Genetic Discrimination of Spiranthes Cernua Species Complex in South Carolina

Abstract

The genus Spiranthes (subfamily Orchidoideae, tribe Cranichideae) has long been taxonomically problematic, and the compilospecies S. cernua especially is perplexing because of hybridization and polymorphism. Several populations of fall-blooming Spiranthes located in upstate South Carolina differ from S. cernua in some morphological features, but the ranges of other candidates in the species complex are more distant (S. ochroleuca—Northeast, S. odorata—Southeast coastal plain). Samples for genetic analysis therefore were collected from these populations and outgroup species to compare with standards of several Spiranthes species. Segments of DNA from the three plant genomes—nuclear, mitochondrial, and chloroplast—were amplified by PCR, sequenced, and then used for phylogenetic reconstruction. Results from the organelle genomes suggest that one of the two suspected S. cernua deviants has more affinity with S. ochroleuca and differs from the other populations, which grouped mainly with S. cernua standards. The conservative nuclear segment shows few intra-generic differences. This pilot survey verifies the southern range extent of some genes of a Spiranthes species. The survey also provides tools for a broader study of the molecular phylogeny of this genus in North America, which will be needed to delimit populations and habitats for future conservation efforts.