what causes this

leaves curled under, clawesque

hmmmm, maybe a tiny bit too much Nitrogen ?

leaves curl under when the plants is trying to perspire or "sweat" and are unable to. most likey becasue its overwatered or underwatered. or it could be to humid in the room.

aye most curling is over watering, sometimes excess side lighting can cause this because of light seeking behavior

here ya go man. https://www.rollitup.org/marijuana-plant-problems/150004-plant-moisture-stress-symptoms-solutions.html
i was clueless over the same situation until i came across this by uncle ben. that dude knows his shit! so props to jumboswisher for hitting the nail on the head. cause after reading that and knowing wat i now know because of it i'd have to agree! its a water/moisture issue!

thanks for the response i think it is low humidity.. my humidity is 16 most of the time arrgghhh