ADDITIONAL FOSSILS IN DOMINICAN AMBER GIVE EVIDENCE OF ANTHER ABORTION IN MID-TERTIARY TRICHILIA (MELIACEAE)

2012·2.2 MB·English

by  Kenton L Chambers

DOMINICAN AMBER EVIDENCE
GIVE
ADDITIONAL FOSSILS IN
(MELIACEAE)
ANTHER ABORTION IN MID-TERTIARY TRICHILIA
OF
George
Chambers
O. Poinar,
Kenton Jr.
L.
Journal of the Botanical Research Institute of Texas
6(2)
562
AND METHODS
MATERIALS
Dominican Republic, between
from mines in the Cordillera Septentrional of the the cit-
The originated
fossils
Two ages have been proposed for this amber
differing
and island of Hispaniola.
Puerto Plata Santiago,
ies of
(Cepek in Schlee 1999) and the younger being
45-30 Ma, based on coccoliths
being fossil
deposit the older
&
amber
McPhee Most of the is secondarily depos-
1996).
on (Iturralde-Vinent
20-14 Ma, based foraminifera
Mamey
Group (Draper
Upper Eocene Lower Miocene et al. 1994). The
sandstones of the to
ited in turbiditic
were found during a search of the Poinar amber collection for additional flowers of
specimens described here
numbers D-9-27C, D-9-27D
and
They designated as
are
might those already described.
Meliaceae that relate to
had been
which
A incidentally illustrated
newly described species of Swietenia,
D-9-27E
in this collection.
& Meliaceae flowers in these amber deposits from
of
representative fossil
Poinar also
(Poinar 1999), is
earlier
&
(Chambers Poinar 2012).
Dominican Mid-Tertiary tropical forest
the
RESULTS
and
A shape pubescence
resembles Trichilia glaesaria in the
The illustrated flower, designated (Figs. 1, 2)
first
from
Chambers lobed, strigillose calyx differs that of T. an-
of its calyx and corolla (cf. Fig. 2 in et al. 2011). Its
A
tique which was described as glabrous and rotate. In apical view (Fig. 1), the ovary of flower is well devel-
mm Four anthers can be seen, showing
and the base of the staminal tube.
oped, wide, strigillose, situated at
1
much
which resemble the one
Three have knob-like terminal structures,
extreme
degrees of abortion.
different
A present on one of these (upper left arrow,
short filament
reduced anther seen in A. antiqua (op. cit.. Fig. 5). is
while the fourth remnant is a tiny filament with a mere suggestion of an anther (upper right arrow).
Fig.
1),
On
obscured staminal tube. the evi-
on lobed, partly
the irregularly
Anthers absent other potential sites
are at
might be
shown Chambers
dence from this flower, the filament stubs of T. antiqua in Fig. 3 of et al. (op. cit.)
them removed by an herbivo-
than having earlier
lacking anthers from the beginning, rather
reinterpreted as
with
densely covered
B the adaxial and abaxial sides of the petals are
designated
In the flower (Figs. 3,
4),
The barely
calyx,
which obscures the natural pubescence of these surfaces.
shiny droplets of a glassy deposit,
much in alterMt-
with reduced locules are visible
view anthers
in view, also has this deposit. In lateral (Fig. 3),
The view of is
ing higher and lower notches between acute lobes on the rim of the staminal tube. apical
The stigma ol
which covered with the glassy deposit.
shows approximately 10 anthers, are also
flower
(Fig. 4)
pubescence or
size.
but the ovary too deeply placed to be characterized as to its
the pistil is visible, is
a«
and petals
The third flower, C, is illustrated in lateral view in Figure 5. Its calyx is not in view, its
on petal at
However, the
mostly too darkly stained to show the necessary details for a complete description.
glaesaria
in
can be seen be as was the abaxial petal surface T.
(arrow), the abaxial surface to strigillose,
left
charac-
surface
adaxial
(Chambers et 2011, Figs. and the petal at the right appears to have the papillate
al. 1, 2),
alternating
in
much on rim staminal tube,
At 8 reduced anthers are present the of the
of flower A. least
teristic
Fig. D-
and
higher and lower positions between acute lobes as in flower B, above, in T. glaesaria (op. cit..
C shown,
(not
locules of these anthers appear to be more reduced than in flower B. In an apical view of flower
ovary «s
the
two species,
the ovary is glabrous, unlike that of flower A. It is interesting that in extant Trichilia
198k
but develops pubescence afterward, as does the fruit (Pennington et al. P-
glabrous before fertilization
C
A e
and
i
C Flowers
The intense staining of flower does not allow further details to be observed.
11).
reduction
anther
anther development; however, as noted by an anonymous reviewer, “(t)he range of
greatly in
modem
between the 3 flowers described here could easily be found in a single day species.”
DISCUSSION
published.
had been
The flowers under consideration here were not discovered until our earlier paper
ocean-deposite
are linked through their having been excavated from amber mines in the same
fossils
and Poinar
now As by Poinar
Tertiary strata, uplifted in the Cordillera Central of Hispaniola. discussed
(1^
^
^
1
and Poinar, Fossil 563
Chambers (
What
possible that the described here do not represent contemporaneous species. they illus-
Trichilia fossils
trate is that Trichilia taxa in these forests were diverse in features such as perianth pubescence, pistil pubes-
cence, and especially the nature of anther reduction and loss in pistillate flowers. However, lacking evidence
sampled
relating to staminate flowers or to differences in the vegetative parts and inflorescence structure of the
taxa, we are limited as any broad taxonomic conclusions that might be drawn from the observed variability
to
in be placed on record as part of the history of
pistillate flowers. It is important, nevertheless, that these fossils
floral evolution in the genus, to be considered in possible future discussions of Meliaceae phylogeny.
beyond
The loss and extreme reduction of anthers in flower A, and probably also in Trichilia antiqua goes
,
the description by Pennington of androecia in functionally female flowers. These authors simply
et al. (1981)
^te without pollen ” In
(p. 26) that in Trichilia the “antherodes [are] narrower than anthers, not dehiscing,
view of the review comments quoted above, this may be a generalization that omits a complete description of
anther abortion and loss in modern species. That two of the Dominican fossils display such androecial reduc-
tion might have been expected.
is evidence of occurrence evolution than
its earlier in Trichilia floral
New
As
genus of Meliaceae in the
discussed by Pennington today the largest
et (1981), Trichilia is
al.
World, with ca. 85 species in lowland tropical America as well as ca. 14 species in Africa and 2 in the Indo-
amber
Malesian exceeds our sample of fossils
region. androecium, well
in the
Its floral diversity, particularly
(Pennington Muellner (2006)
et op. on pages 36-226). Respecting the age of Trichilia, et al.
^ al. illustrations
cit.,
evidence from known combined with chloroplast rbcL data, to estimate divergence times
Meliaceae
fossils,
»
and
the family. The DNA cladogram presented by these authors includes a monophyletic clade of Trichilia 1
other members
genera, which is assigned an origin in the Oligocene. Apart from Trichilia, of this clade are to-
and
limited lnto-China, Malesia, Austroasia.
to the Old World from Madagascar, India,
tropics, Africa to
Muellner by
followed dispersal
et al. (2006) propose West Gondwanan Cretaceous origin for the family,
a
**°ss Eurasia and Beringian and North Atlantic land bridges.
between and North America over the
Eurasia
Eurther
land connections
movement hopping and/or direct
from North South America occurred via island
to
uunng
As
noted previously
the sampling of Cedreleae).
Tertiary see also Muellner 2010, with a dense
et
( al.
^Chambers and
et recognized only two sections in Trichilia, Sect. Trichilia
al. Pennington
2011), (1981)
et al.
T* Moschoxyhim emended Moschoxylum, the
placed in the Sect.
C. DC. The discussed here are best
fossils
defimn
g traits of which and completely united filaments.
are the valvate petals

565
ACKNOWLEDGMENTS
We
thank Andrea Muellner and 2 anonymous reviewers for their helpful comments, which improved the con-
and
tent
clarity of our
presentation.
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