Morphological evolution and molecular phylogenetics of the Merostachys clade (Poaceae: Bambusoideae: Bambuseae: Arthrostylidiinae) based on multi-locus plastid sequences

Merostachys is a Neotropical woody bamboo genus that occurs in the understory and along forest borders. Our taxonomic studies of its species and morphological analyses have allowed us to recognize morphological groups in the genus. Previous molecular analyses, which included relatively few species, supported Merostachys as monophyletic and sister toActinocladum or Athroostachys. We here provide a phylogenetic estimation for Merostachys based on a broader taxon sampling and seven plastid markers (one coding: ndhF 3' end; four intergenic spacers: rps16-trnQ, trnC-rpoB,trnD-trnT and trnT-trnL; and two introns: rpl16 and rps16). We aimed to test the monophyly of the genus, to verify its relationship with other genera of Arthrostylidiinae, mainly Athroostachys and Actinocladum, and to test whether the previously identified morphological groups were congruent with the molecular data. The monophyly of the genus was confirmed, as was its sister relationship with Athroostachys, although alternate hypothesis testing could not reject a sister relationship with Actinocladum. Two well-supported clades in Merostachys were recovered, one of which encompasses a polytomy. These clades did not exhibit consistent morphological synapomorphies and were not congruent with the morphological groups; however, floret surface (shiny vs. dull) was correlated with the two clades. The lack of resolution in Merostachys, as exemplified by the polytomy, can be attributed mainly to incomplete lineage sorting, suggesting a recent radiation in this group.

Automated summary

Merostachys is a Neotropical woody bamboo genus that is confirmed to be monophyletic and sister to Athroostachys based on broader taxon sampling and molecular analyses. However, the relationship with Actinocladum could not be definitively rejected. The lack of resolution in Merostachys is attributed to incomplete lineage sorting, suggesting a recent radiation in this group.