This is the largest tree frog native to the United States (Bartlett 1999). It is also the largest species in the genus (Duellman 1970). Males are about 76 mm and females reach a maximum of 90 mm. Chubby, stocky and short-legged (Savage 2002). Broad, flat head, indistinct from body. It is distinguished from other species by having a row of warts along the lower arm. Snout is rounded in dorsal view and bluntly truncate in lateral view. Large prominent eyes with horizontally ellipted pupils, and gold or silver irises. Distinct tympanum with a diameter about two-thirds of the eye. Dorsal skin is smooth and venter skin is granular (Lee 2000). Varies in color and pattern. The upper surface of S. baudinii can be a shade of green, tan or brown with a pattern of dark patches. Metachrosis is extreme and individuals can change colors depending on circumstances (although individuals tend to retain their dark blotches usually outlined by black) (Savage 2002). The vocal sac of breeding males is grey (Leenders 2001). Males have dark throats and females have light throats (Bartlett 1999). The undersurfaces are white to creamy yellow, usually devoid of markings (Lee 2000). A dark streak extends from the eye onto the shoulder region. There is also a vertical black bar that lies on the upper lip directly below the eye (Norman 1998). Similar to S. phaeota, the dorsal surface of the hind limbs have dark transverse bars (Leenders 2001). Has contrasting yellow and black mottling on the back of the thighs and especially in groin region (Norman 1998). Moderately large appendages. Toes are extensively webbed. Fingers are extensively webbed at bases (Savage 2002).
A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).