The relationships Cycadales on the basis of their xylotomy, branching and leaf epidermis

Abstract

In the opinion of the author recent Cycadaceae may be looked upon as intermediate forms between Filicinae, Pteridospermae and monocotyledons. Modern paleontologists, as Remy, Leclerq and thers, divide the species of Psilophyta according to the form of their ramification into three groups, called monopodial, dichotomic and verticillate types. Dichotomy is a phyletic feature which may be ascertained from Psilophyta (Asteroxylon) through Cycadaceae till monocotyl plants, e.g., in palms or in Dracaena, Yucca species. Dicotyledonous trees of perfect dichotomic ramification do not exist, this phenomenon occurs only among ferns, Cycadaceae and monocotyledons. Apart from anatomical characteristics, also the epidermis of leaves and especially the form and structures of stomata constitute a proper basis to conclude to certain family relations.