[1] F. hydropogon was first validly described by English bryologist William Mitten in 1869, placing it in Fissidens sect.

[4][5] F. hydropogon was initially only known from one site, submerged in a river in Pastaza Province, Ecuador at 450 m (1,480 ft) above sea level.

[4][6] In 2008 it was discovered growing on the vegetation of Cuphea bombonasae on the periodically flooded shore of the River Nangaritza, 950 m (3,120 ft) above sea level in Zamora-Chinchipe Province, 500 km (310 mi) southwest of the type location.

The overlapping leaves are lanceolate with bluntly pointed tips, each measuring approximately 2.5 mm (0.098 in) long.

[4] F. hydropogon is listed as critically endangered by the International Union for the Conservation of Nature under criteria B1 and B2c, based on the small area in which it occurs and the decline of its habitat.