This strange fern, previously known as Cyclosorus dicranogramma (v.A.v.R) Ching, is one of the little oddities of the Cameron Highlands, the only location in Peninsular Malaysia from which it has been recorded. Unlike most ferns, whose coiled fronds (crosiers) uncoil upward, this fern’s young fronds frequently have a bend in the stipe, resulting in an inverted structure somewhat resembling a saxophone.

The crosier, with the tightly curled young pinnae, then uncurls in this inverted fashion, somewhat resembling the trunk of an elephant, before finally straightening out into its final, erect form. Throughout its development, the young frond is sheathed in a slimy layer of semi-transparent mucilage. Exuding mucilage was previously thought to be a mechanism to protect developing fronds from excessive moisture loss but is now better understood as a mechanism to facilitate water loss from developing tissues, in place of the transpiration demand that would normally occur in mature fronds, for the continued uptake of water and minerals, from the soil. In the process, however, this layer of mucilage is also acts as a barrier to gas exchange between the fern and the environment.

To overcome this problem, P. callosa develops long aerophores at the base of each developing pinna. These aerophores extend through the mucilage layer to the air outside, enabling the fern to exchange gases with the environment. The aerophores are white when young, giving the crosier the appearance of a coiled millipede, but darken and shrivel as the frond straightens and matures. The only other fern in Peninsular Malaysia with equally prominent aerophores is Plagiogyria tuberculata Copel, also found in the Cameron Highlands, but at higher elevations. Other interesting aspects of this fern include a membranous structure located between adjoining lobes of the pinnae, called a sinus membrane, and relatively large, bright yellow spores.