Epipactis × schmalhausenii K. Richt. (Orchidaceae), a newly identified hybrid in Slovenian flora

Abstract

This study analyzes nine specimens of the genus Epipactis from the Orchidaceae family and classifies them as Epipactis × schmalhausenii K. Richt (Epipactis atrorubens (Hoffm. ex Bernh.) Besser × Epipactis helleborine (L.) Crantz). The work provides the first detailed description of this hybrid in Slovenia. The plants were examined using the hybrid index (HI) method. We analyzed six to ten morphological plant characteristics. In addition to the traits summarized from the literature, two new characteristics related to the proportions of the flower labellum were analyzed from digital photographs and included in the study. Both of these showed high discriminatory power between the parental species. We modified the classical definition of the HI to no longer depend on the number of traits used in the analysis. The adopted trait descriptions of typical parental species were compared to six standard works on Orchidaceae. We did not observe any apparent contradictions, but the descriptions of some characteristics are somewhat inconsistent, which probably indicates their very high intraspecies variability.  A brief assessment of potential geographical, site-related, and temporal barriers to hybridization between the two parental species in Slovenia revealed that none exist. The hybrid is likely quite common in Slovenia and has been overlooked until now, probably due to its substantial phenotypic diversity.