Darwin's frog is brown or green with a snout-to-vent length of 2.2 to 3.1 cm (0.9 to 1.2 in). The snout is elongated into a fleshy proboscis which gives the head a triangular shape. The limbs are relatively long and slender. The front feet are not webbed, but some of the toes on the back feet usually are. The dorsal surface is either uniform brown, tan, or reddish brown, uniform pale or dark green, or some combination of brown and green with variable patterning. The ventral surface is black and white, with large blotches.