In article ,
wrote...

This plant/flower "sprung up" for the first time in my Central
Illinois garden this Spring. It just started blooming this week (June
5th or so). I did some Web searching on it and thought it might be
related to the Evening Primrose family or the Prairie Sundrop, but not
sure cause the specs don't match exactly. There are a lot of little
carpenter-type bees flying around the blooms. The buds, just before
blooming, are reddish (don't match the other Primrose descriptions
I've been reading), but the flowers are bright yellow. Here is a pic
of the plant on my Web site:

http://home.insightbb.com/~minda27/

It does look to be one of the "evening primrose" [genus Oenothera]
group, all right. Not sure which of the many species, but

http://www.shout.net/~jhilty/plant_index.htm

lists three species as Illinois prairie wildflowers:

http://www.shout.net/~jhilty/plantx/cm_primrosex.htm
http://www.shout.net/~jhilty/plantx/ms_primrosex.htm
http://www.shout.net/~jhilty/plantx/pr_sundropsx.htm

http://www.i-a-s.de/IAS/botanik/d51/oenothe.htm
http://botany.cs.tamu.edu/FLORA/imaxxona.htm

but of course there are many others elsewhere and possibly
in cultivation.

cheers