The evolutionary history of sedges (Cyperaceae) in Madagascar

Aim: Madagascar is renowned for its unparalleled biodiversity and
endemism. With many ecosystems under threat, research is urgently needed
on its unique plant diversity. This applies both to Madagascar’s forests
and treeless vegetation types. Sedges (Cyperaceae) are among the top ten
species-richest angiosperm families in Madagascar (310 native species, 38%
endemic), of which two thirds occur in open habitats. We aimed to infer
the evolutionary history of sedges in Madagascar, by estimating the
number, age and origins of endemic lineages, and how they diversified on
the island. We tested contrasting hypotheses of (i) few colonisations but
important in situ radiations against (ii) a high number
of anagenetic colonisations. Location: Madagascar and the
surrounding Indian Ocean islands, integrated within a global dataset.
Taxon: Sedge family Cyperaceae. Methods: We estimated
time-calibrated molecular phylogenies encompassing a large proportion of
Madagascar’s known sedge flora (incl. 55% of native species), integrating
sequence data for 1382 accessions representing almost 25% of the c. 5600
sedge species worldwide, combined with ancestral area reconstruction,
diversification analyses and Bayesian stochastic mapping.
Results: Cyperaceae lineages arrived in Madagascar from c. 40 mya
with many arriving more recently. About 20 endemic lineages of Cyperaceae
occur on the island, of which only six encompass more than five species.
All except one of the endemic lineages that diversified in Madagascar use
the C3 photosynthetic pathway. The main biogeographical links of
Madagascar’s sedge flora are to Southern and Tropical Africa. Main
conclusions: The biogeographical history of Cyperaceae in
Madagascar is a chronicle of relatively recent multiple in and out
processes of long-distance dispersal colonisations constrained by
distance. Also, the Madagascar region is not only a “sink” for immigrant
taxa, in situ diversification and dispersal to other
regions also occurred. Some of the most diverse endemic lineages show
clear adaptation to local environments.