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of Triassic Equisetites sp. and
Schizoneura paradoxa, Jurassic Equisetum
columnare and living Equisetum has
allowed the recognition of an evolutionary
series confirming that Calamites and
Equisetum are closely related and belong
to the same lineage. Such a relationship
was previously proposed by Good
[Good, C.W., 1975. Pennsylvanian-age
calamitean cones, elater-bearing spores,
and associated vegetative organs. Palaeontogr.
Abt. B 153, 28–99.] on the basis
of morphological and anatomical similarities.
Indeed, this study clearly shows
that the ultrastructure of the spores of
Triassic and Jurassic Equisetales is intermediate
between that of Carboniferous
Calamites and modern Equisetum,
demonstrating that Equisetum evolved
from Calamites. The present study illustrates
how Calamites spores of the
Calamospora type progressively
evolved into the quite different spores of
living Equisetum. Indeed, it would not
have been possible to understand how
such a transition occurred without this
TEM study. Similarly, it underscores the
proclivity of the Equisetales to develop
unusual structures in both their spores
and their reproductive organs. Moreover,
it demonstrates that the ultrastructural
features of equisetalean spores changed
greatly during their long evolutionary
history, whereas those of other Pteridophytes
groups, such as ferns and lycopsids,
remained unchanged. However, the
most striking outcome of this comparative
TEM study is the demonstration that
spores of the Triassic horsetails show
many ultrastructural similarities with
spores of the Ophioglossaceae, a living
family of primitive ferns. According to
Lugardon and Brousmiche Delcambre
[Lugardon, B., Brousmiche-Delcambre,
C., 1994. Exospore ultrastructure in
Carboniferous sphenopsids. In: Kurmann,
M.H., Doyle, J.A. (Eds.), Ultrastructure
of fossil spores and pollen, pp.
53–66, Royal Botanic Gardens, Kew.],
who made the same observations for the
spores of Calamites, these similarities
indicate that horsetails and ferns are
closely related and have a common origin.
These results are in agreement with
those of a recent DNA analysis which
shows that the horsetails and the ferns
form a monophyletic group of plants.
Moreover, they support and are in
agreement with the phylogenetic analysis
using cladistic principles of Stein et
al. [Stein, W.E., Wight, D.C., Beck,
C.B., 1984. Possible alternatives for the
origin of Sphenopsida. Syst. Bot. 9 (1),
102–118.] which suggests that the
sphenophytes and the ferns as a whole
are descended from a common ancestor,
the Devonian complex Cladoxylopsida
including the Hyeniales. The fact that
the Hyeniales combine sphenophyte and
fern-like features would explain why the
spores of the ferns and those of the ancient
sphenophytes have the same ultrastructural
features. Moreover, this study
indicates that spore ultrastructure retains
ancestral features for a longer time than
the other parts of the plants which
evolve and thus change more rapidly.
This study provides a further demonstration
that spore ultrastructure, particularly
of those preserved in situ, is of great
value in researching the evolutionary
and phylogenetic relationships of plants.
2010010064
现 生 和 化 石 买 麻 藤 孢 子 外 壁 超 微 结 构
和 形 态 的 对 比 = Comparative pollen
morphology and ultrastructure of modern
and fossil gnetophytes. ( 英 文 ). Tekleva
M V; Krassilov V A. Review of Palaeobotany
and Palynology, 2009,
156(1-2): 130-138 2 图 版 .
A considerable disparity of pollen
characters in the modern Gnetales (including
the inaperturate and monosulcate
germination types, the psilate, polyplicate
and spinulose sculptural types)
stands in sharp contrast with their ultrastructural
uniformity. In all of the ultrustructurally
studied living species of
Ephedra, Welwitschia and Gnetum, the
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