﻿Hydrangeaxinfeniae (Hydrangeaceae), a new species from Sichuan, China

﻿Abstract Hydrangeaxinfeniae W.B.Ju & J.Ru, a new species of Hydrangeaceae from Sichuan Province, China, is described and illustrated. The new species belongs to Hydrangeasect.Dichroa (Lour.) Y.De Smet & Samain, with its distinctive characteristic being the nearly superior ovary. It shares morphological similarities with H.yaoshanensis (Y.C.Wu) Y.De Smet & C.Granados, but can be distinguished by its hirsute trichomes densely covered on the branchlets, leaves, peduncles and pedicels, broadly elliptic to rectangular-elliptic leaf blade with nearly rounded base, coarse teeth leaf margins, 3–4 pairs of lateral veins, corymbose cyme with few and loose branches, lanceolate bract, the calyx tube and lobes margin with sparsely hirsute trichomes, adaxially glabrous and abaxially sparsely hirsute petal, outer whorl filaments are linear, inner ones are awl-shaped, glabrous styles, and the nearly superior ovary. H.xinfeniaesp. nov. currently known from only three relatively small populations of the type locality, and its conservation status is assessed as Data Deficient (DD).

Hydrangea sect.Dichroa (De Smet et al. 2015) comprises 12 species, widely distributed in the tropical and subtropical regions of Southeast Asia, with only a few species extending to Pacific islands.In China, there are six species of this section, distributed from the southwestern to eastern regions (Huang 1987;Huang et al. 1995;Wei and Bartholomew 2001).In recent years, new species from this section have been discovered in China (Huang et al. 2018;Deshmukh and Shende 2021).
During field investigations in Huagaoxi National Nature Reserve of Shuwei Town, Xuyong County, Sichuan Province, an unknown population of Hydrangea was discovered.After conducting a comprehensive review of relevant taxonomic literature (Chun 1954;Huang 1987;Huang et al. 1995;Wei and Bartholomew 2001;Jacobs 2010;Huang et al. 2018) and meticulously examining voucher specimens from various herbaria (A, B, C, CAS, CDBI, E, IBK, IBSC, P, PE, K, KUN, L, NYBG, US), we have identified that it represents a new species within Hydrangea sect.Dichroa, exhibiting morphological similarity with H. yaoshanensis (De Smet et al. 2015).In this study, we provide a detailed morphological characterization of this species based on our field observations and a thorough examination of the holotype specimen, and describe it as a new species.

Material and methods
The voucher specimens of the new species in this study were collected from the type locality, Huagaoxi National Nature Reserve, and are deposited in CDBI and KUN.The morphological description of characteristics of the new species was conducted through both living plants in the field and voucher specimens.The morphological measurements of the new species were based on living plants.We examined available online specimen images of Hydrangea sect.Dichroa species stored in A, B, C, CAS, CDBI, E, IBK, IBSC, P, PE, K, KUN, L, NYBG, and the US through the Chinese Virtual Herbarium (https://www.cvh.ac.cn/) and JSTOR Global Plants (https://plants.jstor.org/).Additionally, we compared the morphological characteristics of the new species with those of similar species, relying on online voucher specimen images and published literature (Huang 1987;Huang et al. 1995;Huang et al. 2018;Deshmukh and Shende 2021).Diagnosis.Hydrangea xinfeniae can be distinguished from the morphologically similar species H. yaoshanensis by the presence of densely hirsute trichomes on branchlets, leaves, peduncles and pedicels; leaf blades that are broadly elliptic to rectangular-elliptic with a nearly rounded base and coarse teeth along the leaf margin, lateral veins 3-4 on each side of the midvein; a corymbose cyme with few, loosely arranged branches and lanceolate bract; calyx tube sparsely covered with hirsute trichomes, with only the edges of the lobes bearing such hairs; a glabrous adaxial surface of the petals, while the abaxial surface is adorned with scattered hirsute trichomes; outer whorl filaments are linear, inner ones are awl-shaped; styles are glabrous, and a nearly superior ovary.
Phenology  Preliminary conservation assessment.Based on the currently available survey data, only three relatively small populations have been discovered in Huagaoxi National Nature Reserve.Our knowledge regarding the status and distribution range of populations outside this area is limited.According to IUCN red list categories and criteria (IUCN 2022), the conservation status of the new species is temporarily assessed as Data Deficient (DD) due to insufficient avail-  able data.Further comprehensive surveys in similar environments and neighboring regions are necessary to provide a better assessment of the distribution and abundance of this species.

Discussion
Hydrangea sect.Dichroa is distinguished from related sections within Hydrangea by characteristics such as being an erect shrub, inflorescences with all fertile flowers, calyx lobes never petaloid, and fruit as berry.Based on a series of morphological characteristics, including shrub, opposite leaves, bisexual and isomorphic flowers, an inverted conical calyx tube attached to the ovary, petals with slightly inwardly curled tips forming hooks, outer whorl filaments are linear, inner whorl filaments awl-shaped, and separated styles, Hydrangea xinfeniae sp.nov. is classified within the Hydrangea sect.Dichroa (Huang 1987;Huang et al. 1995;Wei and Bartholomew 2001;De Smet et al. 2015).Species within Hydrangea sect.Dichroa were previously treated as members of the genus Dichroa Lour.(Loureiro 1790) (Huang et al. 1995;Huang et al. 2018;Deshmukh and Shende 2021).Among the aforementioned species distributed in China, H. xinfeniae sp.nov.exhibits morphological resemblances to H. yaoshanensis in having the shape of leaf blade, corymbose cymose, inverted conical calyx tube and spherical-shaped berry.However, H. xinfeniae sp.nov.can be distinguished by its dense hirsute trichomes on branchlets, leaves, peduncles, and pedicels, as well as its broadly elliptic to rectangular-elliptic leaf blades, nearly entire circular leaf basis, coarse teeth on the leaf margin, 3-4 lateral veins on each side, corymbose cyme with sparsely and loosely branched, calyx tube with sparse hirsute trichomes, lobes with sparse hirsute trichomes only on the margins, glabrous on the inner surface of the petals, scattered hirsute trichomes on the outer surface, outer whorl filaments are linear, inner ones are awl-shaped, styles are glabrous, and nearly superior ovary.Notably, the nearly superior ovary is a unique characteristic of H. xinfeniae sp.nov.compared to other species within Hydrangea sect.Dichroa.For a detailed comparison of features, please refer to Table 1.

Figure 1 .
Figure 1.Hydrangea xinfeniae W.B.Ju & J.Ru, sp.nov.A plant B leaf adaxial C twig D a branch with inflorescence E flower F petal G stamen H berry. Illustration drawn based on living plants (flower and berry) combined with specimens from the holotype by Zhenlong Liang.

Figure 3 .
Figure 3. Hydrangea xinfeniae W.B.Ju & J.Ru, sp.nov. in the wild A habit B a branch with inflorescence C fruiting branch.

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Flowering from May to June; Fruiting from July to October.Distribution and habitat.Hydrangea xinfeniae sp.nov. is found in its type locality, the Huagaoxi National Nature Reserve in Shuiwei Town, Xuyong County, Sichuan Province, China.It grows on moist soils under the broadleaved forest at an elevation of 1200-1300 meters.Etymology.The species epithet xinfeniae is in honor of Prof. Xinfen Gao, a distinguished female botanist who made significant contributions to the plant diversity survey of Huagaoxi National Nature Reserve.

Table 1 .
The comparison of morphological characters of Hydrangea xinfeniae sp.nov.and H. yaoshanensis.