Plastid phylogenomics shed light on intergeneric relationships and spatiotemporal evolutionary history of Melocanninae (Poaceae: Bambusoideae)

Melocanninae is sister to other subtribes of Paleotropical woody bamboos
with some 90 species mainly concentrated in Asia. However, phylogenetic
relationships within the subtribe are poorly known. Here, we filled the
gaps in complete plastome data of Melocanninae, reconstructed the
phylogeny of Melocanninae, and further estimated divergence time and
ancestral distribution range. Our results showed that the two major
genera, Cephalostachyum and Schizostachyum, were paraphyletic. Species of
Cephalostachyum were resolved in two successive basal clades, while
Annamocalamus was embedded in the Schizostachyum clade. Different plastid
regions provided inconsistent signals for the relationship of Melocanna
and Pseudostachyum. Conservative loci supported a successive divergence
rather than sister relationship between them and the difference may be
caused by long-branch attraction. We infer that Melocanninae originated in
the East Himalaya to northern Myanmar in the early Miocene. Three routes
were revealed in forming its present biogeographic pattern: in situ
diversification on the Asian mainland; dispersing southwest to Sri Lanka
and to the Western Ghats in South India; and spreading southeast to
Malesia and Oceania via the Indo-China Peninsula. The rapid uplift of the
Tibetan Plateau and the intensification of Asian monsoons since the
Miocene and the sea-level-fall events since the late Miocene might be
potential driving forces for diversification of Melocanninae and,
particularly the latter event, for the species radiation of
Schizostachyum.