Langbiangia, a new genus of Gesneriaceae endemic to Langbiang Plateau, southern Vietnam and a taxonomic endeavor to achieve key targets of the post-2020 global biodiversity framework

Abstract

Situated in the southern end of the Annamite Mountain Range, Langbiang Plateau is a major biodiversity hotspot of southern Vietnam known for high species diversity and endemicity. To achieve effective conservation, parts of the plateau were designated as the Langbiang Biosphere Reserve, an UNESCO World Network aiming to improve relationships between inhabitants and their environments. Amongst the rich endemic flora of the plateau are three gesneriads ascribed to Primulina, a calciphilous genus with high species diversity in the vast limestone karsts stretching from southern China to northern Vietnam. However, a recent phylogenetic study questioned the generic placement of the Langbiang Primulina, corroborating with observations on the geographical distribution, habitat preference, and phyllotaxy of the three species. Based on phylogenetic analyses of nuclear ITS and plastid trnL-F DNA sequences of a comprehensive sampling covering nearly all genera of the Old World Gesneriaceae, we demonstrate that the three Langbiang Primulina species form a fully supported clade distantly related to other Primulina. As this clade is biogeographically, ecologically, morphologically, and phylogenetically distinct worthy of generic recognition, we propose to name it Langbiangia gen. nov. to highlight the rich and unique biodiversity of the Langbiang Plateau. By means of this taxonomic endeavor, we are hoping to raise the conservation awareness of this biodiversity heritage of southern Vietnam and promote the importance of Langbiang Biosphere Reserve that is crucial for achieving action-oriented global targets of the post-2020 global biodiversity framework (GBF) of the UN Convention on Biological Diversity (CBD)-effective conservation and management of at least 30% of biodiverse terrestrial, inland water, and costal and marine areas by 2030-that has been agreed at the COP15 in Montréal in December 2022.

Fig 1. Broad-leaved evergreen forest and expanding coffee plantation in Langbiang Plateau.

As in much of the tropical countries, the biodiverse montane forests of the Langbiang Plateau are being cleared for agriculture such as coffee plantation, threatening the native flora and fauna and the ecosystem functions (photo: C.-W. Chen).

Fig 2. Distribution of Langbiangia and Primulina.

The map was generated using QGIS 3.24.1 [60]. The basemap of karst aquifers was downloaded from WHYMAP [61], which can be freely used and copied for educational and other non-commercial purposes. The distributions were mapped based on occurrence records retrieved from Global Biodiversity Facility [62]. The distribution of Langbiangia poilanei was plotted based on information taken from the holotype. This work is licensed under a CC BY 4.0 license.

Fig 3. Langbiangia poilanei.

(A) Habit. (B) Corolla, longitudinal dissection with stamens. (C) Disc, ovary and style. Photos by Hong Truong Luu and Minh Tri Dang.

Fig 4. Phyllotaxy of Langbiangia and Primulina.

(A) Langbiangia annamensis, photo by Maxim S. Nuraliev / CC BY-NC 4.0 (https://www.inaturalist.org/observations/38536524) (B) The acaulescent stem of Langbiangia scutellifolia. (C) Primulina minutimaculata. (D) Primulina dryas. (E) Primulina lungzhouensis. (F) Primulina minor. B–E by C.-L. Hsieh, and F by K.-F. Chung.

Fig 5. Simplified Bayesian inference tree of Didymocarpoideae based on combined trnL-F and ITS sequences.

Numbers at the node indicate Bayesian posterior probability (≥ 0.5), with ML bootstrap value (≥ 50%) shown after slash (/). All genera except for Primulina, Deinostigma and Langbiangia gen. nov. are collapsed into triangles, with gray triangles denoting genera/clades that are fully supported in both Bayesian and ML analyses. The infrafamilial classification of Weber et al. 2013 [77] and Weber et al. 2020 [63] is followed. This tree is simplified from the S3 Fig. ML bootstrap values are retrieved from S5 Fig.