Original Article Orchids on Phu Kradueng’s plateau Purichaya Jongsirikankha 1 , Tosak Seelanan 1* , and Thittasak Suriyachaiwatthana 2,3 1,2 Plants of Thailand Research Unit, Department of Botany, Faculty of Sciences, Chulalongkorn University, Pathum Wan, Bangkok, 10330 Thailand 2 Phu Kradueng National Park, Moo 1, Si Than, Phu Kradueng, Loei, 42180 Thailand 3 Na Yung - Nam Som National Park, Moo 2, Na Yung, Udonthani, 41380 Thailand Received: 11 May 2016; Revised: 6 July 2016; Accepted: 8 July 2016 Abstract Phu Kradueng plateau is the table-top mountain whose altitude ranges from 1,100m to 1,350m and harbors the large area of lower montane coniferous forest and lesser area of lower montane rain forest with many waterfalls. Sporadic floristic exploration has been made for as long as 60 years but no more than 60 species of orchids had ever recorded. Thus, the intensive orchid exploration in Phu Kradueng plateau was conducted from October, 2014 to February, 2016. Together with herbarium specimens and orchid’s census data, it was suggested that as many as 111 species of orchids should have been found on the plateau. Thus far, however, only 78 species had been recorded, and as many as 33 species still have not been seen in this study. Possible causes include illegal smuggling of wild orchids, habitat losses and changes caused by severe wild fires and climate changes. Keywords: orchids, Phu Kradueng National Park, Loei Songklanakarin J. Sci. Technol. 39 (4), 479-487, Jul - Aug. 2017 1. Introduction Orchidaceae is one of two largest families of flowering plants, consisting of about 27,800 accepted species in 736 recognize genera of 5 subfamilies (Chase et al., 2015; The Plant List, 2015). Orchids distribute world-wide except in desserts (Steven, 2016). In Thailand, Chayamarit et al. (2014) enumerated the list of orchids to be 1,169 species. However, since then there had been reports of new species (Gale et al., 2013; Tippayasri & Ngernsaengsaruay, 2012) and new records (Nuammee et al., 2016; Rojchana-umpawan et al., 2014). Many orchids could be found throughout Thailand, though some exhibit restricted range of distribution to certain geographic areas or habitats. Currently, most orchids are disappearing and can only be seen in National Parks, Wildlife Sanctuaries, Forest Parks, and reserved forest. However, the Orchidaceae in the “Flora of Thailand” has not been completed; reports on area-based “catalogs” of orchids still remain largely undone. Thus far, published works were those in Nam Nao National Park (Tokaew & Chantaranothai, 2009) and Phu Ruea National Park (Kongbangkerd, 2007) while many remain unpublished, e.g., Khao Khaio, Khao Yai National Park (Buakhlai, 2005), Thung Salaeng Luang National Park (Phueakkhlai, 2011), and Phu Luang Wildlife Sanctuary (Kasetluksamee, 2014). Surprisingly, despite reports from nearby national parks and sanctuaries, Phu Kradueng National Park remains under-studied for a long time and thus its assessment on orchid diversity is much needed. Phu Kradueng National Park (Figure 1) is located in Loei province in northeastern Thailand. The national park covers the area of 348.12 km 2 , of which 60 km 2 is of heart- shaped plateau top. Geographically, it consists of sandstone, low-altitude mountains surrounding a huge plateau top. The altitude is graduated from 400 to about 1,000 meter and * Corresponding author. Email address: tosak.s@chula.ac.th http://www.sjst.psu.ac.th