Biology Reference
In-Depth Information
(
Pryer et al., 2001
). Using ozonation, acidolysis, infrared spectroscopy and
1
HNMR,
Jin et al. (2005)
reported the presence of S lignin in Selaginella
tamariscina, with an S/G ratio of 1.3. In Selaginella martensii, by means of
nitrobenzene oxidation,
Gross (1980)
detected 44% S units.
G´mez Ros et al.
(2007a)
reported 71% S units in S. martensii fronds, using thioacidolysis, with
an H:G:S ratio of 5:24:71. 2D NMR analysis revealed a 2:22:76 ratio, and a
remarkable distinction between the Selaginella cortex (with S/G of
3.53)
and the xylem (S/G
0.06) (
Fig. 6
).
Syringyl units in Isoetes histrix represented 27% of the total lignin building
blocks, a composition strongly recalling that of angiosperm lignins. The
presence of syringyl units in Isoetes lignin is, however, consistent with the
occurrence of angiosperm-like vessels (
Schneider and Carlquist, 2000
). How-
ever, although I. histrix showed syringyl lignins, this was not the case with
Isoetes fluitans, in which thioacidolysis revealed that lignins are exclusively
constituted by G units (
Espi
˜
eira et al., 2011
). Clearly, the case of Isoetes
illustrates that the evolutionary gain of syringyl lignins is far from being
understood, at least according to the current models for lignin evolution.
3. Euphyllophytes
Living euphyllophytes belong to two major clades: the seed plants (sperma-
tophytes) and a clade that includes several 'fern' lineages, the horsetails and
the whisk ferns (monilophytes) (
Pryer et al., 2004b; Rothwell and Nixon,
2006
). The monilophytes include five major lineages: leptosporangiate ferns,
Marattiales, Ophioglossales, Psilotales and equisetophytes. The common
name 'fern' is applied to the members of Leptosporangiatae, Marattiales
and Ophioglossales (the last two constitute the so-called eusporangiate ferns;
Judd et al., 2008
). Leptosporangiatae represent more than 12,000 living
species, whereas Marattiales represent 150 living species, mainly plants of
the wet tropics. The Ophioglossales contain 80 species, Psilotales include
about 15 species, as well as equisetophytes (horsetails;
Judd et al., 2008
).
Horsetails were present in the Devonian period but became much more
abundant and diverse in the Carboniferous period, when some of them
became impressive trees. The position of equisetophytes within the monilo-
phytes remains uncertain (
Pryer et al., 2004a
).
a. Ferns. Ferns are a monophyletic group, which include 300 genera and
9000 species ranging in size from a few centimetre to 20 m tall (
Judd et al.,
2008
). Ferns are widespread, especially in temperate regions and the tropics.
Monilophytes can be terrestrial, epiphytic or aquatic.
There are few data available concerning pteridophyte lignin, but the
presence of guaiacyl units has been confirmed in several ferns, such as
