Looks good !
My ideas:
Rusty root - Tier VI
- Grows slowly, absorbs minor amounts of iron contained in soil
- Drops itself. Can be burned/smelted to get iron dust/piece
- Iron ore needs to be under soil block, needs no light, requires tool to break
- Sharp, Rusty
- Looks like rusty pumpkin stem, damages when breaking with hands
Venomilia - Tier III
- Grows fast, dies in darkness, kills nearby plants
- Whole soil block needs to be replaced to get rid of it
- Grows poison sacks, can be harvested and thrown
- Food, Poison, Persistent
- Walking over it (without boots) applies poison and destroys poison sacks
- Violetish plant with (liquid)poison sacks