A new myco-heterotrophic genus, Yunorchis, and the molecular phylogenetic relationships of the tribe Calypsoeae (Epidendroideae, Orchidaceae) inferred from plastid and nuclear DNA sequences.

Guo-Qiang Zhang,Li-Jun Chen,Zhong-Jian Liu,Yong-Yu Su,Si-Ren Lan,Ming-He Li

doi:10.1371/journal.pone.0123382

Guo-Qiang Zhang, Li-Jun Chen + Show 4 more

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https://doi.org/10.1371/journal.pone.0123382

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Abstract

We identified a new holomycotrophic orchid that is related to the myco-heterotrophic Calypsoeae. Because chloroplast genes are primarily lacking or are highly divergent, key morphological characters are either reduced or lost from many myco-heterotrophs, and the phylogenetic relationships of weakly supported paraphyletic Calypsoeae within Epidendroideae have been poorly understood in previous molecular systematic studies. Using chloroplast rbcL, psaB, and matK and nuclear Xdh and ITS sequences, we determined the circumscription and systematic positions of the new orchid and the tribe. The results indicate that the epidendroid taxa include most of the clades that are successively sister to the grade of clades representing previously recognized tribes. Calypsoeae comprising four well-supported clades with 12 genera (except for the previous temporarily placed Wullschlaegelia) is supported as a monophyletic and sister clade to Epidendreae (excluding Coeliinae). The new orchid is nested in Calypsoeae and is a sister to Dactylostalix and/or Calypso. This new holomycotrophic orchid presents a subumbel inflorescence that grows underground, and flower with a long pedicel reputing the ground to open and two fragments at the base of the hook, which are obviously morphologically different from those of Calypsoeae. To accommodate this species in the current generic circumscription, a new genus Yunorchis was created.

Highlights

Nonphotosynthetic mycorrhizal plants have long attracted the attention of botanists and mycologists and have been the target of unabated controversy and speculation [1]
Xiang et al [15] sampled a total of 96 genera for the phylogenetic analysis of Epidendroideae based on the combined chloroplast genes, these authors sampled only one supported groups of Calypsoeae, and the results indicated the two genera is sister to Dendrobieae/Malaxideae in a Bayesian inference with a Posterior probabilities (PP) of 0.80 and unsupported in Maximum parsimony analyses
Parsimony analyses resulted in a parsimonious tree of 2150 steps (TL) with a consistency index (CI) = 0.4647 and a retention index (RI) = 0.5843

Summary

Introduction

Nonphotosynthetic mycorrhizal plants have long attracted the attention of botanists and mycologists and have been the target of unabated controversy and speculation [1]. There are more than 400 species (approximately 90 genera) of fully myco-heterotrophic/holomycotrophic and almost 20 000 partially myco-heterotrophic/heteromycotrophic flowering plants [2]. Myco-heterotrophic angiosperms comprise part of the Burmanniaceae, Corsiaceae, Ericaceae, Gentianaceae, Iridaceae, Orchidaceae, Petrosaviaceae, Polygalaceae, Thismiaceae, and Triuridaceae families. Among these families, Orchidaceae occupies a large number of groups [3]. The majority of holomycotrophic flowering plants are restricted to the tropics, but myco-heterotrophic Ericaceae and some Orchidaceae have been observed in temperate forests [2]. We conducted a field study in the tropics of Yunnan, China, and identified a new holomycotrophic orchid that is morphologically related to the Calypsoeae tribe

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