Astilbe uljinensis (Saxifragaceae), a new species from South Korea

Abstract A new species Astilbe uljinensis B.U.Oh & H.J.Choi is described from Gangwon-do and Kyeongsangbuk-do in South Korea based on its morphological characteristics and distributional pattern. A. uljinensis is easily distinguished not only from three other Astilbe species in South Korea, but all other species in the genus by possessing a green young rachis, dense long whitish glandular hairs on the young rachis, dense long brownish glandular hairs on the mature inflorescence, and a slightly undulated margin of leaf epidermal cells. Specific comparisons of morphological features such as the type of the trichome, the shape of the leaf epidermis cell, and the color of the young rachis that differentiate A. uljinensis from Astilbe chinensis, another South Korean Astilbe species, are provided.


Introduction
Astilbe Buchanan-Hamilton. & D. Don (Saxifragaceae, Saxifragales) is composed of approximately 18 species which are distributed in eastern and southern Asia, and eastern North America (Pan 1985). Here, eastern and southern Asian regions include Russia, India, Bhutan, Nepal, Thailand, Indonesia, Philippines, South Korea, China, and Japan. The distributional pattern of the genus exhibits a clear geographical disjunction between eastern Asia and eastern North America (Li 1952;Pan 1995;Kim et al. 2009;Zhu et al. 2013).
In this study, we report a previously undescribed species whose morphology is clearly distinct from all other species of Astilbe. This undescribed species is restricted to Kyeongsangbuk-do (Uljin-gun) and Gangwon-do (Gangneung-si, Pyeongchanggun, Samcheok-si), the central regions of South Korea, particularly on the eastern and southern sides of the Baekdudaegan mountain ranges near the eastern coast. Based on morphological and distributional characteristics, this species is identified and described as a novel species from South Korea.

Materials and methods
For species description, the type materials in the herbarium of Chungbuk National University (CBU), which were collected by the authors between May 2013 and September 2015, were examined. The vouchers in the herbarium of Korean National Arboretum (KH) and the herbarium of Kangwon National University (KWNU) were also investigated. In addition, the specimens were investigated extensively in the wild, and some of the collected plants of the novel species were planted in the cultivation facility of Chungbuk National University for the study of their morphology. Between 10 and 30 individuals were used in the quantitative morphological feature measurements.
A comparison with a related taxon was made against Astilbe chinensis, one of the South Korean Astilbe species that is morphologically most similar to the newly described species. A. chinensis is distributed in the East Asian countries of South Korea, China, Russia and Japan (Pan and Ohba 2001;Han and Oh 2019). In some previous studies, this species was incorrectly considered as a synonym of Astilbe rubra, which is distributed in China and India (Lee 1996a;Ohba 2001;Kim 2007;Kim et al. 2009). The vouchers of A. chinensis in the herbarium CBU and the living plants in the cultivation facility at Chungbuk National University were examined for the comparison. A previous study on South Korean Astilbe species (Han and Oh 2019) was also referred to for the information on A. chinensis.
The morphological observations throughout this study were performed using Zoom 2000 (Leica, Germany), a stereoscopic microscope, ECLIPSE E600 (Nikon, Ja-pan), a light microscope, and JSM-700F (Jeol, Japan), a scanning electron microscope. The brownish glandular hairs on the inflorescence and the whitish glandular hairs on the young shoots were observed using the stereoscopic microscope, and the epidermal cells and the stomatal apparatus were observed using the light microscope and the scanning electron microscope. Diagnosis. This new species is similar to A. chinensis, but differs from it due to the presence of a green young rachis of rhizomatous leaf, dense whitish long glandular hairs and sparse brownish long non-glandular hairs on the young rachis, dense brownish long glandular hairs of 1.5 to 2.7 mm length on the mature inflorescence, ovateelliptic terminal leaflet, weakly undulated margin of leaf adaxial epidermal cell, and a stomatal apparatus of larger size and lower density on the leaf abaxial epidermis. These differences between A. uljinensis and A. chinensis have been summarized in Table 1    Distribution and habitat. Currently, A. uljinensis is observed only in the central regions of South Korea, including Gangwon-do (Pyeongchang-gun, Samcheoksi, Gangneung-si) and Gyeongsangbuk-do (Uljin-gun). The species is found either in shady forests or on slopes near streams.

Astilbe uljinensis
Phenology. Flowering occurred between early June and late August. Fruiting occurred between July and October.
Conservation status. At present, the known habitats of this new species are not being protected legally. In addition, since this species generally grows near streams, it is vulnerable to flooding. Previously, up to 10-20 individuals were found by the authors in some of this species' populations. During the course of the present study, only a very small number of individuals were observed in some of the known habitats, probably indicating a decline in the plant population. However, the conservation status for the known populations has not been thoroughly investigated to date. Therefore, in accordance with the IUCN (2019) red list criteria, we suggest that this species should be treated as Data Deficient (DD).  Han & G.H.Kim, 130711-2 (CBU!).

Discussion
In the present study, the morphology of the trichomes on the plant body was studied extensively (Table 1; Fig. 3). When compared with the most similar Astilbe species, A. chinensis, this undescribed plant has only brownish long glandular hairs on its inflorescence (Fig. 3E), while A. chinensis has both brownish long glandular hairs and brownish short glandular hairs on it (Fig. 3F). In addition, the undescribed species has long whitish glandular hairs and long brownish non-glandular hairs on the young rachis of the rhizomatous leaves (Fig. 3B), while A. chinensis has short and long whitish glandular hairs, and long whitish non-glandular hairs on it (Fig. 3D).
The shape of the leaf epidermal cells was also distinct in this undescribed plant. The adaxial epidermal cells of the new species had weakly undulated margins, while those of A. chinensis had violently undulated margins (Fig. 4). The stomatal apparatus on the abaxial leaf epidermis of the new species was slightly larger than that of A. chinensis (Table 1), and the density of the stomatal apparatus was lower in the new species compared to A. chinensis (Table 1). The shape of the terminal leaflet was ovate-elliptic in the new species (Fig. 2E, F), differing from the rhomboid-elliptic leaflet of A. chinensis.  The present study revealed that the morphology of the trichomes on the plant body, and their density, could be important characteristics for the identification of the newly described species, at the genus level. In addition, the geographical distribution of the undescribed plant is restricted to the central regions of South Korea, Gangwon-do and Gyeongsangbuk-do, which is also distinct compared to the distribution of other Astilbe species. From both the morphological observation and the recognized distribution patterns, we conclude that the previously undescribed plant should be treated as a new species. In this new species, both the macro-morphological and the micro-morphological characteristics are potentially important taxonomic keys for its identification.