Distribution and habitats of Paphiopedilum Pfitzer (Orchidaceae) known to occur in Bhutan

Paphiopedilum fairrieanum, P. spicerianum, and P. venustum (Orchidaceae: Cypripedioideae) are reported to occur in Bhutan, of which the former is known to be Critically Endangered and the latter two are Endangered.  Based on numerous field trips conducted over the last decade, populations of P. fairrieanum and P. venustum were located in Bhutan.  No individual of P. spicerianum, however, was found despite many search attempts.  Its occurrence in Bhutan may have been originally erroneous.  Based on the accessibility of the habitats, six 10m × 10m quadrats were defined to enumerate the plant species found in the Paphiopedilum habitats.  Vegetation analyses and cluster dendrograms of the plant species composition indicated the presence of three forest types with distinct species compositions.  Paphiopedilum fairrieanum was found growing mainly as a lithophyte on seasonally dry limestone cliffs or on limestone outcrops with a comparatively open forest canopy.  These populations were mostly located on southwest- or northwest-facing slopes with soil pH ranging from 7.1 to 7.8.  Paphiopedilum venustum, in contrast, was a ground-dwelling species restricted to relatively dense forests with soil pH ranging from 7.1 to 7.5.