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a stem not a leaf, one monocot (an epiphytic orchid) and one species of
Podocarpus
(a conifer). The cuticles were enzymatically isolated; the residue following acid and
base hydrolysis yielded a highly aliphatic signal upon pyrolysis. There are two other
recent reports of cutan: 1. in fruit cuticles of green pepper
Capsicum annuum
(Chefetz
2003
), based on the presence of a residue from enzymatically isolated cuticles sub-
jected to acid and base hydrolysis; 2. in stems of
Arabidopsis
(Xiao et al.
2004
), based
on a nonsaponifi able residue from enzymatically isolated cuticles. The materials were
not analysed chemically. The
Capsicum
example meets the defi nition of cutan as yield-
ing a non-saponifi able and non hydrolysable residue (although confi rmation of the ali-
phatic signal would be preferable). It is not known, however, whether the
Arabidopsis
nonsaponifi able residue contained a highly aliphatic component or was composed
entirely of lignin and polysaccharide moieties derived from the cell wall, which is
clearly evident in the published TEM images of the cuticles (Xiao et al.
2004
: Fig. 7).
Cutan and the Leaf Fossil Record
Cutan occurs in leaves of the living plants
Agave americana
,
Clivia miniata
,
Clusia rosea
and
C. multifl ora
, an unnamed epiphytic orchid,
Cereus
(presumably
stems),
Prunus laurocerasus
(resistance to acid hydrolysis not tested), and one
Podocarpus
species. There is no known fossil record of
Agave
,
Clivia
, epiphytic
orchids, or cacti (e.g. Collinson et al.
1993
; Herendeen and Crane
1995
). Fossil
Clusiaceae are represented in the late Cretaceous (Crepet and Nixon
1998
) but by
fossil fl owers not leaves. There is one record of Clusiaceae leaves, preserved as
impressions (i.e. organic material is absent) from the Tertiary of India (Ambwani
1991
), but their identity is equivocal.
Prunus laurocerasus
has been reported from
the Pliocene and Miocene of continental Europe (as
Laurocerasus
: Palamarev and
Petkova
1987
). However,
Prunus
leaf fossils are generally rare and the rosaceous
subfamily Amygdaloideae (to which
P. laurocerasus
belongs: Lee and Wen
2001
)
is typically represented by fruit stones in Paleogene and younger strata (Mai
1984
).
Podocarpus
leaves and pollen have been recorded from the Cretaceous,
Paleogene, and Neogene of Australia (Hill
1994
,
2004
), although the leaves or
phylloclades of many other Podocarpaceae are usually far more abundant and
more diverse than
Podocarpus
leaves (e.g. Hill
1994
, Table 12.1, p. 284). Although
cutan has been reported in
Podocarpus
(Boom et al.
2005
) it may not be present
in all species (Collinson et al.
1998
).
This study has shown that cutan is absent in the leaves of the living fl owering
plants
Acer campestre
,
Quercus robur
,
Castanea sativa
,
Citrus limon
,
Betula alba
,
Populus hybrida
, and
Gossypium hirsutum
, and the conifers
Pinus sylvestris
,
Metasequoia glyptostroboides
and
Abies grandis
(see Table
2.1
for complete list).
We are not aware of a fossil record for
Citrus
or
Gossypium
leaves (e.g. Collinson
et al.
1993
). Fossil
Castanea
leaves are infrequent but are recorded in the late
Neogene of Europe (Kva
ek and Walther
1989
) and the Oligocene and Neogene of
Japan and China (Tanai
1995
). Fossil
Betula
(Crane
1989
; Walther
1999
; Hably
č
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