Wednesday Search Challenge (March 24, 2010): What do you call a rotating flower?

I've probably mentioned that I'm interested in wildflowers.  They're one of the highlights of springtime in Silicon Valley.  Yes, we have tilt-up buildings and endless shopping malls along El Camino Real, but almost everyone also lives within just 5 miles of some kind of open / green space with wildflowers gracing the stage.  Since I grew up in LA, this springtime spectacle still amazes me.


One of the most common wildflowers in the area is mustard, which fills fields to make a brilliant yellow landscape.  Supposedly sown by the Spanish missionaries when they first came to Alta California, they're pretty much ubiquitous.

I was sketching one particular plant last year when I noticed a really odd thing.  I only had a few minutes to sketch, so I did a quick drawing and then left, vowing to return the next day and finish.  But when I came back and sat down, I noticed that the flower stem was in a different position than I'd left it.  It wasn't just pointing a different way, but the flower stem had rotated slightly around it's long axis.  I only noticed this because I went back to draw the same stem / same flower, and found that it had moved with respect to the background.


Huh.


What's going on here?  I got curious about this and started to search for an explanation of this behavior.  (Yeah--think about it.. .this is plant behavior.)  I know that some flowers--sunflowers spring to mind--follow the sun across the sky, but I'd never heard of any flowers rotating on their stem from day-to-day.


The challenge question should be obvious by now... What's this rotating behavior called?  How can I look up more more information about what's really going on?  


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Note for teachers and librarians:  This is a fairly sophisticated question, but representative of the kind of question kids have.  They don't know any of the unique and specific terminology that the biology/botany books would use to describe this, and chances are that you don't know it either.  This is where a little search skill really helps out..