruit can be both. Tomatoes are scientifically a fruit, but generally not from a culinary perspective.
This is precisely it: Tomatoes can be sweet enough to be a fruit, they can be acidic enough to be a fruit, but they're definitely too umami to be fruit.
Next thing people are going to insist on, wilfully ignoring the differences in taxonomy, is that peppercorns are fruit. A stone fruit, just like cherries or peaches.