Spore morphology in the Dicksoniaceae. II. The genus Cibotium

Abstract

Species of the dicksonioid genus Cibotium occur in the Hawaiian Islands, Central America – Mexico, and Southeast Asia – Western Malaysia. All investigated specimens produce 64-spored sporangia and the sodium hydroxide assay demonstrates a more or less granular perine deposition over the exine in mature or slightly immature spores. This perine form is shared with the other dicksonioid genera Thyrsopteris and Cystodium and with Metaxya and Lophosoria, two genera of problematical affinity which are palynologically more dicksonioid than cyatheoid. The spores of all Cibotium species show some degree of distal ridge development. The least pronounced ridges occur in Central American – Mexican specimens, but most spores from that region have conspicuous distal ridges whose degree of development intergrades with that of Hawaiian material, whereas the greatest degree of distal as well as equatorial ridge development occurs in the species of Southeast Asia – Western Malaysia. Margo development is variable but is also most pronounced in the species in Southeast Asia – Western Malaysia where it is comparable to that of Lophosoria. All investigated specimens show some degree of pitting of the margo, particularly near and parallel to the laesurae. The number of recognized Cibotium species varies considerably with author and the genus as a whole is in need of modern revisionary work.