Anyone know why I have microscopic stem plants growing on the surface of
one of my planted tanks? I've noticed them before but ignored them.
They are bright green, 3mm tall and tend to clump in groups of three or
four. I thought it was some type of pollen or spores until I looked more
closely.

Here's one stem under 40x magnification:
http://www.ncasali.demon.co.uk/MicroPlant.jpg

They look like miniature Anacharis or Elodea.

Nikki