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The arborescent habit in the
Cladoxylopsida
Morphology of pseudosporochnalean trees
The Pseudosporochnales currently include four
genera based on both vegetative and fertile material:
Calamophyton, Pseudosporochnus, Wattieza and
Lorophyton (Berry & Fairon-Demaret 2002)
(Fig. 2). Although somewhat more accurate, the
reconstruction of Calamophyton presented by
Schweitzer (1973) has never been as popular as
the amazing reconstruction of Pseudosporochnus
elaborated by Leclercq & Banks (1962) and repro-
duced in many textbooks (Lemoigne 1988;
Stewart & Rothwell 1993; Taylor & Taylor 1993).
Evidence for the new reconstruction of Pseudos-
porochnus proposed by Berry & Fairon-Demaret
(2002) comprises isolated pieces of trunks and
branches of P. nodosus collected by Leclercq
herself in the 1950s. The plant that these two
authors reconstructed as a 3 m high tree is presumed
to be a small representative of the genus. The taper-
ing trunk measuring about 10 cm proximally and
6 cm distally bears densely inserted lateral branches
that are shed as the tree grows. The younger
branches, representing the photosynthetic modules
of the tree, form a distal crown. Berry & Fairon-
Demaret (2002) hypothesized that the basalmost
part of the trunk in Pseudosporochnus was
swollen based on the occurrence of bulbous bases
in Bohemian specimens of P. verticillatus. This
feature is known in two other pseudosporochnalean
genera: Lorophyton and Calamophyton.InLorophy-
ton, roots radiate from the base (Fairon-Demaret &
Li 1993). The recent reconstruction of the Gilboa
trees whose crowns are referrable to Wattieza
and swollen bases to Eospermatopteris (Fig. 3c)
strengthens the concept of a pseudosporochnalean
bauplan similar to Berry and Fairon-Demaret's
model of Pseudosporochnus (Fig. 5a). It also
shows that such trees may have exceeded 8 m in
The Cladoxylopsida evolved in the Early Devonian,
were especially abundant and diversified in the
Middle Devonian and became extinct in the Missis-
sippian (Fig. 2). Morphologically, the Cladoxylop-
sida comprise several orders of branches but lack
leaves, that is, determinate organs that are both two-
dimensional (2D) and with a photosynthetic lamina
(Fig. 3a, b). The derived character shared by all
members of the group is anatomical. It consists
of a highly dissected vascular system, the most
complex known among plants of this age (Fig. 3d,
f, g). One question about this innovation is how
this character may have been linked to the diversifi-
cation of growth forms in the class and especially to
the evolution of the pseudosporochnalean trees, the
tallest plants of the Middle Devonian.
In recent years, a large amount of morpholo-
gical information briefly reviewed below has been
accumulating on the Pseudosporochnales. This
information has significantly increased our knowl-
edge on how trees in this group may have looked
like externally, in what habitat they grew and what
kind of forests they may have formed. The structure
and growth potential of their root system remains
uncertain however, and information on the internal
anatomy of the stem is still scarce (Leclercq &
Lele 1968). Here, we propose a growth model
integrating this information on the Pseudosporoch-
nales together with the anatomical data we have
accumulated in the past years on Pietzschia, a non-
pseudosporochnalean genus that evolved large-
sized plants in the Late Devonian. We hypothesize
that this model is applicable to a large range of Cla-
doxylopsida showing an erect habit. It may be used
in further studies to estimate the amount of lignous
tissues produced by pseudosporochnalean trees.
MISSISSIPPIAN
Emsian
Eifelian Givetian
Frasnian
Famennian
Tournaisian
Calamophyto n
Pseudosp orochnus
Foo zia
Wattiez a
Lor op hyton
Xenocladia
Cladoxylon
Pietzschia
Fig. 2. Stratigraphical distribution of the cladoxylopsid genera mentioned in the text. Pseudosporochnales in grey box.
(Adapted from Lemoigne & Iurina 1983; Gerrienne 1992; Fairon-Demaret & Li 1993; Berry 2000; Edwards et al. 2000;
Meyer-Berthaud et al. 2004; Soria & Meyer-Berthaud 2004; Cordi & Stein 2005.)
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