The evolutionary and systematic significance of hybridization between taxa of Spiranthes (Orchidacea
by Matthew Pace, Kenneth Cameron
The morphologically overlapping and frequently syntopic species of Spiranthes (Orchidaceae) found in the Sierra Nevada of California and Cascade Range of Oregon –S. porrifolia, S. romanzoffiana, and S. stellata– have long been a source of taxonomic confusion. Much of this confusion is attributed to hypothesized hybridization between species, and a lack of agreement concerning the distinctiveness of S. stellata from S. romanzoffiana. We used molecular phylogenetics incorporating low copy nuclear, nuclear ribosomal, and chloroplast DNA sources, in addition to morphological data, to clarify the evolutionary relationships of this complex. Our results indicate that contrary to long held hypotheses, hybridization between S. porrifolia and S. romanzoffiana appears to be rare or absent. Furthermore, a realignment of taxon status is necessary for S. stellata subsp. stellata and S. stellata subsp. perexilis, with subsp. perexilis elevated to full non-hybrid species rank as S. perexilis comb. nov., and subsp. stellata changed to S. ×stellata, indicating its likely recurrent allopolyploid origin between the sister species S. perexilis and S. romanzoffiana. We also describe Spiranthes ×sierrae nothosp. nov., representing rare allopolyploid hybrids between S. perexilis and S. porrifolia, and provide the first pollinator records for S. perexilis and S. ×stellata.