Phylogenetic and morphological data support a new combination for a grass endemic to Madagascar and nearby islands: Trichanthecium ambositrense (Poaceae)

Backgrounds and aims – Trichanthecium is a grass genus composed of species transferred from Panicum and is positioned in an incertae sedis clade in the tribe Paniceae (“ Sacciolepis grex ” clade), formed exclusively by C 3 taxa. Currently, the genus possesses 52 species occurring in tropical and subtropical America, Africa, and Madagascar. Trichanthecium perrieri is the only species endemic to Madagascar and is morphologically related to another endemic species: Panicum ambositrense.

We evaluated the position of P. ambositrense in the “ Sacciolepis grex ” clade, and applied an integrative approach, combining phylogenetic, anatomical, and morphological analyses to assess whether the species belongs to Trichanthecium. Material and methods – The phylogenetic analyses were conducted using previously published plastid markers (ndhF and rbcL). Anatomical analysis was used to describe the cross-sectional and epidermal leaf anatomy, and the taxonomic treatment was based on herbarium material, focusing on the macromorphological description of the species, micromorphological description of the upper anthecium (with scanning electron microscopy), and taxonomic comparative comments to other species.

Key results – The phylogenetic analyses confirmed the position of P. ambositrense within the Trichanthecium clade, in a group with T. aequinerve and T. perrieri. Anatomical analysis indicated that the species has C 3 photosynthesis, based on the presence of two sheaths without specialized chloroplasts surrounding the vascular bundles and six to ten mesophylls cells with specialized chloroplasts between consecutive vascular bundles.

The taxonomic analysis indicated that P. ambositrense matches the morphological concept of Trichanthecium. Conclusion – A new combination, Trichanthecium ambositrense, is presented along with its morphological description, a distribution map, an illustration, data on its distribution, habitat and phenology, a preliminary conservation status assessment (Vulnerable), and taxonomic comments on related species. The species of Trichanthecium occurring in Madagascar are listed and discussed, and an updated identification key is presented for the Old World species of the genus.