0 Introduction

Hemiboea C. B. Clarke, a medium-sized genus of tribe Didymocarpaeae, subfamily Cyrtandroideae, in the family Gesneriaceae^[1], distributed in China, South Japan and North Vietnam^[2]. So far, 34 species and 6 varieties have been reported for this genus^[3], among them 35 taxa are found in South China, especially in limestone areas of Yunnan, Guizhou and Guangxi Provinces^[4]. Recently, taxonomic treatments of Gesneriaceae has documented totally 7 species of Hemiboea in Vietnam; H. rubibracteata Z.Y. Li & Yan Liu recorded from Na Hang District, Tuyen Quang Province^[5], H. ovalifolia (W. T. Wang) A. Weber & Mich. M ller and H. gracilis Franch. found in Trung Khanh District, Cao Bang Province^[6], H. longisepala Z.Y. Li newly reported from Tam Dao District, Vinh Phuc Province, H. subcapitata C. B. Clarke and H. cavaleriei Lévl. widely seen in northern Vietnam^[7-8], and H. crystallina Y.M.Shui & W.H.Chen from karst region of China and Vietnam^[9]. It is remarkable that the H. polanei Pellegr. (1926), type species of the genus Deinostigma W. T. Wang (1992) widely accepted in taxonomic treatments of Gesneriaceae in the world^[10-11], but was popularly used in publications from Vietnam^[7-8,12-13]. Because H. sinovietnamica W.B. Xu & X. Y. Zhuang described from the collection at Sino - Vietnam boundary in Guangxi Province^[14] was reported with its distribution in Vietnam but not indicated by voucher specimen and specific locality in Vietnam^[4] and we have not seen this species in Vietnam therefore the species is not included in this paper.

During floristic surveys of limestone mountains in Quan Ba District, Ha Giang Province from 2016 to 2018, several collections of a Hemiboea species were collected. This species is characterized by larger spherical involucres, each with 12-20 longitudinal veins, (3)3.5-4.0 cm in diameter and corolla yellow, glabrous, with a ring of hairs adnate to 6-7 mm above the corolla tube base inside (Fig. 1), which present morphological features of Hemiboea malipoensis Y.H. Tan^[15]. After carefully referring publications of Hemiboea known from China^{[1-2,4,15-18]} and Vietnam^{[5-8,12,19-21]}, we surely conclude that this species has not been reported for the Gesneriads of Vietnam so we here describe and illustrate it for the flora of Vietnam. Moreover, its phenology, distribution, habitat and ecology, and a key of Hemiboea in Vietnam are also provided in this paper.

1 Hemiboea malipoensis Y. H. Tan, Phytotaxa 174 (3): 165-172. 2014

Vernacular name: Đại thư malipo (Vietnamese)

Type: (China. Yunnan Province): Malipo County, Xiajinchang, Shanggaotang, limestone forests, 23° 8 ′ 6″N, 104° 51 ′ 16″E, 1 250 m, 4 November 2011, Yun-Hong Tan 6055 (holotype HITBC!, isotypes IBK!).

Description and illustration (Fig. 1): Terrestrial and lithophytic perennial herb. Stems erect, up to 150 cm tall, simple or branched, glabrous, polished, lenticellate and usually covered by dark purple or violet spots, with (8)10-16(20) nodes; internodes cylindrical, (0.5)2-5(7) cm long, (0.6)0.7-0.9(1) cm in diameter. Leaves decussate, 8-16, petiolate; petiole (1.5)2.0- 3.5(6.5) cm long, glabrous with dark purple spots or patches; leaf blade fleshy, thickly papery when dry, adaxially green, abaxially celadon green, from oblanceolate, oval to obovate, (9)12-19(21) × (4.5)5.5-7.5 (9.5) cm, apex acute to shortly acuminate, base narrowly cuneate to oblique, margin entire or with shallowly glandular teeth, glabrous on both sides; lateral veins (5)6-7(8) on each side of midrib, veins slightly sunken adaxially and raised abaxially. Cymes axillary or subterminal, 3-5(8) flowered; peduncle (2.5)3-5 (6.5) cm long, ca. 5 mm in diameter, glabrous, densely verrucose at receptacle; involucre subglobose or broadly longitudinally compressed ovoid, (3.0)3.5- 4.0 cm in diameter, pale green, glabrous, with 12-20 longitudinal veins, apex acute and usually rotten when flowers open; involucel membranous, transparently dull white. Pedicel (4)5-7(8) mm long, 3-4 mm in diameter, glabrous, verrucose. Calyx yellowish white to white, 5-parted from the base, lobes equal, narrowly lanceolate, (16)17-19(20) × 2.8-3.8 mm, glabrous, pellicular, with a midrib prominent abaxially, apex acute, outward. Corolla yellow, glabrous, 3.8-4.5 cm long. Corolla tube 2.8-3.1 cm long, ca. 1.4-1.6(1.7) cm wide at the orifice, 4-5(6) mm wide at the base, inside glabrous, with a ring of hairs adnate to 5-6 mm above the corolla tube base; limb distinctly 2-lipped; adaxial lip 10-14 mm long, cassideous, sparsely adaxial purple-spotted, abaxial extremely short glandular-puberulent, 2 - lobed, lobes semi-round, ca. 4-5 × 10-11 mm, margin undulate or sinuate; abaxial lip 3-lobed almost to base, lobes ovate, 9-11×6-8 mm, margin undulate or sinuate. Stamens 2, anthers fused by entire adaxial surfaces of anthers, adnate to 10-12 mm above the corolla base; filaments linear, glabrous, geniculate at lower the middle, 16-18 mm long; anthers subrotund, glabrous, ca. 1.5-2.0 mm. Staminodes 3, glabrous, adnate to 10-12 mm above the corolla base, lateral two staminodes thick, 10-11 mm long, central staminode gracile, 5-6 mm long. Disc ring-like, yellow, 2-2.5 mm high, margin slightly repand, glabrous. Pistil 2.5-3.0 cm long; ovary linear, 11-13 × 3-3.5 mm, glabrous; style 14- 17 mm long, glabrous, apex curved; stigma capitate, ca. 1.5 mm in diameter. Capsule linear, 19-28 mm long, 4-5 mm in diameter, glabrous, slightly curved.

Phenology: Flowering in October-November, fruiting in November, possibly to December.

Distribution and ecology: Hemiboea malipoensis, only known from Malipo County, southeastern Yunnan, China^[15], is newly recorded in Vietnam (Hà Giang Province, Quản Bạ District; Tùng Vài and Cao Mã Pờ Communes). H. malipoensis is found at humid, shaded places under the storey of evergreen broadleaved forests on limestone mountains and usually accompanied with Boehmeria sp., Loxostigma glabrifolium D. Fang & K. Y. Pan, Impatiens spp., Elatostema sp., Begonia sp., Asplenium prolongatum Hook.

Conservation status: Based on the coordinate of type locality and our sites, and GeoCAT (http://geocat.kew.org/editor), the EOO and AOO of H. malipoensis are 32.348 km² and 16 km² respectively (polygon with red line and dots in Fig. 2). So far, only 4 localities of this species are recorded in the limestone mountains of Yunnan Province (South China) and Ha Giang Province (North Vietnam), but we believe that more H. malipoensis populations will be found in the limestone mountains of Yunnan and Ha Giang Provinces or other Provinces in southern China and northern Vietnam, then the EOO and AOO of this species will increase up and possible to thousands and hundreds square km respectively but the EOO and AOO possibly could not exceed 5 000 km² and 500 km² respectively (the polygon with black lines and blue dots in Fig. 2). Local people usually harvest stem and leaves of H. malipoensis to feed pigs and collect firewood in Cao Ma Po and Tung Vai Communes. These activities somewhat directly and indirectly caused a decline to the quality of H. malipoensis habitats. Moreover, our field surveys showed that H. malipoensis only occurred in limestone mountains of Tung Vai and Cao Ma Po communes which were severely fragmented by valleys with introduced plants of local people and transportation roads. According to the Guidelines for Using the IUCN Red List Categories and Criteria version 13^[22], we access this taxon as Endangered species (EN B2ab(iii)).

Examined specimens: VIETNAM. Ha Giang Province, Quan Ba District, Tung Vai commune, Thang Village, evergreen broad-leaved forest on limestone mountain, under shaded places, around point 23°03 ′ 19″N, 104°52 ′ 52″E, at elevation of 1 200 m a. s. l. Terrestrial and lithophytic perennial herb, flower yellow, locally common, November 22, 2016, Nguyen Sinh Khang et al., NSK 843 (HN!). Ha Giang prov., Quan Ba distr., Tung Vai com., Thung Pang vill., around point 23°04 ′ 39″N 104°56 ′ 07″E, steep rocky slopes near hill top composed with stratified highly eroded limestone at elevation 1 000-1 100 m a.s.l., remnants of primary evergreen broad-leaved very humid forest. Erect terrestrial and lithophytic herb to 1.5 m tall in shady place, flowers light yellow, locally very common, 17 October 2018, L. Averyanov, Nguyen Sinh Khang, T. Maisak & Truong Duc Thieu, VR 886 (LE!, HN!). Ha Giang prov., Quan Ba distr., Cao Ma Po com., Va Thang 1 vill., around point 23°05 ′ 53″N, 104° 51 ′ 26″E, steep alluvial slopes and flattened mountain summits based on limestone at elevation 1 400-1 500 m a.s.l., primary evergreen broad-leaved very humid forest. Erect terrestrial herb to 1 m tall among shady rocks, flowers pale yellow, not common, 22 October 2018, L. Averyanov, Nguyen Sinh Khang, T. Maisak & Truong Duc Thieu, VR 1232 (LE!, HN!).

2 Notes on taxonomy and identification key for Hemiboea in Vietnam

In comparison with H. malipoensis population from Malipo County^[15], our plants sometimes have more nodes and leaves, up to 20 nodes with 16 decussate leaves (vs. up to 16 nodes, and 10 leaves), longer petiole, (1.5)2.0-3.5(6.5) cm long (vs.2-4 cm), bigger leaves, (9)12-19(21) × (4.5)5.5-7.5(9.5) cm, (vs. 10.5-17.5×5.0-8.5 cm), more longitudinal veins of involucres, 12-20 (vs. 6-12). Those characteristics are quantitative and not stable in this species. The distinguished characteristics of H. malipoensis are green, broadly longitudinally compressed ovoid or subglobose involucres, transparently white or pale membranous involucels, calyx 5-lobed from the base, segments equal, glabrous, corolla yellow, without glandular puberulent outside, and having a ring of hairs adnate to 5-6 mm above the corolla tube base, cassideous shape of adaxial lip, anthers fused by entire adaxial surfaces of anthers.

According to Zhang et al.^[15], H. malipoensis was morphologically closed to H. cavaleriei var. pausinervis W.T. Wang & Z.Y. Li and H. magnibracteata Y.G. Wei & H.Q. Wen. After examining the type specimens and descriptions of the two species, we found that H. malipoensis was easily distinguished from the H. cavaleriei var. pausinervis W.T. Wang & Z.Y. Li with type specimens collected in Guangxi, Napo, 17/10/1979, D. Fang et S. P. Liao 22325^[23], deposited in PE (holotype PE00030787!, isotype PE00030788!) by leave apex usually broadly acute (vs. narrowly acute to acuminate), corolla 3.8-5.5 cm long, glabrous outside (vs.3-3.5 cm, glandular puberulent), and from the H. magnibracteata Y.G. Wei & H.Q. Wen described from Guangxi, Huanjiang County, Mulun village, Hongdong, alt. 650 m, 16 Aug. 1994, Fl. Mulung Exped. M 0224^[24] with holotype IBK00191645!, isotype IBK00191646!, PE00154620! by calyx 5-parted from the base (vs. calyx campanulate, 5-lobed from above middle), cymes 6-10 flowered, peduncles 3-3.5 cm long (vs. 3-6 flowered, ca. 1.5 cm long), corolla yellow, glabrous outside (vs. white to yellow, glandular puberulent outside). H. malipoensis also significantly differs from H. cavaleriei Lévl., which has type specimens (holotype E00135154!; isotype E00135153!, E00061241!), collected from Kouy-Tchéou: Pin-Fa, 16 Sept. 1902, Jul. Cavalerie 492^[25] by the former having leave blade glabrous, (5)6 - 7(8) lateral veins on each side of midrib, margin entire or rarely undulate (vs. sparely pubescent, 6-14, crenuate), corolla glabrous (vs. glandular puberulent outside), and anther completely coherent (vs. apically coherent).

Molecular data show H. malipoensis belongs to a clade including H. longzhouensis, H. longganensis, and H. bicornuta^[15] or related to H. rubibracteata^[3], however the H. malipoensis obviously differs from H. longzhouensis W. T. Wang ex Z. Y. Li^[23] by leave glabrous (vs. adaxially pubescent), corolla yellow (vs. white), glabrous inside (vs. sparsely glandular puberulent), from H. longgangensis Z. Y. Li^[23] by leave oblanceolate, oval to obovate, glabrous, 5-8 lateral veins on each side of midrib (vs. narrowly elliptic-lanceolate, abaxially sparsely pubescent, 8-12 lateral veins on each side), cymes 3-5(8) flowered, glabrous (vs. 2-3 flowered, glandular pubescent), involucres glabrous (vs. glandular pubescent), calyx and margin glabrous abaxially (vs. glandular puberulent), corolla glabrous outside (vs. glandular puberulent), pistil glabrous (vs. sparsely glandular puberulent), from H. bicornuta (Hayata) Ohwi by leave oblanceolate, oval to obovate (vs.elliptic to narrowly lanceolate), abaxial veins glabrous (vs.pubescent), 5-8 lateral veins on each side of midrib (vs. 6-10), corolla yellow (vs. white), anthers ca. 1.5-2.0 mm (vs.3 mm), pistil 2.5-3.0 cm long (vs. 1.5-2 cm), disc ring-like 2-2.5 mm high (vs.1 mm)^[2], and from the H. rubribracteata Z. Y. Li & Yan Liu^[26] by leave margin entire or with shallowly glandular teeth (vs. serrate to crenate), 5-8 lateral veins on each side of midrib (vs. 6-15), involucres green (vs. red), calyx white (vs. purple), corolla yellow (vs. white), glabrous inside (vs. glandular puberulent), filaments 16-18 mm long (vs. 10-15 mm), anthers completely coherent (vs. apically coherent), capsule 19-28 mm long (vs. 14-18 mm).

3 Identification key to Hemiboea species known from Vietnam

1a. Stem covered densely white villous hairs…………………………………… H. ovalifolia

1b. Stem glabrous …………………………………………………………………………2

  2a. Involucres outside purplish white to red……………………3

    3a. Involucres purplish white, lateral veins 4-6 on each side of midrib, cymes 1-3 flowered………………H. gracilis

    3b. Involucres red, lateral veins 6-15 on each side of midrib, cymes 6-9 flowered…………………………H. rubribracteata

  2b. Involucres green………………………………4

    4a. Corolla outside glabrous ………….5

      5a. Lateral veins 5-8 on each side of midrib, corolla yellow …………………………………………… H. malipoensis

      5b. Lateral veins 10-12 on each side of midrib, corolla white…………………………………………… H. longisepala

    4b. Corolla outside not glabrous (glandular puberulent or pubescent)………………………………………6

      6a. Corolla outside pubescent, inside glabrous ………………………………………………………… H. crystallina

      6b. Corolla outside glandular puberulent, inside with a ring hair adnate to corolla tube base……………7

      7a. Leave base decurrent, calyx segments 6-12 × 3-4.5 mm, pistil 3-4 cm long………… H. subcapitata

      7b. Leave base not decurent, calyx segments 5-7 × 0.2-0.4 mm, pistil 1.7-2.5 cm long… H. cavaleriei