As far as I can tell, this is one single cosmos plant. It will bloom continuously all summer, and into early autumn. And what pretty blooms they are.
I have mostly orange ones, but cosmos comes in all kinds of colors: red, orange, yellow, white, pink, purple...
Most of the orange cosmos I have in the yard this year are from seeds that I collected from last year, or ones that have self-seeded the last two years. I only ever bought one packet of all orange cosmos, three years ago. The seeds are so easy to harvest that I don't see myself ever buying cosmos seeds again. Unless I want a color other than orange.
I did still have one packet in my seed box, that was left over from 2005, of a cosmos mix. It is Burpee's Cosmos Bright Lights Mix. Since it has reds, oranges and yellows, I'm going to try to collect seeds mostly from the patch where I planted these. That way, I'll have more of a variety next year.