A second subspecies, M. pustulatum subsp. howense (Tindale & P.S.Green) Bostock is endemic to Lord Howe Island.
Source:
Entwisle, T.J. (1994). Ferns and allied plants (Psilophyta, Lycopodiophyta, Polypodiophyta). In: Walsh, N.G.; Entwisle, T.J., Flora of Victoria Vol. 2, Ferns and Allied Plants, Conifers and Monocotyledons, pp. 13–111. Inkata Press, Melbourne.
