Same mystery one I saw in Marin a few weeks ago. It seems to have the tuber-like base to the sporophyte like (I'm told) Phaoceros is supposed to have, but it's definitely way different than the ones without frilly leaves like this.
Hornworts are a group of bryophytes, or non-vascular plants, comprising the division Anthocerotophyta. The common name refers to the elongated horn-like structure, which is the sporophyte. The flattened, green plant body of a hornwort is the gametophyte plant.
