It is well shaded thus far, although i feel the 'stalk' of the plant is a little jagged (plus fluctuating levels of thickness along the stalk adds to the jaggedness). If the intent was not to make the stalk look smooth, perhaps you could try exageratting the bumps a bit more and have them be more rounded.
The mouth for me is problematic, i can't really see the jaw structure so detail is needed to convey this (Im assuming that will come when you begin to shade the whole head).. Where the jaw and top of the head meet inside the mouth, it is a little too rounded and the it looks like it broke its teeth on a hard rock, try to lengthen/sharpen them a bit.
The right most root seems to have banding going on, fix that.
Heres your plant with indications as to what im talking about.
Blue - Indicates where the stalk fluctuates
Purple - slight banding problem
Yellow - Jaw proposal
Red - Teeth
Sigh.. whenever I try to help someone on here, I always feel like I shouldn't because I am by no means a pro, this is just something I randomly do sometimes (pixel art/spriting that is)...
Anyway I hope I helped, If not beat me with a stick or something
EDIT: Prime example of the jaggedness i speak of, take a look at the left (our left) side just above the lowest blue line...
