(September) I have a flower which looks very much like a weed. It blooms at about 8:00 PM
and fades away when the sun is up the next morning. The bloom is a yellow one. I
have heard it called a night plant. Can you tell me what it is.
I would suspect you have an evening primrose, one of the Oenothera species. They do have showy yellow flowers which open late in the day and close the next morning. They are a common wildflower, and some species can be a bit weedy. Remember, one mans weed is another mans wildflower!