I've been watching this sunflower--growing just up the street--since it was a wee seedling. The people who live in the nearest house plant sunflowers along their fence every year; I think the wind must have caught one of the seeds and deposited it perfectly in a crack in the sidewalk. I kept expecting it to get run over or pulled, but it's still pushing up nicely. It's almost as tall as me!
(Update 8/18/06: Of course, I jinxed it. Last night I was driving home and saw that my pluckly volunteer had gotten run over!)