Nice small bug-free game, pun intended ;). I will echo other comments.
- I couldn't really see the theme in play without anything growing or recovering
- Your design choices have limited this game's potential. By having the goal immobile (makes sense for a plant) the optimal strategy will always be to stay close by jumping up and down (like Cedar Cat Studios mentioned) which gets boring fast. Compare this with Cedar Cat Studios's game - their plants moved and you had to collect things as well, which forces you to move around and switch between offense and defense - greatly increasing dynamism. Alternatively, I could see this game concept as top-down 2D and you were a rolling spike ball that had to "charge" enemies at speed to kill them - anything to force you to move around
- The Art is nice, but consider even simple things could have made it pop even more, such as having the face change between spikes and and spikes out