Ptisana is a genus of large eusporangiate ferns in the family Marattiaceae (order Marattiales), comprising species that were formerly included in the genus Marattia. The genus was established in 2008 by Andrew G. Murdock on the basis of molecular phylogenetic analysis and morphological evidence. Ptisana can be distinguished from Marattia in the strict sense by the presence of distinct sutures at the point of leaflet attachment, deeply cut synangia, and the absence of labiate sporangial apertures. The basal chromosome number for Ptisana is 2n=78, compared with 2n=80 for Marattia.
Members of Ptisana are generally large ferns, with fronds often reaching 2–3 metres in length, making them among the most impressive ferns in their range. The genus has a palaeotropical distribution, extending from its westernmost limit on Ascension Island eastward through tropical Africa, Asia, and Oceania, as far as the Pacific islands.
The type species is Ptisana salicina (Sm.) Murdock, known as king fern, whose type specimen was collected on Norfolk Island. Ptisana rolandi-principis, a dwarf species endemic to the Plateau de Dogny in New Caledonia, is a notable exception to the genus's otherwise large stature and is critically endangered.
Etymology
The genus name Ptisana is derived from the Latin word for pearl barley, an allusion to the distinctive shape of the synangia (the fused spore-bearing structures) that characterise the genus.
Distribution
Ptisana has a palaeotropical distribution, ranging from Ascension Island in the South Atlantic eastward through tropical Africa, Madagascar, the Seychelles, South Asia, Southeast Asia, Malesia, New Guinea, northern Australia, and numerous Oceanian island groups including the Solomon Islands, Vanuatu, Fiji, Samoa, Tonga, Micronesia, and the South Pacific. The type species, Ptisana salicina, occurs across South Pacific islands including New Guinea.
Taxonomy Notes
Ptisana was segregated from Marattia following the 2008 phylogenetic study by Andrew G. Murdock, which supported the recognition of a distinct group within Marattiaceae based on both molecular and morphological evidence. The genus differs from Marattia sensu stricto in its sutures at leaflet attachment points, deeply cut synangia, absence of labiate sporangial apertures, and a basal chromosome number of 2n=78 (versus 2n=80 in Marattia). GBIF places the genus in order Marattiales, class Polypodiopsida.
Conservation
Ptisana rolandi-principis, a dwarf species endemic to the Plateau de Dogny in New Caledonia, is critically endangered and is the only known exception to the otherwise large growth habit typical of the genus.
