Parablechnum gregsonii is a fern with a creeping rhizome and pendent, mostly pinnate fronds 30–80 cm (10–30 in) long.

[2] This species was first formally described in 1915 by William Walter Watts from a specimen collected by "Mr Jesse Gregson...in 1902" and given the name Blechnum capense var.

[3][4] The specific epithet (gregsonii) honours Edward Jesse Gregson who collected the type specimen "on a wet ledge in the face of a perpendicular cliff overlooking a permanent creek in a gully at the base of Green Mountain, a little on the Bell side of Mount Wilson.

[5] In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), this species is placed in the genus Parablechnum.

[6] This fern occurs in the Blue Mountains and ranges of the Illawarra region, where it grows in cool rainforest, often in damp places near waterfalls.