All Middle to Late Devonian euphyllophytes have metaxylem
characterized by scalariform to oval and circular bordered
pits, and secondary xylem with scalariform and/or oval
to circular (multiseriate, alternate) bordered pits. The lycopsids
( Phytokneme ) have scalariform tracheids in the metaxylem
and secondary xylem. In contrast to all these, the metaxylem of
Franhueberia consists principally of tracheids with circular and
oval bordered pits, although some (at the periphery of the stele)
have scalariform bordered pits with multiaperturate membranes
(P-type). The latter type of pitting also characterizes the secondary
xylem tracheids. Only the scalariform-fi mbrilate tracheids
described in the metaxylem of the stenokolealean Crossia
( Beck and Stein, 1993 ) are somewhat similar to the multiaperturate
scalariform bordered pits of Franhueberia . However,
in Crossia the end-member of the developmental series of metaxylem
tracheid pitting consists of multiseriate round to elliptical
bordered pits with horizontal slit-shaped apertures. Additionally,
the axes of Crossia have mesarch protosteles with characteristic
protoxylem parenchyma strands ( Beck and Stein, 1993 ).