Morphological variability of Helleborines. I. Diagnostic significance of morphological features in Epipactis helleborine (L.) Crantz, Epipactis atrorubens (Hoffm.) Besser and their hybrid, Epipactis ×schmalhausenii Richt. (Orchidaceae, Neottieae)
Acta Societatis Botanicorum Poloniae