This caterpillar was on the hemizonia. I don't know how much variation there is in the Darker Spotted Straw moth larvae, or if this is another related species. I wasn't prepared to take this one home to rear it out, but I may look for another one like this and do it later.
Also, as you can see, I was holding this caterpillar in my hand when I took the picture. I really don't like seeing my pink, puffy yet wrinkly fingers in my bug photos. So this time, I tried desaturating most of the pink. I think it looks...interesting.