Taxonomic placement of Paphiopedilum rungsuriyanum (Cypripedioideae; Orchidaceae) based on morphological, cytological and molecular analyses

Background: Paphiopedilum rungsuriyanum from Northern Laos was discovered and described in 2014. It is characterized by having miniature tessellated leaves, a flower having a helmet shaped lip with a V-shaped neckline, and a semi-lunate, 3-dentate staminode with an umbo. These morphological features distinguish P. rungsuriyanum from the other known sections/subgenera of Paphiopedilum, making it difficult to group with existing infrageneric units. Results: Paphiopedilum rungsuriyanum has chromosome number of 2n = 26. Fluorescence in situ hybridization study demonstrates that there are two 45S rDNA signals in the telomeric region of chromosomes, and more than 20 5S rDNA signals dispersed signals in the pericentromeric and centromeric regions. Phylogenetic analyses based on four nuclear (i.e. ITS, ACO, DEF4 and RAD51) and four plastid (i.e. atpI-atpH, matK, trnS-trnfM and ycf1) gene regions indicate that P. rungsuriyanum is nested in subgenus Paphiopedilum and is a sister to section Paphiopedilum. Conclusions: The results in combination with karyomorphological, rDNA FISH patterns, morphological and phylogenetic analyses suggest a new section Laosianum to accommodate this species in the current sectional circumscription of subgenus Paphiopedilum.