Step by step plant
 

Okay, I made some plant step by step - so I could see my work progress and so you guys can show me were I went wrong. Please note that it's a bit different because I saved it to .gif, mainly (or only) with the brown pixels.

1. Basic, rought outline
2. More detailed outline; added some plant parts and roots
3. Basic shading of the plant part
4. More detailed shading
5. Basic shading of the roots, also detailed them more
6. More detailed root shading
7. Adding a simple background
8. Detailing the background

I like it nice

Try using dithering instead of adding more colors (give a bit rougher surface too...) and add more gray to your plant color, it looks radioactive :(
Your outline is good, but the berries need to rounded more.

Edit: also, add a LOT more contrast ;O

Edit II: here, I quickly summed up what I mentioned to give you an example, I also took a step further, making the berry things glow.

You need to define a light source right now it looks to not have one.