Lots of stems will grow up and out of water that way but without solid roots the stems may not be strong enough to stay vertical. Let me show you the story of this planting spot:
It started as pest-y Riccia that decided to attach on this wood.
And it spread along pretty happily, so I tossed some HC on it.
And then this Lindernia rotundifolia 'Variagated'.
After a little bit, the Lindernia sp. established. Notice it's just on a bed of the Riccia which is on top of the wood.
And now it's weedy and flowering. (Crap cell pic from this morning, early light - no tank lights)
So, yeah, grows well enough that it needs shaping. More attractive and vertical when it grows emergent up out of the water or fully/mostly emersed with more space for strong roots, though. Again, like most stems will branch upwards from nodes after laying down the stem, and how I'd suggest starting it or filling some space with it. Think Bacopa or Rotala-like.