What's the best focal length for flower pictures

Hi Everybody,
What's the best focal length for taking pictures of flowers.
OOPS
I meant, what's the best subject to camera distance for taking pictures of
flowers.

We have to ask the resident expert on perspective. Joelle is the
resident expert in the PSP newsgroup on perspective.

Joelle's pictures show an incredible mastery of achieving a desired depth of
field (aka perspective).
Look at the attached images. Both have flat lighting. Neither have any
artifacts of lighting, placement, backgrounds, etc. to achieve or remove the
sense of depth.

Yet the first image is distinctly three dimensional.
The second image is distinctly two dimensional (oriental style).

It looks like magic to me.
Phil