苦苣苔科凹柱苣苔屬在越南的發現及水晶凹柱苣苔的補充描述

陸昭岑 NGUYEN Khang Sinh PHAN Ke Loc4 TRAN Thi Phuong Anh 許為斌

摘 要：? ?中越邊境喀斯特地區有著異乎尋常的植物多樣性，已經成為全球生物多樣性研究和保護的熱點區域，近年來在該區發現了多個苦苣苔科植物的新種或新屬。凹柱苣苔屬是2010年才被建立的新屬，該屬的花與葉相比，花較大，葉相對較小，葉片邊緣稍外卷，花序僅單花，柱頭盤狀或凹坑狀，蒴果長橢球形而有別于苦苣苔科的其他屬。凹柱苣苔屬為喀斯特專性植物，目前僅包括分布于黔西南的凹柱苣苔和分布于滇東南的水晶凹柱苣苔兩個物種。作者在開展中越邊境喀斯特地區植物多樣性調查時，在越南北部的河江省發現了水晶凹柱苣苔，基于該新發現居群的植物標本，對其進行了補充描述，確認其花期為11月—12月，并對該物種瀕危狀況進行了重新評估，同時提供了野外生態照片以資辨認。目前，越南已記錄苦苣苔科植物32屬150余種，凹柱苣苔屬在越南北部的發現，不僅豐富了該國苦苣苔科植物的多樣性，再一次充分證明了中越邊境喀斯特地區是一個完整的植物區系地理單元，而且為稀有的水晶凹柱苣苔提供了更加豐富的野外本底資料，對其將來的深入研究和保護具有重要的生物地理學和保護生物學意義。

關鍵詞：? 越南植物區系， 石灰巖植物區系， 中越邊境喀斯特地貌

1 Introduction

The genus Litostigma Y. G. Wei， F. Wen & M. MOller was described with two species from limestone areas of southern China， Litostigma coriaceifolium Y. G. Wei， F. Wen & M. MOller （Typus generis） was recorded from southwestern Guizhou， and Litostigma crystallinum Y. M. Shui & W. H. Chen was found from southeastern Yunnan， China （Wei et al.， 2010）. Litostigma crystallinum only occurred at limestone caves in Malipo County， Yunnan， southwestern China， near the Sino-Vietnamese boundary when it was published， so it maybe also distributed in northern Vietnam due to its similar habitat and proximity to the type locality （Wei et al.， 2010）. Until now， two collections of Litostigma crytallinum had been collected in Ha Giang Province， northern Vietnam， but they are not recorded for the Gesneriaceae of Vietnam in any relevant literatures from Vietnam （Pham， 2000; Vu， 2005， 2017; Luu et al. 2018）. According to the original literature and specimens from northern Vietnam， the supplementary description， ecology， and colour photos of Litostigma crystallinum are provided here.

2 Taxonomic treatment

Litostigma? Y. G. Wei， F. Wen & M. MOller in Edinb. J. Bot.， 67 （1）： 178. 2010. Type： Litostigma coriaceifolium Y. G. Wei， F. Wen & M. MOller

Perennial， stemless， rhizomatous herbs. Leaves basal， distinctly petiolate. Cymes 1-flowered， 1- bracteate. Sepals 5. Corolla zygomorphic， infundibuliform ， adaxial lip 2-parted， abaxial lip 3-parted， all lobes? divided nearly to the base， orbicular-ovate. Stamens 2， staminodes 3. Disc annular， ovary ovoid-ellipsoid， 1-loculed; placentae 2， parietal， intrusive， bifid. Stigma crateriform or disciform. Fruit narrowly ovoid， glabrous， dehiscing into 4 valves. Seeds reticulate， with raised testa cell walls. Only two species in the genus Litostigma at present， L. coriaceifolium is endemic to southwestern Guizhou， China， and L. crystallinum is endemic to the limestone areas of boundary between northern Vietnam and southwestern China.

Litostigma crystallinum? Y. M. Shui & W. H. Chen in Edinb. J. Bot.， 67 （1）： 181. 2010. （Fig. 1）

Perennial herb， stemless. Rhizome subterete， 3-5 mm long， 2-3 mm in diameter. Leaves 5-14， basal; leaf blade thickly papery， elliptic， 4.5-8 cm long， 3-5 cm wide， apex acute， obtuse to rounded， base broadly cuneiform， margin entire， slightly revolute， glabrous， green above， greyish green beneath; lateral veins 5-6 on each side of midrib， flat adaxially and prominent abaxially; petiole 4-15 cm long， glabrous. Cymes 1-2， 1-flowered; peduncle 3-10 cm long， pubescent; 2-bracteate， small， lanceolate， ca. 3 × 0.8 mm; pedicel 2.5-3 cm long， pubescent. Sepals 5， lanceolate， ca. 7 × 2 mm， pubescent outside， glabrous inside. Corolla purple， infundibuliform， 1.5-2.1 cm long， slightly pubescent outside， glabrous inside; corolla tube 0.7-1.2 cm long with short proximal undilated part， 2 yellow spots inside the tube under the anthers; adaxial lobes 2， rather oblong， ca. 7 × 6 mm， abaxial lobes 3， oblong or obovate， 7-9 × 6-7 mm. Stamens 2 in anterior position， adnate to ca. 3 mm above base of corolla tube; filaments linear， slightly erect， ca. 4 mm long; anthers elliptic， ca. 2 mm long， pilosous， coherent adaxially. Staminodes 2， 1-2.5 mm long， glabrous， adnate to 2-3 mm above corolla base. Disc annular. Pistil 1.2-1.5 cm long; ovary ovoidellipsoid， ca. 1.5 mm long， ca. 1 mm in diameter， 1-loculed with 2 parietal and intrusive placentae; style 9.5-13 mm long， pubescent. Stigma disciform， ca. 0.5 mm in diameter. Fruit 4-5 mm long， narrowly ovoid， glabrous， dehiscing into 4 valves. Seeds ovoid， obliquely reticulate with raised testa cell walls， 0.3 × 0.1 mm.

Distribution and habitat：? So far， only two localities have been recorded for the Litostigma crystallinum， one is in Tianbao Town， Malipo County， Yunnan Province， China， and the other closed to Yunnan Province is in Du Gia Commune， Yen Minh District， Ha Giang Province， Vietnam. L. crystallinum grows on the moist rock surface of the entrance of limestone caves at elevation of ca. 850 m a.s.l. in China and on the humid open cliffs of travertine caves at elevation of 500-850 m a.s.l. in Vietnam.

Phenology：? Flowering from November to December.

Conservation assessment：? According to Wei et al. （2010）， Litostigma crystallinum， was assessed as Critically Endangered （CR）? [B1ab（v）+C2a（i）+D] based on the single population found in the type locality with steadily declined mature individuals recorded from 2002 to 2008. However， with the newly discovered population having many mature plants in Vietnam， about 40 km away from the northwestern type locality， and the extent of occurrence of this species more than 100 km2 but it will be less than 5 000 km2. Thus， following the IUCN （2019） red list categories and criteria， we propose the conservation status of L. cystallinum as Endangered （EN）? [B1ab （iii，v）]. At the same time， we believe that more populations of L. crystallinum will be found out at cave mouths in many limestone areas between southeastern Yunnan， China and Ha Giang， Vietnam if field investigations are extensively conducted there.

Specimens examined：? —VIETNAM.? Ha Giang ： Yen Minh， Du Gia， Giang Chu， 105°09′47″ E， 22°56′54″ N， alt. 540 m， 15 November 2004， Ching-I Peng et al. 20212 （HAST 111912！）; Yen Minh， Du Gia， 105°10′24″ E， 22°56′51″ N， alt. 500-850 m， 28 November 2004， S.K. Wu et al. WP738 （MO 04825175！）.

3 Disccusion

Hitherto，the number of species and genera of Gesneriaceae in Vietnam have not been adequately inventoried， while Vu （2017） recorded 147 species of 31 genera of Gesneriaceae for the Flora of Vietnam， Luu et al. （2018） only recognized 130 species of 28 genera in Vietnam. In recent years， some new taxa or records of Gesneriaceae have been reported from the boundary between northern Vietnam and southern China （Do & Vu， 2011; Vu et al.， 2011; Truong et al.， 2016; Chen et al.， 2018; Nguyen & Wen， 2018; Yang et al.， 2018; Nguyen et al.， 2019; Wen et al.， 2020）， which sufficiently demonstrates a closely floristic relationship of Gesneriaceae between northern Vietnam and southern China， especially the Sino-Vietnamese limestone karsts. The discovery of Litostigma crystallinum from northern Vietnam once again proves the above statement.

Acknowledgements? We are grateful to the curators and staffs of HAST， HN， IBK， KUN， MO， PE and SING offering facilities to check Gesneriad specimens and special to Dr. KF Chung （HAST） and Dr. DJ Middleton （SING） for their enthusiastic help.

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（ 責任編輯 何永艷 ）