Monotropa callistoma (Ericaceae), a new species based on morphological and molecular evidence from Hunan, China

The subfamily Monotropoideae (Ericaceae) comprises unique non-photosynthetic and mycoheterotrophic plants. Their extensive morphological reduction often poses significant challenges for species delimitation. In this study, we investigated an unknown Monotropa taxon collected from Hunan Province, China, through an integrative approach combining detailed morphological observation and phylogenetic analysis. We sequenced it, assembled the complete plastid genome and reconstructed phylogenetic trees using both chloroplast genomes and the nrITS region. Morphologically, this new entity is readily distinguished from its congener, Monotropa uniflora, by several key characteristics: 4-5 glabrous petals apically one-quarter orange and basally three-quarters white, 8-10 stamens with glabrous filaments, a nodding berry at maturity and a distinctly earlier flowering period (March-June vs. June-October). Phylogenetic reconstructions, based on both chloroplast genomes and nrITS data, consistently resolved this unknown taxon as a distinct lineage, clearly separating it from M. uniflora with strong support. Integrating evidence from morphology, phylogeny and phenology, we hereby describe it as a new species, Monotropa callistoma.