The plant is described as being translucent, so the victim can be seen inside. But it is described as completely encasing the victim, and is watertight with an AC (for what it's worth at 10) and HPs, so I would not give anyone line of effect to the victim unless they can ignore barriers with their attack or other effect
Of course by 4th level anything at all should be able to crit against that AC and potentially one-shot the plant with the resulting damage so...
If the AC was also set to the caster's class DC I might consider using it but as it is I have a hard time seeing any value in it. It also doesn't cover whether the seed is hidden like a snare, so have fun with table variation on that too
