| Despite, or
perhaps because of (Patterson 1981), an
excellent fossil record, the
relationships of the conifers to other
seed plants are still not entirely clear.
Whilst conifers have usually been
accepted as a monophyletic group
(Chaw et al. 1997; Stefanovíc
et al. 1998), some recent
phylogenetic studies have suggested that
extant conifers are paraphyletic, with
the Gnetales as sister to Pinus L.
(Bowe, Coat & dePamphilis 2000).
This result appears to be especially
strongly supported by mitochondrial and
chloroplast sequences (Chaw et al.
2000). However, in the absence of
any morphological evidence for such a
relationship, and with the great depth of
branching events within the gymnosperms
(>300 Ma), other workers (e.g. Graham,
S. W. et al. 2002) have suggested
that conifer paraphyly is a statistical
artefact of long branch attraction sensu
Felsenstein (1978). Graham et
al. considered that substitutions are
unlikely to provide useful phylogenetic
resolution in such an ancient group, and
instead sought evidence of major genomic
rearrangements to support hypotheses of
phylogenetic relationships (Graham, S. W.
et al. 2002). Within the
conifers, evidence is growing for a
sister-group relationship between the
Araucariaceae and a clade consisting of
the Podocarpaceae and the Phyllocladaceae
(Chaw et al. 1997; Stefanovíc
et al. 1998; Chaw et al.
2000). Recently, Graham et al.
(2002) reported that a unique
triplication of the rps7 gene on
the chloroplast genome defines a clade
containing all members of the
Podocarpaceae (including Phyllocladaceae)
and Araucariaceae. This group of
families is often referred to as the
‘southern conifers’ (e.g.
Enright & Hill 1995; Enright &
Ogden 1995; Hill & Brodribb 1999).
Within the
Araucariaceae itself, phylogenetic
relationships are not at well understood.
Different studies of different genes have
resolved different relationships between
the three genera Wollemia, Agathis
and Araucaria (including Eutassa
Salisb. sensu de Laubenfels
(2002)) (Gilmore & Hill 1997;
Setoguchi et al. 1998; Codrington
et al. 2002), although all studies to
date have supported the monophyly of each
of the larger genera. Setoguchi et
al. (1998) provided the most
comprehensive treatment so far of the
phylogeny of the family, based on the rbcL
gene, but their tree is poorly resolved,
and much of the phylogenetic structure
within Agathis is poorly
supported, with almost all of it
collapsing in the strict consensus tree.
Additionally, many of the taxa in their
study cannot be identified confidently as
the voucher material they cite is of
uncertain provenance or dubious
geographical locality. However,
their study does show support for
Jaffré’s (1995) hypothesis that the
diversity of the Araucariaceae in New
Caledonia is the result of rapid
post-Eocene speciation of
neo-endemic lineages, rather than the
persistence of relictual palaeo-endemics.
Recent efforts at
a phylogeny of Agathis have not
sampled densely among the Malesian
species (Ryan & Whiffin 2002). Beyond
increased support for the Jaffré
hypothesis of the monophyly of the New
Caledonian species of Agathis
(Ryan & Whiffin 2002), contrary to
the taxonomic schemes of Page and
Whitmore (Page 1980; Whitmore 1980;
Whitmore & Page 1980) and de
Laubenfels (1988), no study has yet
recovered robust phylogenetic structure
within the genus: indeed, within both the
New Caledonian species of Araucaria
and the genus Agathis there is
remarkably little genetic differentiation
in the rbcL gene (Setoguchi et
al. 1998), although for one
Australian species of Araucaria
the 18S rRNA sequence, highly conserved
in many eukaryotes, provides a useful
marker for population level studies
(Graham, G. C. et al. 1996).
Almost all the
phylogenetic studies that have so far
been carried out on Agathis sequence
data have been conducted using only a
single specimen for each species
examined, with the notable exception of
that of Ryan & Whiffin (2002). Consequently,
there has been very little examination of
the issue of paraphyletic species (sensu
Crisp & Chandler 1996) in the genus
or the possible polyphyly of some of the
questionably distinct montane species of
Western Malesia (Waters & Farjon
2002). Ryan & Whiffin (2002)
suggested, on the basis of sampling
primarily cultivated material, that Agathis
montana de Laub. was paraphyletic
with respect to Agathis moorei (Lindl.)
Mast. Further phylogenetic studies,
with denser sampling both across the
genus and within species, will be
necessary to address these questions and
understand the relationships of the
Malesian species, as well as Agathis
macrophylla (Lindl.) Mast. and
Agathis silbae de Laub., on
geologically young islands, to those on
the Gondwanan fragments of New Caledonia,
New Zealand, and Queensland, given that
the explanation offered by Whitmore &
Page (1980) lacks evidential support.
References
Bowe, L. M.,
Coat, G. & dePamphilis, C. W. (2000).
Phylogeny of seed plants based on all
three genomic compartments: extant
gymnosperms are monophyletic and
Gnetales' closest relatives are conifers.
Proceedings of the National Academy of
Sciences of the United States of America
97: 4092-4097.
Chaw, S.-M.,
Parkinson, C. L., Cheng, Y., Vincent, T.
M. & Palmer, J. D. (2000). Seed plant
phylogeny inferred from all three plant
genomes: monophyly of extant gymnosperms
and origin of Gnetales from conifers. Proceedings
of the National Academy of Sciences of
the United States of America 97:
4086-4091.
Chaw, S.-M.,
Zharkikh, A., Sung, H.-M., Lau, T. C.
& Li, W.-H. (1997). Molecular
phylogeny of extant gymnosperms and seed
plant evolution: analysis of nuclear 18S
rRNA sequences. Molecular Biology and
Evolution 14: 56-68.
Codrington, T.
A., Scott, L. J., Scott, K. D., Graham,
G. C., Rossetto, M., Ryan, M. C.,
Whiffin, T., Henry, R. J. & Hill, K.
D. (2002). Unresolved phylogenetic
position of Wollemia, Araucaria
and Agathis. In
Bieleski, R. (ed.) Proceedings of the
IDS Araucariaceae Symposium. In
press, Auckland.
Crisp, M. D.
& Chandler, G. T. (1996).
Paraphyletic species. Telopea 6:
813-844.
Enright, N. J.
& Hill, R. S. (eds). (1995). Ecology
of the Southern Conifers. Smithsonian
Institution Press, New York.
Enright, N. J.
& Ogden, J. (1995). The southern
conifers - a synthesis. In
Enright, N. J. & Hill, R. S. (eds). Ecology
of the Southern Conifers. Smithsonian
Institution Press, Washington DC, pp.
271- 287.
Felsenstein, J.
(1978). Cases in which parsimony or
compatibility methods will be positively
misleading. Systematic Zoology 27:
401-410.
Gilmore, S. &
Hill, K. D. (1997). Relationships of the
Wollemi Pine (Wollemia nobilis)
and a molecular phylogeny of the
Araucariaceae. Telopea 7:
275-291.
Graham, G. C.,
Henry, R. J., Godwin, I. D. & Nikles,
D. G. (1996). Phylogenetic position of
hoop pine (Araucaria cunninghamii).
Australian Systematic Botany 9:
893-902.
Graham, S. W.,
Rai, H. S., Reeves, P. A. & Olmstead,
R. G. (2002). Molecular systematics and
chloroplast genome evolution of
Araucariaceae and relatives. In
Bieleski, R. (ed.) Proceedings of the
IDS Araucariaceae Symposium (in
preparation). Auckland, New Zealand.
Hill, R. S. &
Brodribb, T. J. (1999). Southern conifers
in time and space. Australian Journal
of Botany 47: 639-696.
Jaffré, T.
(1995). Distribution & ecology of the
conifers of New Caledonia. In
Enright, N. J. & Hill, R. S. (eds). Ecology
of the Southern Conifers. Smithsonian
Institution Press, Washington DC, pp.
171-196.
de Laubenfels, D.
J. (1988). Araucariaceae. Flora
Malesiana 10: 419-442.
de Laubenfels, D.
J. (2002). New perspectives on the
division of the Araucariaceae. Oral
presentation at International Symposium
on the Araucariaceae, Auckland, New
Zealand, organized by the International
Dendrology Society.
Page, C. N.
(1980). Leaf micromorphology in Agathis
and its taxonomic implications. Plant
Systematics and Evolution 135:
71-79.
Patterson, C.
(1981). Significance of fossils in
determining evolutionary relationships. Annual
Review of Ecology and Systematics 12:
195-223.
Ryan, M. C. &
Whiffin, T. (2002). The molecular
systematics of Agathis. In
Bieleski, R. (ed.) Proceedings of the
IDS Araucariaceae Symposium. In
press, Auckland.
Setoguchi, H.,
Osawa, T. A., Pintaud, J.-C., Jaffré, T.
& Veillon, J.-M. (1998). Phylogenetic
relationships within Araucariaceae based
on rbcL gene sequences. American
Journal of Botany 85:
1507-1516.
Stefanovíc, S.
a., Jager, M., Deutsch, J., Broutin, J.
& Masselot, M. (1998). Phylogenetic
relationships of conifers inferred from
partial 28SrRNA gene sequences. American
Journal of Botany 85: 688-697.
Waters, T. &
Farjon, A. (2002). The dammars of
Malesia: concepts, characters and
distributions. In Bieleski, R.
(ed.) Proceedings of the IDS
Araucariaceae Symposium. In press,
Auckland.
Whitmore, T. C.
(1980). A monograph of Agathis. Plant
Systematics and Evolution 135:
41-69.
Whitmore,
T. C. & Page, C. N. (1980).
Evolutionary implications of the
distribution and ecology of the tropical
conifer Agathis. New
Phytologist 84: 407-416.
|
