Phylogenomic insights into species boundaries and relationships in Malagasy Bulbostylis (Abildgaardieae, Cyperaceae) using Angiosperms353 target sequencing

Abstract Species delimitation based only on morphological characters can be challenging in groups where morphology is highly variable or difficult to study. In such cases, molecular data may be used to test the robustness of morphology-based taxonomic treatments. In Cyperaceae, phylogenomic studies have helped clarify relationships and taxon delimitation at the genus level and above, but species delimitations and relationships remain poorly documented in many genera, notably Bulbostylis (hairsedges). Bulbostylis is a morphologically diverse and taxonomically complex group, with Madagascar representing one of its centres of endemism. Species delimitation within the genus has long been hindered by the scarcity of stable diagnostic characters and the absence of molecular data. To evaluate whether the Malagasy Bulbostylis species correspond to distinct evolutionary lineages, we sequenced 353 nuclear loci (Angiosperms353) from 102 specimens collected between 1805 and 2023, including herbarium and silica-dried material. After removing samples with low sequencing success, 64 accessions representing 25 species were retained. Target sequence capture data were analysed using standard phylogenomic approaches, including sequence alignment, maximum likelihood gene tree inference, and species tree inferences using maximum likelihood and multispecies coalescent summary approaches. Phylogenetic analyses recovered 13 well-supported clades corresponding to taxa currently recognised based on morphological characters ( B. andringitrensis , B. barbata , B. erectopallescens , B. festucoides subsp. bathiei , B. filamentosa , B. firingalavensis , B. hispidula , B. mahafalensis , B. micranthera , B. renschii , B. schoenoides , B. tristicha , B. viguieri ), and highlighted a possible case of budding speciation with B. trichobasis being nested inside B. andringitrensis in the species trees. Potentially undescribed taxa closely related to B. flaccidula and B. pseudocollina were identified, while another ten species will require further investigation due to low or no data availability. Additional field collection of fresh material, together with sequencing and analysis of other herbarium specimens, will be necessary to fully understand species delimitations in these lineages. These results indirectly show that morphological characters such as inflorescence architecture, glume morphology, leaf sheath, and nutlet features remain highly reliable for species identification in Malagasy Bulbostylis .