Paraholcoglossum and Tsiorchis, two new orchid genera established by molecular and morphological analyses of the Holcoglossum alliance

Abstract

Background: Holcoglossum is a small orchid genus of 12 species ranging from SW China to Thailand and NE India. Although molecular and morphological analyses have been performed to establish the phylogenetic relationships within this genus, the interspecific relations and its relations with allied genera, such as Rhynchostylis, Aerides and Vanda, remain unclear.

Methodology/principal findings: In addition to morphological analysis, maximum parsimony, maximum likelihood, and Bayesian inference analyses were performed based on fragments of the nuclear ITS and chloroplast trnL-F and matK genes of 31 taxa (15 Holcoglossum, 14 Aeridinae, 2 outgroups) representing all major clades of the Holcoglossum alliance. The results suggest that Holcoglossum is triphyletic, comprising three clades: the Holcoglossum clade, its sister clade, and a distant clade more closely related to Rhynchostylis, Aerides, and Vanda than to the Holcoglossum clade. The Holcoglossum clade is further divided into three subclades; the genetic distances between these three subclades also support this delimitation. The molecular conclusion is consistent with their distinct morphological characters.

Conclusions: We propose that the latter two clades comprise two new genera, Paraholcoglossum and Tsiorchis, and Holcoglossum clade divides into three sections. In addition, a new section, Holcoglossum sect. Nujiangensia, and a new species, Holcoglossum linearifolium, are proposed. Some new combinations are made, and a new scheme is provided for the classification of all species of Holcoglossum, Paraholcoglossum, and Tsiorchis.

Figure 1. Bayesian consensus trees based on the last 30,001 maximum likelihood trees for the combined datasets of ITS, trnL-F, and matK.

The Bayesian posterior probability (×100) is given below the branches.

Figure 2. One phylogenetic tree of Bayesian inference consensus trees based on the last 30,001 maximum likelihood trees for the combined datasets of ITS, trnL-F, matK, and morphological characters matrix.

The Bayesian posterior probability (×100) is given near the node.

Figure 3. Key to the genera, sections, and species of Paraholcoglossum, Tsiorchis, and Holcoglossum.

Figure 4. Holcoglossum linearifolium Z. J. Liu, S. C. Chen & L. J. Chen:

1. Flowering plant; 2. Flower, front view; 3. Flower, side view; 4. Lip and column, longitudinal section; 5. Dorsal sepal, petal and lateral sepal; 6. Pollinarium, front view and back view (Drawn by X. Y. Ma from type Z. J. Liu 4865).