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.