Dave, thanks so much for your help! I thought it was something in the Amaranth family but just couldn't seem to find an exact match. I was originally leaning towards Amaranthus hybridus
http://www.missouriplants.com/... but the description doesn't match because like many other Amaranth, that one is said to have hairy stems. The stems and leaves on the plant in my yard are smooth and I did find couple (A. tuberculatus: A. powellii that have smooth leaves and stems but it's difficult to say for sure if mine is either of those.
Again, thanks for your input and confirmation that the plant is in the family Amaranthus.
