Dendrobium naungmungense (Orchidaceae, Dendrobieae), a new species from Kachin State, Myanmar

Abstract Dendrobium naungmungense, a new species from Naungmung, Kachin State, North Myanmar, is described and illustrated. It is morphologically similar to D. ciliatilabellum and D. vexabile, but the epichile is oblong with three long-ciliate laminae and the column wing has significant denticulation. A preliminary risk-of-extinction assessment shows that the new species should be regarded as Critically Endangered (CR) according to the IUCN Red List Categories and Criteria.


Introduction
The orchid flora of Myanmar is highly diverse but poorly known, as a result of the past political isolation and instability of the country. The remoteness of many orchidrich areas and the difficulties of investigation in rugged terrain have also played a role (Ormerod and Kumar 2003;Kurzweil and Lwin 2014). According to recent estimates, about 800 orchid species are distributed in Myanmar (Kurzweil and Lwin 2014), but this is probably an underestimate. Many new distribution records and new species have been published in the last few years (Ormerod 2002(Ormerod , 2012Ormerod and Kumar 2008;Ormerod and Wood 2010;Nyunt 2006;Kurzweil and Lwin 2012a, b;Tanaka et al. 2011;Tan et al. 2015;Liu et al. 2017;Aung et al. 2017;Yang et al. 2017).
Dendrobium Swartz (1799: 82) (Orchidaceae: Epidendroideae; Dendrobieae) is one of the largest genera of Orchidaceae, with approximately 800-1500 species, which are mainly distributed in diverse habitats in South, East and South-east Asia and Australasia, including the Philippines, Borneo, Australia, New Guinea and New Zealand (Cribb and Govaerts 2005;Wood 2006;Zhu et al. 2009). Around 129 species of Dendrobium have been recorded from Myanmar (Kurzweil and Lwin 2014;Govaerts et al. 2017). During fieldwork in Khakaborazi National Park, Kachin State, Northern Myanmar since 2015, one new species of Dendrobium has been discovered, which is described below. The new species belongs to Dendrobium section Dendrobium Lindl. (Lindley 1844).

Dendrobium naungmungense
Etymology. The new species is named after Naungmung, Kachin State, North of Myanmar, where it was discovered in a vast area of tropical rainforest.

Distribution and habitat.
Dendrobium naungmungense is only known from the type locality. It is epiphytic on the trunk of riparian trees in tropical rainforest, which is dominated by Dipterocarpus obtusifolius Teijsm. ex Miq. (Dipterocarpaceae).
Conservation status. Dendrobium naungmungense was collected in Naungmung Town, Kachin State, Northern Myanmar. Until now, only one population, consisting of ca. 20 mature individuals, has been discovered in 3 years of continuous field investigations (2015)(2016)(2017). In addition, population growth and human activities have led to serious habitat destruction and deforestation in this region. It is also illegally collected by local people due to the highly ornamental and medicinal values. Hence, according to IUCN Red List Categories and Criteria (IUCN Standards and Petitions Subcommittee 2017), D. naungmungense should be regarded as Critically Endangered (CR B1ab (iii, v) + 2ab (iii, v); D), which is the category for species facing the highest risk of extinction in the wild. It meets the IUCN criteria in having an extent of occurrence < 100 km 2 , an area of occupancy < 10 km 2 , is known from a single location and with a continuing decline inferred from the number of mature individuals, a continuing decline in the quality of habitats and a population size of less than 50 mature individuals.

Discussion
Morphologically, D. naungmungenseis is similar to D. vexabile and D. ciliatilabellum, which are characterised by branched stems, short inflorescences with 1 or 2 flowers, lip 3-lobed with a narrow claw and flowers yellowish green, except the lip with purple streaks or spots. However, the new species differs from D. vexabile and D. ciliatilabellum by having a wide mentum, small hypochile, oblong epichile with 3 ciliate laminae and margin crisped with dense hairs and column wing with significant denticulation. Meanwhile, D. ciliatilabellum differs from D. vexabile by having a small mid-lobe, disc of lip with densely long-ciliate laminae and un-reflexed epichile (large mid-lobe, disc of lip with sparsely ciliate lamina and reflexed epichile in D. vexabile) (Seidenfaden 1985, Rao andHaridasan 2005;Liu and Gao 2016).