Indica leaves are more rigid, its said the far northern/southern early maturing varieties of land races/pure breeds have more rigid leaves. Sativa's on the other hand originating from the equatorial area/tropics have the skinnier longer fingers with close blade formation, hope this helps. The fingers have something to do with collecting water from air im not 100% sure at the moment, just being a parrot as 2 what i read online a while back.