Capparis macrantha sp. nov. (Capparaceae, Brassicales), a new shrub species from a deciduous forest of the Nam Kading National Protected Area (central Lao PDR)

1 The Agro-Biodiversity Initiative, National Agriculture and Forest Research Institute, Vientiane, Lao PDR. 2 Department of Agricultural, Food and Forest Sciences, University of Palermo, Palermo, Italy. 3 Biology Department, Faculty of Natural Science, National University of Laos, Vientiane, Lao PDR. 4,5 International Environmental Cooperation Center, National Instrumentation Center for Environmental Management, Seoul National University, Seoul, 08826, Republic of Korea. 6 Forest Ecology and Environmental Research Unit, National Agriculture and Forest Research Institute, Vientiane, Lao PDR.


Introduction
The flowering plant genus Capparis L. (Capparaceae Juss., Brassicales Bromhead) includes about 140 species (POWO 2019) of shrubs, small trees and climbers widespread in the tropical and subtropical areas of the Old World, with outliers in central Asia and the Mediterranean Region, and occurring from sea level up to ca 3600 m a.s.l. over a wide range of habitats, e.g., bushlands, savannahs, dry evergreen, deciduous or rain forests, rocky habitats, coastal vegetations, forest margins, etc. The Indochinese Peninsula is a major centre of speciation of Capparis, but its taxonomic treatment is still critical in Lao PDR where a discordant number of species has been recorded by different authors (Gagnepain 1908;Jacobs 1965;Newman et al. 2007;Inthakoun & Delang 2008;Lee 2016). Field and herbarium research carried out in the last years in this country have provided new data on the variation and distribution of various poorly known taxa (Fici 2016) and led to the description of three new species from the Hin Nam No and Hin Boun National Protected Areas in central Lao PDR (Fici et al. , 2020Souvannakhoummane et al. 2018). Furthermore a number of new species of Capparis were recently described from neighbouring countries, i.e., Vietnam (Thuong et al. 2013(Thuong et al. , 2015, Thailand (Srisanga & Chayamarit 2004) and China (Zhang & Tucker 2008).
Nam Kading, located in the Bolikhamxai Province, is a poorly explored national protected area of central Lao PDR showing a highly diverse vascular flora. Floristic surveys carried out in this area during the last few years provided documentation of several taxa new for the flora of Lao PDR and led to the description of various new species Tagane et al. 2017Tagane et al. , 2018Yang et al. 2018;Souvannakhoummane et al. 2019). During recent field work in the deciduous forest of Nam Kading NPA, a population of Capparis characterized by large, serial flowers, a high number of stamens and a large ovary was observed. Based on herbarium investigations, material collected from this population turned out to belong to a new species of sect. Monostichocalyx Radlk. The new species is here described and illustrated, and data on its distribution, ecology, conservation status and affinities are furnished.

Material and methods
Field investigations were carried out in the Nam Kading National Protected Area from 2017 to 2019. The new species was first observed and collected by one of us (S.L.) in May 2019 in the deciduous forest of this area and the specimens are kept at the National University of Laos (FOF) and Herbier National du Laos (HNL).
The description and illustration are based on herbarium material. The species concept adopted follows the one proposed by Jacobs (1965) in his revision of the genus Capparis from the Indus to the Pacific. The terminology of vegetative and reproductive structures, as well as the main diagnostic characters within the genus, are based on the same treatment (Jacobs 1965

Etymology
The specific epithet is composed of the Greek words ʻmakrósʼ, meaning ʻlargeʼ, and ʻánthosʼ, ʻflowerʼ.

Distribution, habitat and phenology
The new species is so far known from a single location in the Nam Kading National Protected Area in Bolikhamxai Province, at 18°11′44.9″ N, 104°26′25.1″ E (Fig. 3  (1.
Various other species recorded from Lao PDR and included by Jacobs (1965) in the Seriales-Group, as C. acutifolia Sweet, C. echinocarpa Pierre ex Gagnep., C. micracantha DC., C. pyrifolia Lam., C. tenera Dalzell, C. urophylla F.Chun and C. zeylanica L., are readily distinguished by their small to medium sized flowers, with sepals 3-15 mm long, and by the ovary up to ca 3 mm long (Table 1).

Conservation status
Capparis macrantha sp. nov. is known from the type locality only, occurring in a National Protected Area, where about 10 individuals were observed. Based on our observations, the population is not under immediate threat; however, given the very small area of occupancy known, the new species is assessed here as Vulnerable (VU D1) according to IUCN Red List Categories and Criteria (IUCN 2012).

Discussion
The genus Capparis is represented in Lao PDR by about twenty species (Jacobs 1965;Newman et al. 2007;Fici et al. 2018Fici et al. , 2020Souvannakhoummane et al. 2018), all belonging to sect. Monostichocalyx, characterized by leaves well developed and persistent, and sepals all free in bud, with both sepals of a pair equal (Jacobs 1965) (for a key to the species of Capparis L. in Lao PDR see Supplementary file 1).
Other sections of the genus recorded in southern Asia and the Pacific, i.e., sect. Capparis L., sect. Sodada (Forssk.) Endl. and sect. Busbeckea (Endl.) Benth. & Hook.f. (Jacobs 1965;Fici 2017), are not represented in the Indochinese area. Jacobs (1965) recognized within sect. Monostichocalyx some tentative morphological groups, among which the Seriales-Group includes several species with small to medium-sized flowers arranged in supra-axillary rows. However, the same author underlined that, within the whole genus, the species with serial flowers "are the most difficult to interpret. Most of them have advanced characters, some are taxonomically isolated"; based on his statement that "a serial arrangement of flowers does not imply a common origin", Jacobs (1965) treated a few species showing this reproductive feature in other groups, i.e., C. multiflora Hook.f. & Thomson in the Cataphyllosa-Group (including species with flowers small to large, usually arranged on a bracteate, leafless axis or subumbellate, rarely serial), and C. olacifolia and C. radula in the Brevispina-Group (including species with flowers mostly large and solitary, rarely serial, with elongate ovary). Due to its flower characters, C. macrantha sp. nov. could be better placed in the latter group than in the Seriales one; it is to be underlined that the large size of the flowers and the high number of stamens found in the new species are unusual for sect. Monostichocalyx. With regard to southern Asia, flowers of similar size are recorded in a few species, i.e., C. baducca L. from southern India, differing in the smaller leaves, (7-)9-14 × (3.5-)4-5.5(-6.5) cm, and in the solitary, axillary flowers, and C. trisonthiae Srisanga & Chayam., a species described from Doi Phu Kha National Park in northern Thailand (Srisanga & Chayamarit 2004), which differs in the lianous habit and flowers arranged in terminal leafy panicles.
The discovery of this new species confirms the role of the limestone habitats of Lao PDR in the differentiation in south-eastern Asia of the genus Capparis, which includes several taxa endemic to this country, among which are C.  (Souladeth et al. 2017, 20199;Tagane et al. 2018;Yang et al. 2018;Souvannakhoummane et al. 201). Further floristic research in this less investigated area most likely will add new data to the vascular flora of central Lao PDR.