Chrysospleniumramosissimum Y.I.Kim & Y.D.Kim (Saxifragaceae), a new species from Korea

Abstract This study describes and illustrates Chrysospleniumramosissimum, a new plant species from Mt. Seonjaryeong, located in the central region of the Korean Peninsula. The species is most similar to C.valdepilosum but is readily distinguishable by the presence of yellowish-green bracteal leaves during flowering, highly branched sterile branches, shiny silvery dots on sterile branch leaves and larger tubercles on the seed coat.


Introduction
Chrysosplenium L. is a distinct genus belonging to the family Saxifragaceae, as it possesses tetramerous flowers and petaloid sepals (Bensel and Palser 1975;Soltis 2007;Soltis et al. 2001). This genus is primarily restricted to the northern hemisphere except for two species in Chile, with species occurring in eastern North America (two species), western North America (four species), Europe (two species) and eastern Asia, where the greatest number of species are present, numbering approximately 50 (Hara 1957;Spongberg 1972). Although estimates of the number of taxa are controversial due to its complex taxonomy, approximately 70 taxa from the genus are recognised worldwide (Maximowicz 1859(Maximowicz , 1872(Maximowicz , 1877(Maximowicz , 1879Hara 1957;Spongberg 1972;Pan 1986;Ye and Zhang 1994;Wakabayashi and Ohba 1995;Wakabayashi and Takahashi 1999;Han et al. 2011;Bhaumik 2014;Kim 2014;Kim and Kim 2015;Liu et al. 2016;Wakabayashi et al. 2018).
Chrysosplenium has been classified into two sections and 17 series (Hara 1957), of which nine species representing two sections and five series are distributed in Korea (Chung and Kim 1988;Kim andKim 2011, 2105;Han et al. 2011Han et al. , 2012. The series Pilosa Maxim. is known to be endemic to northeast Asia and consists of approximately 20 taxa (Franchet and Savatier 1878;Nakai 1914;Kitagawa 1934;Ohwi 1934;Hara 1957;Pan 1986;Wakabayashi and Takahashi 1999;Han et al. 2011;Kim and Kim 2015). The series is characterised by yellow or white erect sepals, opposite leaves and pilose stems (Hara 1957 During a floristic survey of Mt. Seonjaryeong, located in Pyeongchang-gun, Gangwon-do, Korea in August of 2014, we collected a species of Chrysosplenium with a distinct stem feature (i.e. highly branched sterile branches). Additional fieldwork was conducted from April through July 2015 to collect flowering individuals and seeds for specimen and morphological examinations. After consulting relevant literature on Chrysosplenium (Franchet and Savatier 1878;Nakai 1914;Kitagawa 1934;Ohwi 1934;Hara 1957;Pan 1986;Han et al. 2011;Kim and Kim 2015) and examining herbarium specimens at HHU, TI, KB, KH, KWNU, KUS, IUI, KYO and PE, as well as images of type specimens available at the Global Plants website at JSTOR (https://plants.jstor. org), we recognised that the taxon belongs to the series Pilosa. Upon further examination, the plant was distinguished from all known species of the series based on morphological characters. The species is most similar to C. valdepilosum, which has been considered a variety of C. pilosum but recently recognised as a distinct species (Kim andKim 2011, Han et al. 2011). The new species, however, is readily distinguishable by the presence of yellowish-green bracteal leaves during flowering, highly branched sterile branches, shiny silvery dots on sterile branch leaves and larger tubercles on the seed coat. This leads us to the conclusion that it represents an undescribed species. Here, the new species is described and illustrated.

Morphological observations
Photographs of the habit and macro-morphological characters were taken in the field. Morphological observations and measurements of the new species, based on living and dry plant specimens and preserved materials, were carried out. All morphological characters were observed and photographed with a Zeiss Stemi SV 11 Apo stereoscopic microscope and a Zeiss AxioCam MRc 5 microscope camera. Seed coat characters were revealed by a Hitachi S-3400N scanning electronic microscope.
Etymology. The specific epithet of the new species refers to the highly branched sterile branches after fruiting.

Notes
It is noteworthy that C. valdepilosum and C. ramosissimum are sympatric in the type locality. The former species occupies moist soil at the side of a creek, while the latter inhabits damper parts closer to the main stream. The two species exhibit a high degree of morphological similarity upon flowering but can be distinguished by several characters, including the colour of the bracteal leaves at flowering, the vestiture of the leaves of sterile branches and the excrescence of the seeds (Table 1).
It appears that C. ramosissimum and C. valdepilosum have not been recognised as different lineages until recently due to their sympatric distribution and high morphological affinity. Ignoring the importance of the sterile branch development pattern after fruiting may have been the main cause for the delay of the discovery of the new lineage. Further research on the genetic diversity and discovery of additional populations are necessary for the conservation of C. ramosissimum, an endemic species with a very narrow distribution.
C. ramosissimum may also be similar to C. ramosum due to its highly-branching habit. C. ramosum is also distributed in northeast Asia, including Korea, but belongs to the series Oppositifolia and differs in its spreading sepals (vs. erect) and smooth seeds (vs. tuberculate).