Structure and Organization of the Vascular System in the Rhizome of Drynarioid Ferns

Form and structure of the vascular cylinder of the rhizome of14 species belonging to six genera of drynarioid ferns are described.The study reveals that drynarioid ferns fall into two categories:the Drynaria group (Drynaria, Photinopteris), which is probablythe more primitive, exhibits the alternate two-ranked leaf arrangementand this could have led through suppression to the one-rankedcondition occurring in the Aglaomorpha group (Aglaomorpha, Drynariopsis,Pseudodrynaria, Merinthosorus, Thayeria). It seems that rhizomemorphology provides characters which help to separate differentspecies into the two distinct groups and indicates some phylogenetictrends. The most characteristic feature of the rhizome of drynarioidfern is seen in Thayeria, where some of the leaves on the dorsalsurface of the rhizome are dormant and some of them developon a prominent short, stout phyllopodium. Pteridophyta, Polypodiaceae, rhizome, vascular system, drynarioid ferns