Beginner Gardening: Tall single-stalk plant with yellow flowers, 1 by thestones15

thestones15 wrote:
I'm new to gardening, and have never used a forum before. I started the garden three summers ago by shaking a can of wildflower seeds around, not realizing the mysteries that awaited me. I didn't notice this guy until it was about 3-4 feet tall, so I don't know what it looks like as a seedling. It was growing amongst a bevy of cornflowers, and I thought it must be a weed since it appeared so quickly and had kind of a spiky topknot. Since I'm new at this, I don't pull anything until I'm positive I don't want it around - which is a good thing. When this plant bloomed, I was fascinated. There's just the one, and if it's not an invasive type of plant, I'd like to add more to the garden. I've managed to identify just about everything that's come up so far, but this one is baffling. Who can help me?