Chamaechrista fasciculata or
Photo by me, Principal Park
I first met this plant near Prairie City at the Neal Smith National Wildlife Refuge back around 2001. My family and I invited a homeschool group for a guided nature walk. Since then, I have seen the partridge pea occasionally while out geocaching. It is not a woodland flower, but an open field flower, with a bright yellow flower and a brown center. I can tell that it is a legume by the leaves -- alternate compound, many leaflets. Like other legumes, it adds nitrogen to the soil it grows in.
According to the current Iowa butterfly forecast, we should look at patches of partridge pea for a chance of spotting a little yellow butterfly, Eurema lisa. The partridge pea is its host plant. (See here for more info on Eurema lisa.)
Seeds from the partridge pea look like legumes, and are food for wildlife, which you can see here against my hand for scale. (It was quite windy, so you'll have to excuse any blurriness for all of these photos.) I read here that birds, deer, and field mice will eat them.