A tall, unfamiliar, untidy, somewhat grass-like plant shot up quite suddenly on the edge of a small flower bed by our front door. I even wondered briefly if it could be corn, planted from a stray bit of birdseed. Then it formed a narrow flower pod that looked a bit like very small okra, and one day when I was home for lunch I noticed it had opened into a yellow flower rather like a largish, single-layer dandelion. The flower closed again in the afternoon, which seemed like odd behavior -- plenty of flowers close at night, but I hadn't seen one close not long after noon before. Now it has three or four flower heads, each on its own stalk branching from the main stem.
Well, all these clues and a scan of our Wildflowers of Wisconsin book (hey, close enough), quickly led to an identification: Goat's Beard, Tragopogon dubius (great name, especially if dubius means what it sounds like).
Sometimes called Yellow Goatsbeard, this European import looks like a large dandelion and is common along roads and in open fields. Its large yellow flower head, which turns to face the sun, opens only on sunny mornings and closes by noon, which has led to another common name, Johnny-go-to-bed-at-noon (several other plants share this moniker)... The seed head looks like a giant dandelion plume or like an old gray goat's beard..."It sounds as if, if I let this one go to seed, we'll have more in the future. It wouldn't be an unattractive plant in a group near the back of a larger bed, but I don't think it's in the right place where it is now. But I have enjoyed the serendipity of it.
--Stan Tekiela, Wildflowers of Wisconsin field guide (Adventure Publications, 2000).