CONCEPTOS SOBRE EVOLUCION DE LA VENACION EN LAS FILICES LEPTOSPORANGIADAS SUPERIORES

Abstract

The concepts on the evolution of two important characters concerning the foliar architecture of the higher Leptosporangiate Ferns, mainly the series Dipteridaceae - Cheiropleuriaceae - Polypo- diaceae and the family Grammitidaceae, are critically analyzed. a) Branching of the fundamental vascular system in the lamina. It is accepted here, in a broad sense, the pinnate plan as originating from the dicotomic, ·following the known telomic' processes; the functional or structural neotenia, the apical ineristem traumas stable in their genetical basis, and the reorientation of the lamina axis, could have originated the few cases of dicotomic organization found in recent forms. Such dicotomies are not considered to be· a retention of a primitive "psilophytoid" character; neither they are used as an argu- · ment to consider a monopodia! plan as being more primitive than the dicotomic during the evolution of these groups. b) Free and anastomosed venation. Although as a general rule the free venation is more primitive than the anastomosed, in: the phyletic series Dipteridaceae - Cheiropleuriaceae - Polypodiaceae there are sufficient evidences to recognize an inversion of the process; this being probably the only case found in the higher Leptosporangiate Ferns. Some proce!'ses which apparently are correlated with foliar area, dimorphism and supply of the sari, as observed in Microgamma (Polypodiaceae), are. mentioned as examples of simplification and reduc- tion of the venation. The nature of the venation in the Gmmmiticlaceae is also briefly analyzed.