Genus Metagentiana T. N. Ho & S. W. Liu (Gentianaceae Juss.) – a new record for flora of Vietnam

Ho et al. proposed to exclude Stenogyne section from the genus Gentiana and classifying it as a distinct genus (Metagentiana). Fourteen species of this genus have been recorded and distributed in China, Myanmar and Thailand. This is the first time there has been a confirmed genus Metagentiana distributed in Vietnam. This genus has two species: Metagentiana rhodantha and Metagentiana primuliflora, which are proposed in Vietnam. Particularly, Metagentiana rhodantha, which had only been known from China, was reported in Vietnam. A detailed description along with their distribution, habitat, ecology, illustrations, and photos has been provided to aid species identification. The key to identify all taxa of the genus has been


Introduction
Stenogyne is one of Gentiana's 16 sections, belonging to the gentian family (Gentianaceae Juss.) [1]. It was established by Franchet [2] and was revised by Kusnezov [3]. It is the most disputable and poorly known of Gentiana's 16 sections.
Genus Metagentiana was established by Ho et al [4] on the basis of removing the Stenogyne section from the genus Gentiana based on data on gross morphology, floral anatomy, chromosome number, palynology, embryology, and molecular data. Before Ho Ting Nong, many botanists considered it as a section of the Gentiana genus [5][6][7]. However, contrary to the point of view of many authors at that time, Smith [8] and Löve [9] based on observations of gross morphology, realized the difference between the Stenogyne section and the sections another in the genus Gentiana and its close relationship with the genera Tripterospermum and Crawfurdia. Löve and Löve (1976) proposed to transfer this section to the genus Tripterospermum, which is intended to be a new subgenus of this genus [10] also noticed this difference, but in his classification, the author classified this section as a subgenus of the genus Gentiana. Subsequent authors' karyological studies continued to support evidence that this section differs from the other sections in the genus Gentiana [11][12][13][14]. Authors [12][13] in their initial studies, published chromosome numbers for six species belong to this section; at the same time, based on their differences in the number of haploid chromosomes. They suggested to separate the location of this section within the genus Gentiana. Their subsequent research results on ITS sequencing of the DNA ribosome continued to confirm the difference of the Stenogyne section compared to other sections in the Gentiana genus [14]. Thereafter, species of this section continue to be studied by many authors in a relatively comprehensive way [15][16][17][18][19][20][21][22][23][24][25][26]. Based on the summary of research data of previous authors and based on their own research, suggested removing Stenogyne section from the genus Gentiana and classifying it as a distinct genus (Metagentiana) [4]. They affirmed that this new genus was more related to Tripterospermum and Crawfurdia than to Gentiana, though it was more primitive than the first two genera; together with Tripterospermum and Crawfurdia the new genus formed a monophyletic group, which was the sister group to the genus Gentiana [4]. Fourteen species (Chinathirteen species; Myanmarone species and Thailandone endemic species) of the genus Metagentiana have been proposed. The species of this genus are mainly distributed in high mountains, grassland, and coniferous forests.
In Vietnam, Loureiro [27] was the first botanist to study on Gentiana genus; two species of this genus have been recorded by the author to be distributed in Vietnam. The "Flore du Cambodge, du Laos et du Vietnam" [28] is considered the most complete classification work of this genus in Vietnam; nine species of the genus distributed in Vietnam were authored detailed description, including Gentiana primuliflora species (belonging to Stenogyne section) which was first recognized by the author to be distributed in Vietnam, it was previously endemic to China. During the course of revisionary on the Gentianaceae in Vietnam, interest arose in the specimens, which were housed in the herbarium of Institute of Ecology and Biological Resource, Hanoi (HN). After thorough morphological study with the help of the relevant literature [1,4,[27][28][29][30], it was identified as Metagentiana rhodantha (Franch.) T. N. Ho & S. W. Liu, a new distributional record for Vietnam. This taxon was so far known only from China [4] and had never been recorded in Vietnam.
Earlier, Hul Sovanmoly [28] recorded species Gentiana primuliflora Franch.in Vietnam, distributed in Da Lat city (Lam Dong province). The specimen is currently stored in herbarium of Hanoi National University (HNU) and Muséum National d'Histoire Naturalle, Paris (P). We have been revised this species name to Metagentiana primuliflora (Franch.) T. N. Ho & S. W. Liu… This is the first time there have been a confirmed genus Metagentiana distributed in Vietnam. This genus has two species: Metagentiana rhodantha and Metagentiana primuliflora, which are proposed in Vietnam. In this article, we describe the characteristic of genus Metagentiana and two specises of this genus in Vietnam along with brief information about their distribution, habitat and ecology; illustrations and photos have been provided to aid species identification. The key to identify all taxa of the genus has been constructed.

Material and methods
The study area covers the entire territory of Vietnam. The collected specimens were processed and preserved in the herbarium of Institute of Ecology and Biological Resource, Hanoi (HN). In addition, we also researched dry specimens that were kept in the herbarium of Hanoi National University (HNU); the herbarium of Institute of Herbs annuals or perennials. Stems erect; branches spreading, 4-angled. Leaves opposite, sessile to subsessile; leaves blade usually elliptic, ovate to cordate, margin serrulate, base rounded to cordate, apex acute; veins 3 or 5. Flowers terminal on branches, solitary, 5-merous, sessile, subtended by a pair of leaf-like bracts. Calyx tubular; tube membranous, 5angled; lobes 5, midvein prominent outside and decurrent into angles of calyx tube. Corolla tubular to funnelform or salverform; tube usually much longer than lobes, lobes triangular or ovate; plicae between lobes, asymmetrical, very oblique, margin long fringed or erose. Stamens 5, unequal; filaments inserted on corolla tube; anthers narrowly ellipsoid. Ovary superior, 1-locular, ellipsoid; style filiform, about as long as ovary; stigma 2-lobes, linear. Capsule included in persistent corolla, ellipsoid, wingless, many seeded. Seeds brown, triquetrous, ellipsoid, ovoid to subglobose, winged or wingless.
In the world, fourteen species of the genus Metagentiana have been recorded, distributed in China, Myanmar, and Thailand. In Vietnam, two species have been recorded of this genus, distributed in north and central Vietnam.

Conclusion
In this study, we agreed with   [4] when proceeding to separate Stenogyne section from the genus Gentiana and classify it as a separate genus (Metagentiana). During the research, we have classified nine species of the genus Gentiana (Fig. 1) and two species of the genus Metagentiana that are distributed in Vietnam. This is the first time there has been a confirmed genus Metagentiana distributed in Vietnam. This genus has two species: Metagentiana rhodantha and Metagentiana primuliflora, which are proposed in Vietnam. Particularly, Metagentiana rhodantha, which had only been known from China, was reported in Vietnam. A detailed description along with their distribution, habitat, ecology, illustrations, and photos has been provided to aid species identification. The key to identify all taxa of the genus has been constructed.

Authors' contributions
This study was performed in collaboration between all authors. The two first authors, Khuat Van Quyet and Nguyen Thanh Hai, were the main investigators of the study. Other authors participated in the collection of materials, the preparation of experiments, and data collection. Kalashnikova E.A. designed the study, wrote the manuscript, and is the corresponding author of this research.