Whether they are spirits trapped on foliage or a species of their own is up to the DM. At first, they appear as vague face-shapes in moss, lilies, decaying hummus, unearthed fungi and so forth. Most of the time they will only animate and speak if spoken to. Whether they can be trusted depends on what the DM needs.
Faceplants make great plot points, clue-droppers and window dressing for an adventure.
UPDATE: Please feel free to contribute to the Gygaxian Anarchy below.
Faceplant detail: These are a form of undead. They either form over a grave, or in an area haunted by the ghost of a druid who died in a natural disaster or from an animal attack. If extant, they are the only manifestation of that undead in the area.
Botch a skateboarding roll, and the DM can give you a clue.
Faceplant says: “Sk8ing can hurt”
Faceplant detail: These are a form of fairie. They claim to be the spirits of lovers who have drowned themselves in a nearby lake. They will try to get players to cross the water, so the water wyrm will drag them under. Then they get a new face they can mimic.