First off, try to post your art at a not zoomed in level so we can easily see how it would look in the game. Now, if the sprite is going to be in a game you will not want to anti-aliase the edge of the sprite because it will look like this if you change the color of the background. You don't need to add an outline either , if you do outline you could add color to the outline (I think that's what sellout is). For your sprite though I would recommend hue shifts between highlights and shadows. It seems like you tried this for the flower part but on the leafs and roots you should make the highlights shift to a yellower color and the shadows to a purple-y color. Other then that the sprite has a good shape to it I'd say.