It looks like a dandelion. Sort of.
The leaves are similar. The seed heads (blowheads) are very similar.
The flowers are non-existent, or just something We have never noticed, or it blooms at some odd time.
The biggy though: This sucker is 6 feet tall. Yeah. 6 feet.
Neat plant. We just wish to know what it is.
UPDATE: After some debate on Facebook and Google+, no answer ended up being a slam dunk, but the consensus suggests this is something in the thistle family or in the Cichorieae tribe that includes lettuces, chicory, dandelions and others. I have this sneaking suspicion if I could a couple folks out here to put hands on the plant, they would know it in a heartbeat. Plant identification is so difficult via pictures and drawings.