Hemiboea chanii (Gesneriaceae), a new species from limestone areas of northern Vietnam

Hemiboea chanii, a new species of Gesneriaceae from Ha Giang Province, northern Vietnam, is here described and illustrated. It has many branched stems, diamond-shaped involucre with two cirrose opposite apices, a pink corolla, red spotted inside, and a flowering time in January-February. Among congeners with an externally hairy corolla, this new species is morphologically close to H. crystallina and H. sinovietnamica. Diagnostic discriminative characters in all mentioned species are discussed. The conservation status of this species is considered to be “Critically endangered” (CR) according to the IUCN Red List Categories and Criteria.


Introduction
Prior to 2011, Hemiboea Clarke (1798) (Gesneriaceae) contained about 23 species and 5 varieties, distributed mainly from northern Vietnam to southern and eastern China to southern Japan (Weber 2004;Li and Wang 2004). In 2011 the formerly recognized genus, Metabriggsia W.T. Wang (1983), with two species, Metabriggsia ovalifolia W.T.Wang and Metabriggsia purpureotincta W.T.Wang, was revised and merged with Hemiboea (Weber et al. 2011). During last two decades, 14 new taxa were found and described in China and Vietnam: 13 new species and one new variety from Guangxi, Guizhou and Yunnan provinces of southern and southwestern China ) and one from Thanh Hoa Province of northern Vietnam (Nguyen et al. 2019a). In addition, based on extensive morphological, phenological, and molecular studies, H. subcapitata var. pterocaulis Z.Y.Li (Li 2004) was accepted as a distinct species H. pterocaulis (Z.Y.Li) J.Huang, X.G.Xiang & Q.Zhang in Huang et al. (2017). Similarly, Li et al. (2019). In total, before our study, the genus Hemiboea comprises at least 39 species and 5 varieties.
During the botanical fieldwork in limestone areas of Ha Giang Province in northern Vietnam in spring 2021, we collected an unusual species of Hemiboea. The genus characteristics are calyx 5-parted to the base, stamens 2, staminodes 3, stigma 1 (undivided), and capsule oblique in relation to pedicel, narrowly lanceolate, somewhat curved, dehiscing adaxially; valves 2, straight, not twisted. After consulting relevant literature of Hemiboea (Wang et al. 1998;Pham 2000;Li and Wang 2004;Wei et al. 2010;Do et al. 2016;Luu et al. 2018;Wei 2018;Nguyen et al. 2019b) including recently published papers for new taxa of Gesneriaceae from Vietnam (e.g. Michaelmoelleria F.Wen, Y.G. Wei & T.V.Do in Wen et al. 2020) as well as the examining of herbarium specimens, we identified our plants as a new species, well segregated from all known species of Hemiboea by its morphological characters, namely a diamondshaped involucre with a cirrose apex; a 1-veined calyx with flat, not revolute margin; a pink corolla with red spots, and a slightly swollen stigma. This new species is described and illustrated here as H. chanii C.H.Nguyen & Aver.

Material and methods
All collected and studied specimens of the newly discovered species are presently stored in the Herbaria of China, Russia, and Vietnam (IBK, IBSC, KUN, LE, PE, VNF). The photographs used for the species illustration were taken in the species natural habitats. Morphological observations and measurements were made on living plants, dry specimens, and materials preserved in alcohol. Morphological characters are described using the terminology proposed by Wang et al. (1998). H.Chen in the shape of leaf blade, leaf margin and the externally pubescent corolla, but differs in having non-inflated nodes, diamond-shaped not winged involucre, flat calyx margin, corolla red-spotted inside with a ring of hairs, and stigma slightly swollen. It also morphologically resembles H. sinovietnamica W.B.Xu & X.Y.Zhuang but differs in having 4-8 branches on main stem, repand-crenate leaf margin, involucre diamond-shaped with a cirrose apex, and pink corolla and a slightly swollen stigma (Table 1).
Distribution and habitat. The new species is only known from Minh Tan Village, Ha Giang Province, growing in cracks of limestone rocks in moist shady places or occasionally in the upper part of slopes, and on rocky hilltops in primary evergreen broad-leaved forests on karstic limestone at elevations 500-700 m a.s.l. Some of main herbaceous species accompanying the new species have been recorded as Aglaonema modestum Schott ex Engl., Amorphophallus tonkinensis Engl. & Gehrm., Begonia spp., Impatiens bonii Hook.f., Laportea interrupta (L.) Chew, Primulina balansae (Drake) Mich.Möller & A.Weber, and Rhaphidophora decursiva (Roxb.) Schott Phenology. Flowering from January to February, and fruiting from February to April.
Etymology. Hemiboea chanii is named in honor of the lecturer, Mr. Le Mong Chan, for his outstanding contributions to the conservation of the flora of Vietnam.
Proposed IUCN conservation status. At present, only one known population with less than 100 mature individuals is confirmed in the field assessment. Its estimated area of occupancy is less than 5 km 2 . The population and habitat are greatly susceptible to various human activities and damage, particularly forest logging, agriculture, and grazing. There is a high risk of habitat degradation in the future because it is located close to the local village. Following the IUCN Red List Categories and Criteria (IUCN 2017), the new species may be assessed tentatively as Critically Endangered [B2ab (ii, iii), CR].
Note. Hemiboea chanii is morphologically similar to H. crystallina and H. sinovietnamica in its ecology. It has only been found in a limestone area and grows in the evergreen broad-leaved forest. The new species can be easily distinguished from H. crystallina in having a subterete stem up to 90 cm tall (vs. stem terete up to 40 cm tall), non inflated nodes (vs. nodes inflated), 1-veined calyx with flat, not revolute margin (vs. calyx 3-veined with revolute margin), corolla red spotted inside with a ring of hairs (vs. corolla inside purplish-red spotted with pale yellowish lines and absence of hair ring), and stigma slightly swollen (vs. stigma not swollen). The new species differs from H. sinovietnamica in having a subterete, 4-8 branched stem up to 90 cm tall (vs. stem subtetragonal, simple, up to 45 cm tall), repand-crenate leaf margin (vs. entire leaf margin), involucre diamond-shaped with a cirrose apex (vs. involucre triangular with acute apex), corolla pink (vs. corolla yellowish), stigma slightly swollen (vs. stigma distinctly capitate), and a flowering period lasting in January-February (vs. flowering period lasting during August-October). The comparison of the key morphological characters of H. chanii, H. crystallina, and H. sinovietnamica is presented in Table 1.