Maximilian sunflower is a perennial sunflower mainly found from Manitoba to Texas but it is also found scattered throughout the tall grass prairie. The flowers run about three inches across but there are a lot of them. They start blooming as early as the first week of September and continue for about 5 weeks. At the peak the top half of the plant is covered with these flowers for about three weeks making a very spectacular display. Naturally the bees love them and monarch butterflys like to stop by them on their way south. Finally the goldfinches feast on the seeds from mid-October to mid-November. These plants are somewhat difficult for squirrels to climb so unlike common sunflowers the birds and not the squirrels get the seeds.
I got the seeds from Park Seed. The package warned of a low germination rate and they were right, perhaps only a third of the seeds sprouted. They grew rapidly, plants started in early March indoors got to 8 feet or more while seeds started later were of course smaller but all of them bloomed the first year. You really need to tie them to a fence or provide some support as strong winds will whip them around and some branches may come off.
After the first year they send up a number of sprouts from the main root, there is little branching on these older plants except at the top (first year plants have branches from top to bottom). The sprouts can be dug up and cut off and placed in new locations. The older plants can look sloppier and strong winds will blow them around. If you want a neater display rip out the old ones every year and replace them with new plants started from seed. Over-watering will also produce excessive growth. I've got a report now from someone who says if you pinch off the growing tips when they are 3-4 feet tall you will get a shorter plant with more flowers. I've got to remember to try that this year.
There is a description of the Maximilian Sunflower on the net from the Native Wildflowers of North Dakota site but be aware that the plant they show there is terribly small and scrawny compared to the well-bred variety from Park's.
Highly recommended if you don't mind tall wild looking things.