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New Zealand present, Pacific present, tropics of the Old World present
Tropics of the Old World, in the Pacific southwards to New Zealand; in all c. 80 spp., the majority Malesian.


Nakai confined the genus to one species, stating "there is no other fern with which it can off er any specific comparison", but there are three species closely allied to the type in Malesia and four more in the Pacific. The distinctive character of this group is the extreme reduction of basal rudimentary pinnae which consist of little more than swollen aerophores which project through the layer of mucilage which covers very young fronds (). Troll described the mucilage-bearing scales of another species (probably P. kerintjiensis) which he mis-named Dryopteris sumatrana v.A.v.R. (); this species has shorter aerophores than P. callosa and quite large reduced basal pinnae. The number, shape and size of such pinnae provide important characters for distinguishing between species, and in some cases there is still not enough information about them.
Pneumatopteris is closely related to Sphaerostephanos but is distinct in the following characters: presence of colourless short capitate hairs in place of spherical sessile glands; limited development of acicular hairs apart from adaxial surface of rachis and costae; pustular appearance of lower surface between veins of dried fronds; broad thin stipe-scales. There are exceptions to some of these, the most notable in Malesia being P. costata and a few allies which do not have a pustular surface when dried. The species with free veins are nearly all in New Guinea. They do not look like a primitive group and may be derived from ancestors with anastomosing veins. P. truncata looks more like a prototype for the genus.


Base chromosome number 36; 7 Malesian spp., including P. costata, diploid (T. G. Walker, unpublished); P. truncata tetraploid in Ceylon and diploid in N. India and Sarawak; P. pennigera (G. Forst.) Holttum tetraploid in New Zealand.


Nakai 1977 – In: Allertonia. p 226
sensu Holttum 1955 – In: Rev. Fl. Mal. p 255
sensu Copel. 1947: Gen. Fil. 135, 140
Holttum 1973 – In: Blumea. p 42
sensu Copel. 1947: Gen. Fil. 135, 140