www.runtimedna.com/forum/downloads.php  morphing rose  - Free

There have been a few others but I can't remember where they were.  If I remember I will let you know.  Other wise, I suggest searching the Free Stuff and google.

Daz3D and RDNA both have a fairly large number of flowers and other plants for sell.  There are a few here as well.

Poser Pro 2010