I have been noticing these plants for the past few years and it always seems weird to me to associate Sunflowers with December. Gigantic Sunflower Shrubs, at that. I also assumed incorrectly they were some sort of Helianthus. Not the case, this is a Tithonia, Tithonia diversifolia – the Bolivian Sunflower. In another perversity of plant naming, the Bolivian Sunflower is native to Mexico and Central America. I am fairly certain Bolivia is in South America. This could be explained by the fact that the name Mexican Sunflower is already taken from a small perennial, another Tithonia.
A neighbor has a hedge of Bolivian Sunflowers screening the backyard. This Sunflower hedge is at least 12 feet tall and in full bloom right now. This plant grows foliage Spring and Summer and flowers through most of the Fall and Winter. It has just really started blooming in earnest and should continue for a couple of months. Another one of those kooky benefits of living in South Florida, Sunflowers all winter.
As this plant has the potential of attaining a height of 16 feet and bears 6″ flowers profusely, I imagine it can put out quite a few seeds and offspring could become a problem. I am not sure I would try planting a hedge, but maybe installing one or two to screen a view where the lawnmower will run over any nearby seedlings. One has to practice selective lawn mower placement of plants in South Florida, if there is any question of overabundance. No winter frost has meant nothing ever dies. Or anything you want gone refuses to die.