Obsolete: This article refers to an aspect of the game which has been removed. It is retained for historical reference only.
Haste Plants is a monsters-only spell that gives all plant holiness monsters within line of sight of the caster haste, decreasing the time it takes them to perform any action by 33%.
Currently, there aren't any monsters able to cast Haste Plants.
Haste Plants was added in 0.13, likely in expectation of the Enchanted Forest branch, but removed when the one monster capable of casting it (spriggan druids) had their spell lists updated.