Lupin Leaves Curling. It curls the entire perimeter edge of the leaf and browns it. If it's just a case of underwatering and you manage to catch the problem.
If the curling leaves seem to be concentrated on the south or west side of the tree, then the Leaf curling from insufficient water is a problem that must be dealt with! Succulents are beautiful from their varied colors. Leaves curling inwards is usually a sign of a plant attempting to maximize their exposed surface area to light for photosynthesis.
It shows that the root rot is still in its early stages.
FYI Leaf curling from light is a totally different curl.
Shortly after curling, the leaves will become limp and even wilt. Some leaves on the pure kush plants also curl down on the sides, kind of resembling an upside down canoe. If it's just a case of underwatering and you manage to catch the problem.