Wednesday, June 8, 2016

[Botany • 2016] Cleisostoma yersinii • A New Species of Cleisostoma (Orchidaceae) from the Hon Ba Nature Reserve in Vietnam: A Multidisciplinary Assessment

Cleisostoma yersinii  
 J. Ponert & Vuong 

DOI: 10.1371/journal.pone.0150631


A new species, Cleisostoma yersinii J. Ponert & Vuong, is described and illustrated based on the material collected in the Hon Ba Nature Reserve in southern Vietnam. In addition to conventional (macro)morphological examination we comparatively investigated root and leaf anatomy (using light and fluorescent microscopy), assessed nectar characteristics (using HPLC analysis), determined nuclear genome size (using DNA flow cytometry) and reconstructed phylogenetic relationships (using nrITS sequences). Cleisostoma yersinii differs from its putative closest relative C. birmanicum in wider and shorter leaves, larger flowers, distinct lip with S-shaped tip of the mid-lobe, and a shallow spur with two large nectar sacks separated by prominent calli and septum. Nectar is sucrose-dominant and very rich in sugars. Stomata are developed on both sides of the leaf and have prominent hyperstomatal chambers and substomatal cavities. Roots with well-developed exodermis and tracheoidal idioblasts are covered by a two-layer Vanda-type velamen. Chloroplasts occur not only in the cortex but are also abundant in the stele. Mean 1C-value was estimated to 2.57 pg DNA. An updated identification key is provided for SE Asian sections and all Vietnamese species of Cleisostoma.

Fig 4.  Cleisostoma yersinii   J. Ponert & Vuong 
(A) Habit. (B) Inflorescence. (C) Flower from the front. (D) Flower from the side. (E) Column from the front. (F) Peduncle. (G) Ovary. (H) Column with a removed cap. (I) Pollinarium on the column with a removed cap. (J) Papillate surfaces of lip calluses. (K) Tip of the lip with a single tail (arista).
  Scale bars: C, D, F, G– 1 cm; E, H, I, J, K– 1 mm. A specimen cultivated in the Prague Botanical Garden collected as holotype. Photo J. Ponert.   DOI: 10.1371/journal.pone.0150631  

Etymology: The species is named after Alexandre Emile Jean Yersin (1863–1943), a Swiss-French physician and bacteriologist who significantly contributed to the exploration of the Hon Ba mountain area.

Ecology: Several plants of C. yersinii were found growing as terrestrial on bare mineral soil exposed by road building (Figs 1 and 2). However, their roots spread along the ground surface and did not penetrate into the soil. The ground was only sparsely covered by lichens and mosses, and the growing conditions of C. yersinii resembled those of epiphytes or lithophytes. In addition, root anatomy showed several adaptations typical of epiphytes, including the two-layered velamen, thickened exodermal cell walls, well-developed pneumatodes and chlorenchymatous cortex. A well-developed leaf hypodermis as observed in C. yersinii is also unlikely to occur in a terrestrial plant inhabiting wet montane forest. All available evidence thus supports the epiphytic or lithophytic nature of C. yersinii. Eroded roadsides with bare mineral soil seem to accurately mimic epiphytic conditions and offer a suitable secondary habitat to plants otherwise growing on trees or rocks. Other epiphytic species (e.g., C. birmanicum and Thrixspermum annamense) grew there in sympatry. Primary habitats of the new orchid species are most likely trunks of trees; a single epiphytic plant was recorded close to locus classicus in 2014.

Jan Ponert, Pavel Trávníček, Truong Ba Vuong, Romana Rybková and Jan Suda. 2016. A New Species of Cleisostoma (Orchidaceae) from the Hon Ba Nature Reserve in Vietnam: A Multidisciplinary Assessment. PLoS ONE. 11(3): e0150631.   DOI: 10.1371/journal.pone.0150631