Jamieson, Fausset and Brown on Job 8:16

16. before the sun--that is, he (the godless) is green only before the sun rises; but he cannot bear its heat, and withers. So succulent plants like the gourd (Jon 4:7, 8). But the widespreading in the garden does not quite accord with this. Better, "in sunshine"; the sun representing the smiling fortune of the hypocrite, during which he wondrously progresses [Umbreit]. The image is that of weeds growing in rank luxuriance and spreading over even heaps of stones and walls, and then being speedily torn away.