Cladoxylopsida, the most ancient group of ferns s. l. (late Early Devonian - Early Carboniferous) exhibited a variety of growth habit from small forms to trees and possibly lianas. Distinctive characters of these plants include a complex cauline anatomy and the possession of helically arranged leaf-like organs. Architectural traits and growth habit of a new cladoxylalean plant affiliated to the enigmatic genus Pietzschia are reconstructed. Analysis is based on a 40 cm long preserved proximal portion of stem from the Late Devonian (Famennian) of south-eastern Morocco. Anatomically, the axis is characterized by a primary vascular system comprising numerous xylem plates surrounding a large aerenchymatous pith, sclerenchymatous plates alternating with the xylem plates, a sclerenchymatous outer cortex and no secondary tissue. Large, bilaterally symmetrical decurrent bases of lateral organs ensheath the stem. They are supplied by 8-12 vascular traces. Adventitious roots occur at the stem base. The plant is reconstructed as a small, erect, possibly monocaulous form. Lateral organs are arranged according to a near-Fibonacci type of organotaxis and separated by alternating short and long internodes. This specimen represents the first cladoxylopsid occurrence in Africa. It provides a basis for reconstructing a younger member than those reported previously. It will help to better circumscribe vegetative characters of cladoxylopsids used in analysis of fern phylogeny.

Key words: anatomy, architecture, Cladoxylopsida, Devonian, fern, growth habit