Does infraspecific taxonomy match species evolutionary history? A phylogeographic study of Arundo formosana (Poaceae)

Taxonomic resolution below the species rank often appears challenging, partly due to the recent decline in the popularity of infraspecific groupings in the evolutionary and conservation sciences. We test an integrative approach for reconstructing evolutionary history by reconciling past infraspecific taxonomy with molecular methods, using the Taiwanese endemic Arundo formosana (Poaceae). Based on 12 morphometric variables, we provide stronger support for the existence of three morphotypes previously described as varieties and then overlooked, with a clear geographical distribution between western, eastern and northern Taiwan. The phylogeographic analysis of five intergenic regions of plastid DNA supports only the eastern and western lineages and their divergence time according to molecular dating coincides with the orogenesis of the latitudinal central mountain range of Taiwan. AFLP (amplified fragment length polymorphism) nuclear fingerprints also support the east-west divergence in A. formosana followed by secondary contacts in the centre of the island, in addition to the monophyly of the northern morphotype nested in the eastern lineage. We suggest an integrative consensus for the taxonomy of A. formosana that demonstrates the pertinence of infraspecific taxa in integrative taxonomy and phylogeography below the species level.