Gymnostomum gracillimum was described by German botanist Christian Gottfried Daniel Nees von Esenbeck and colleagues in 1823 based on a population growing on a slate rock wall near Hüttau in Salzburg, Austria.

In 1846 G. gracillimum was designated a variety of Gymnostomum calcareum by Philipp Bruch and colleagues.

gracile was described by Georg Roth in 1903 based on a specimen collected from Radstädter Tauern Pass, also in Salzburg, Austria.

These names would all be reduced to synonymy with Hymenostylium gracillimum by Heribert Köckinger and Jan Kučera in 2011.

It grows on moist, shaded rocks, and appears to prefer slate, phyllite and schist substrates.