Revue internationale d'écologie méditerranéenne International ...

Phylogenetic relationships and infrageneric classification of Astragalus tragacantha L. (Fabaceae), inferred from nuclear ribosomal
DNA Internal transcribed spacers data (nrDNA ITS)
nial herb widely spread in Eurasia, takes an
obvious basal place, while Astragalus depressus,
an astragal confined on mountains around
Mediterranean Basin, is located between
clade 2 and the base of the MP tree, supported
by a poor bootstrap value.
Homoplasy of thorny cushion-form
in Mediterranean Astragals
The NJ phylogeny positions the West Mediterranean
Astragalus tragacantha in clade C
(Figure 1), clearly separated from clade D
which includes most of the thorny astragals
(such as all sampled astragals of subgenus Tragacantha
and some species of other subgenera).
In fact, recently, morphological (Zarre &
Podlech 1997) and then molecular analyses
(Kazempour Osaloo et al. 2003) have allowed
gathering many spiny astragals, previously
separated in different subgenera. But the
absence of A. tragacantha in clade D is an evidence
of homoplasy for this character. The
thorny cushion-forming is an adapted structure
to aridity and strong winds of North-West
Mediterranean coasts but also of Mediterranean
mountains. This form exists in other
astragals of the same section (Tragacantha DC
of subgenus Cercidothrix Bunge) as A. genargenteus,
A. gennarii, A. greuteri and A. sirinicus
which are West Mediterranean orophytes
and A. angustifolius, a South-East European
orophyte (Baccheta & Brullo 2006), but none
of these orophytes have been sequenced for
nrDNA ITS. Their geographic proximity, their
morphological similarities and their belonging
to section Tragacantha are serious points
underlining their probable close phylogenetic
relationship with A. tragacantha. Knowing
that South-Western and Sino-Himalayan
regions of Asia are supposed to be the geographic
origin of Astragalus genus, a scenario
of differentiation from Eastern to Western
Europe can be assumed (Nimis 1981).
Based on these observations, no decisive conclusions
can be proposed on Astragalus tragacantha
history or homology with its closest
relatives. In order to set robust hypothesis
about evolution and history of Astragalus tragacantha,
more taxa from clade C (Figure 1)
must be sampled. Further steps of sampling
should focus on other species of section Tragacantha
as A. balearicus, A. genargenteus,
A. sirinicus, A. gennarii, A. greuteri and A.
angustifolius.
ecologia mediterranea – Vol. 36 (1) – 2010
Acknowledgments
The authors thank Martin Wojciechowski for
answering to our questions on a genus widely
studied by his works, Pr Akhani to have provided
us study elements about Astragalus, the
Corsican Environment Office to have allowed
us to sample in Corsica, and the Marseille
municipality which grant funds to this study.
Lastly, the authors would like to acknowledge
the anonymous reviewer of this publication
and Dr Ong’amo for helpful comments on the
manuscript.
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