Just what is Walchia?
Sternberg created the genus Walchia in 1825. He included every
fossil of this kind in this genus. Many species have been renamed since.
In his monography (1939 - 1945) Florin used the name
Walchia for a form genus of conifers with unknown
cuticle and/or fructifications. The conifers
with known cuticle, and sometimes with known fructifications, were placed
in the new genus Lebachia. But later on the name Lebachia
appeared not to meet the requirements and it was replaced again
(Clement-Westerhof, 1984).
Visscher, Kerp en Clement-Westerhof (1986) distinguish the following
genera:
- Walchia for species with well-known cuticle and
fructifications, which thus can be placed in a natural family.
- Culmitzschia for species with known cuticle but
unknown fructifications.
- Hermitia for the species with both unknown cuticle
and fructifications.
- Ernestiodendron with one species, E. filiciforme, of which
the leaflets are perpendicular to the axis.
Some species, differing too much from Walchia, have been
placed in still another genus.
So this is a complicated situation. It is in most cases very difficult
(and sometimes impossible) to distinguish species and genera of sterile
branchlets. The names of the Walchia-like fossils in the photos therefore
are approximations of the various plant types. |