SORIA, AUDE1*, BRIGITTE MEYER-BERTHAUD1, and STEPHEN E. SCHECKLER2. 1Paleobotanique, Universite Montpellier 2, Place Bataillon, 34095 Montpellier cedex 5, France; 2Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 - 0406. - Development and architecture of a gondwanan representative of the late Devonian genus Pietzschia (Cladoxylopsida).
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