Sounds like it might be a jerusalem artichoke (helianthus tuberosus), or a sunflower variety called helianthus salicifolius, which flowers late. Phil J

Funnily enough, I have just eaten some Jerusalem Artichokes tonight Phil...

Just waiting for the after effects... Lol.

Probably need a photo for confirmation guest.

We were recently, late September, in Austria and noticed that the sunflowers that they grow there could be described as a 'multi headed bush' rather than the single stem varieties that we grow in the UK. One of the gardeners had removed all the side shoots from his plants so that they grew as a single flower.

There are as you say multi-headed strains of Helianthus annuus so wondered if it could indeed be one of those.

There are a number of multi-headed sunflowers sold in the U.S.A. for ornamental purposes. Their seeds are also edible, but hard to handle and shell, due to the smaller size--still excellent bird food, though! Since they are the same species as the single-headed ones, they often hybridise, and any volunteer seedlings in a neighborhood with a multi-headed one are likely to be more bushy than their known parent. Breeders in the U.S.A. have to go to extreme lengths to keep the single-headed varieties from crossing with the bushy original species, which is a common wildflower in almost all of the states. Occasionally, a seed from even the most reputable supplier will grow to be "wild" in habit.