A.T. Robertson Commentary Matthew 13:6

"and when the sun was risen, they were scorched; and because they had no root, they withered away." — Matthew 13:6 (ASV)

The sun was risen (ηλιου ανατειλαντος). Genitive absolute. "The sun having sprung up" also, same verb except the absence of εξ (ανατελλω, εξανατελλω).