Platyzoma: a new look at an old link in ferns.

Record of a chromosome number of 2n = 76, unusual for pteridophytes, in Platyzoma microphyllum R. Br. emphasizes other unique features of this monotypic Queensland fern and provides new evidence of its possible relationships. Other characteristics of this plant, which are not known among terrestrial ferns, are incipient heterospory-having two sizes of spores and a dioecious condition of the gametophytes. These and other morphological features show relationships of Platyzoma to members of the Schizaeaceae and Marsileaceae and relationships of these families to the Polypodiaceae, in which it is treated under the subfamily Platyzomatoideae.