Wood Saplings are smaller, but more aggressive counterparts of the Wood Guardian. Their vaguely humanoid bodies are composed of jagged wood, a hole in its "face" acting as a maw.
Wood Saplings are weaker and slower then their mother vessel, however more volatile. They aren't capable of using the spiked root ability, unlike their more powerful counterpart. Wood Saplings regenerate in mass during battle and can become an annoyance if multiple Saplings attack the protagonist at once. It is typically best to ignore them considering they can easily be outran, and the Wood Saplings are also frequently destroyed by the Wood Guardian.
Same way as the Wood Guardian, the Wood Saplings represents the "wood" element. They, probably, also serve as servants of the Wood Guardian.