[hoppycalif]

When I was growing sword plants they would both send out runners to reproduce and send up those vertical shoots, also to reproduce. I still don't understand why they did that.

 

[hoppycalif]

If it makes it out of the water, it will flower and may produce emersed small plants. If it stays submerged, small submersed plantlets will result.

So, the vertical shoots are the plant's effort to get a flower growing above the water, for sexual reproduction. Failing that, it just switches gears and reproduces without benefit of a partner? That is what appeared to be happening, but none of those vertical shoots ever made it all the way out of the water for me as best I remember.