Spiranthes minamitaniana (Orchidaceae), a new orchid species from Japan based on morphological and phylogenetic data

Abstract

The delimitation of species within the genus Spiranthes (Orchidaceae) is problematic due to the intricate interplay of phenotypic plasticity, ecological variation, and hybridization, making identification that relies solely on morphology inadequate. In light of morphological and phylogenetic data, we have described a self-pollinating species, S. minamitaniana within the Spiranthes sinensis species complex. Spiranthes minamitaniana shares several morphological features with S. hachijoensis, such as glabrous inflorescence rachis, ovaries, and sepals, a degenerated rostellum, pollinia without a viscidium, and papillate lip basal callosities. However, it can be distinguished by several morphological traits, including semicircular, weakly- or non-3-lobed stigma, and more conspicuous anther cap. Although S. minamitaniana is morphologically most similar to S. hachijoensis, phylogenetic analysis strongly suggested that S. minamitaniana has independently acquired a selfing reproductive mode and constitutes a separate genetic cluster from it. As such, this taxon is morphologically and phylogenetically distinct from other closely related species. Consequently, this taxon is morphologically and phylogenetically distinct from other closely related species.