It is found from lowlands to an altitude of 1,195 m (3,920 ft) above sea level and mainly inhabits humid primary forest, but can also occur in disturbed habitats with trees.

[3][4] The specific name, parsonii, was coined in 1824 by Georges Cuvier in honor of British physician James Parsons.

[1][7][8] Adult males typically weigh 500–700 g (18–25 oz), have a casque on the top of their head and ridges running from above the eyes to the nose, forming two warty "horns".

[7][8] There are two recognized subspecies: The widespread nominate subspecies, Calumma p. parsonii, of both lowlands and mid-elevation altitudes, has no dorsal crest (no spines along the back's ridge) and reaches up to 65 cm (26 in) in total length including tail; there are reports of individuals exceeding 80 cm (31 in), but they remain unverified.

At present, most consider them morphs, despite their separate distributions (in parts of the range, exact variant remains to be verified).

[7][8][9] The "orange eye" variant, alternatively known as "white-lipped", is found in lowlands, less than 500 m (1,600 ft) above sea level, from around Toamasina to Mananara and on the island of Nosy Boraha.

[7][14] Males of C. p. cristifer do not occur in several distinct variants; they are overall green or turquoise and typically have a yellow-orange or rusty-orange blotch on their side.

It has a large range covering almost 40,000 km2 (15,000 sq mi) and inhabits several protected areas, but it appears to occur at low densities, although it possibly is partially overlooked due to preference for roosting high in the forest canopy.