﻿Ranunculusmaoxianensis (Ranunculaceae), a new species from northwestern Sichuan, China, with an emended description of R.chongzhouensis, the putative closest ally of the new species

﻿Abstract Ranunculusmaoxianensis (Ranunculaceae), a new species from Jiuding Shan in Maoxian county, northwestern Sichuan province, China, is here illustrated and described. The species is morphologically similar to R.chongzhouensis, a species also occurring in Sichuan, in having reniform leaves and puberulous receptacles, carpels and achenes, but differs by having leaves adaxially puberulous with shorter appressed hairs 0.16‒0.28 mm long (vs. longer appressed hairs 0.55‒0.85 mm long), larger flowers (1.8‒2 cm vs. 1.4‒1.6 cm in diameter), larger (8‒10 × 5.5‒6.5 mm vs. 6‒7 × 4.5‒5 mm) and widely obovate petals (vs. obovate), more numerous stamens (35‒55 vs. 12‒18), and subglobose gynoecium and aggregate fruit (vs. ellipsoid). The two species are also different in chromosome number and chromosome morphology. Ranunculuschongzhouensis has a karyotype of 2n = 2x = 16 = 10m + 6sm while R.maoxianensis has a karyotype of 2n = 4x = 32 = 16m + 16sm. An emended description of R.chongzhouensis is provided, and its geographical distribution is largely extended.

During a botanical expedition to the Hengduan Mountains region from June to August 2022 for the first author's Ph.D. dissertation project, we discovered an unusual population (Figs 1, 2) of Ranunculus on Jiuding Shan in Maoxian county, northwestern Sichuan province, China. The plants are somewhat similar to R. chongzhouensis W.T. , a species also occurring in Sichuan, in having reniform leaves and puberulous receptacles, carpels and achenes, but differ by an array of characters, such as the length of hairs on the adaxial side of leaf blades, size of flowers, size and shape of petals, number of stamens, and shape of the gynoecium and aggregate fruit. Moreover, our chromosomal examination revealed that the Maoxian population in question has a chromosome number of 2n = 16 (Fig. 11A), while R. chongzhouensis has a chromosome number of 2n = 32 (Fig. 11B). Therefore, we determined that this population represents a hitherto undescribed species, which we describe as R. maoxianensis below. Furthermore, we found that R. chongzhouensis, the putative closest ally of R. maoxianensis, is much more widely distributed than documented before and that its original description is not complete, lacking a description of root and floral characters, with the description of indumentum of leaf blades, receptacles and achenes being also incorrect. Based on our critical observations of herbarium specimens and living plants in the wild, the description of this species is here emended. We also largely extended its geographical distribution.

Materials and methods
For morphological comparison, we critically examined specimens or high-resolution specimen images of Ranunculus at CDBI, KUN, PE, and WCSBG (acronyms according to Thiers 2022). We also observed living plants in three populations of R. chongzhouensis from Sichuan and one population of the new species R. maoxianensis (Table 1) at flowering and fruiting time (June to July). We observed characters of roots, stems, leaves, pedicels, flowers, receptacles, petals, stamens, gynoecium, carpels, aggregate fruit and achenes, paying special attention to the indumentum of basal leaves, size of flowers, size and shape of petals, number of stamens, and the shape of gynoecium and aggregate fruit.
For scanning electron microscopy (SEM), dry leaves were taken from herbarium specimens (Table 1) and mounted directly onto stubs using double-sided sellotape, gold-coated, and then observed and photographed under a JSM-6360LV scanning electron microscope.
For chromosomal examination, living plants of Ranunculus chongzhouensis from Xiling Xue Shan in Dayi, Sichuan, and R. maoxianensis from its type locality, i.e., Jiuding Shan in Maoxian, Sichuan (Table 1), were cultivated in pots in the experimental garden of South China Botanical Garden, Chinese Academy of Sciences. Root tips were pretreated in 0.1% colchicine for 2.5 h, fixed in Carnoy I (glacial acetic acid: absolute ethanol = 1: 3), then macerated in 1 M HCl at 37 °C for 45 min, and stained and squashed in Carbol fuchsin. Karyotype formulas were based on the data of measurements of mitotic-metaphase chromosomes of three cells taken from photographs. We followed the acronyms proposed by Levan et al. (1964) to describe the karyotypes.
Our chromosomal examination reveals that Ranunculus maoxianensis is a diploid species with 2n = 2x = 16 = 10m + 6sm (Fig. 11A, C), while R. chongzhouensis is a tetraploid with 2n = 4x = 32 = 16m + 16sm (Fig. 11B, D). This result lends strong support to the description of R. maoxianensis as a new species.  Our literature consultation and critical observations on herbarium specimens and living plants in the wild reveal that Ranunculus chongzhouensis, the putative closest ally of R. maoxianensis, lacks the description of root and floral characters, with the description of indumentum of leaf blades, receptacles and achenes by Wang (2015) being also incorrect. Wang (2015) (Figs 4-9). In addition, we found that the indumentum on the abaxial side of the leaf blades of R. chongzhouensis is somewhat variable between populations. The leaf blades are often abaxially glabrous (Figs 4E, 6E), but sometimes abaxially puberulous (Fig. 8E).
Etymology. The specific epithet refers to the type locality of the new species, i.e. Maoxian county in northwestern Sichuan province, China.
Phenology. Flowering from June to July; fruiting from July to August. Distribution and habitat. Ranunculus maoxianensis is currently known only from its type locality, i.e., Jiuding Shan in Maoxian county, northwestern Sichuan province, China (Fig. 13). It grows in Rhododendron forests at altitudes of 3200-3400 m above sea level.
Conservation status. Although Ranunculus maoxianensis is currently known only from its type locality, i.e., Jiuding Shan in Maoxian county, northwestern Sichuan province, China, our observations on living plants at its type locality revealed that this species is very common in Rhododendron forests at altitudes of 3200-3400 m above sea level. It should better be categorized as "Least Concern (LC)", following the IUCN Standards and Petitions Committee (IUCN 2022).

Ranunculus chongzhouensis
Phenology. Flowering from June to July; fruiting from July to August. Distribution and habitat. Ranunculus chongzhouensis is distributed in Baoxing, Chongzhou, Dayi, Heishui, Luding, Songpan, and Xiaojin in Sichuan province, China (Fig. 13). It grows in forests or meadows at elevations of 2900-4150 m above sea level. Additional