Is it art? Or an accident?

While I was walking near the Farmer's Market in Kerrytown, Ann Arbor, I looked down and saw this.

So, the question is... Is this a piece of artwork or an incredibly beautiful accident? I'm inclined to believe that it is on purpose. 

It is really lovely up close. It's similar to a vine growing up a structure. Or perhaps a spinal chord gone mad? Or how about a replica of a lightning bolt?

In any case, it was a good find. You never know what is out there until to learn to look in unlikely places.