Malagasy/Indo-australo-malesian Phytogeographic Connections
Home | Introduction | Gondwanan Relicts | "Lemurian Stepping Stones"
Long Distance Dispersal | Conclusion | References
As a former piece of the African continent that has remained
in close proximity throughout its evolutionary history,
Madagascar would reasonably be expected to possess a biota whose
closest affinities are African. Recognition therefore of
phytogeographic connections with floras far to the east has
attracted the interest of botanists since the classic work of
Perrier de la Bâthie (1936).
Subsequent workers have adopted and
refined the characterization of floristic affinities by
percentage generic overlap within arbitrarily delimited
geographic units ("elements"), among which "Asian", "oriental",
"paleotropical", and "austral" have been utilized to reflect the
eastern affinities (Humbert 1959;
Koechlin et al. 1972;
Dejardin et al. 1973).
However, as Leroy (1978) correctly pointed out,
such analyses of relationship depend upon taxonomic
circumscription of genera rather than phylogenetic hypotheses,
and fail to address process in historical biogeography. The
distinction made by
Aubréville (1976) between "Australo-Papoue"
as Gondwanan elements and "Asiatico-Malesienne" as Laurasian
elements set the stage for a more explicit discussion of the
historical patterns leading to modern-day relationships between
the floras of Madagascar and Indo-australo-malesia. In that
context, utilizing data from recent phylogenetic, paleobotanical,
and paleogeographic studies, I would like to illuminate further
what I believe to be the three major modes of
dispersal/vicariance between Madagascar and lands to the east: 1)
Cretaceous Gondwanan Relicts; 2) Eocene-Oligocene "Lemurian
Stepping-stones"; and 3) Long Distance Dispersal (LDD).
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