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Dryopteris sukungiana, a new tetraploid fern species of Dryopteridaceae in Yunnan, Southwest China, is described and illustrated. Morphologically, D. sukungiana belongs to the D. sparsa complex but is unique in spreading blackish brown scales on the stipe, glandular hairs and small fibrillose scales on the abaxial surface of the lamina. Phylogenetic analyses show that D. sukungiana is of hybrid origin; its paternal parent is the Sino-Himalayan D. sparsa, and its maternal parent might be an undetected diploid species closely related to the Sino-Japanese D. sparsa.

The Adiantum pedatum complex is disjunctly distributed in North America and eastern Asia. In this study, we carried out a detailed morphological study based on 137 specimens representing the biogeographic diversity of this complex. The sequences of eight chloroplast markers of 35 samples were analyzed with maximum likelihood and Bayesian inference. The morphological and phylogenetic analyses support the recognition of a new species of the A. pedatum complex from Japan. We propose the new species as A. japonicum based on the examinations of specimens from Japan and the comparative analyses of the whole complex. This new species can be distinguished from A. pedatum by the erect rhizome and shows significant molecular differences from other species in this complex. A taxonomic description with detailed morphological characters of the new species is presented.

Dryopteris sukungiana Z. Y. Zuo, sp. nov. (Figs. 1 & 2), in Chinese ���Dzfl����� (y��n n��n l��n m��o ju��). Type:��� CHINA. Yunnan: Maguan, 103��59��� E / 22��50��� N, 1950 m alt., 22 June 2021, Z. Y. Zuo 4660 (holotype KUN-1519949; isotypes HITBC-0061304, KUN-1519950, PE-02354809). Diagnosis:��� The scales of Dryopteris sukungiana are blackish brown and spreading (Fig. 3E), which is different from all other species in the D. sparsa complex (Fig. 3D, 3F). Dryopteris sukungiana is similar to the ���typical��� Sino-Himalayan D. sparsa with erect rhizomes, deltoid or pentagonal tripinnatifid to tripinnate lamina, basal pinnae abruptly broadened toward the base (Fig. 3A, 3B), but differs in having glandular hairs and small fibrillose scales on the abaxial surface of the lamina and the indusia (Fig. 3G, 3H). It resembles the Sino-Japanese D. sparsa in the catadromous pinnules of the second pair of pinnae and glandular hairs on the indusia and the abaxial surface of the lamina (Fig. 3H, 3I); however, the lamina of the Sino-Japanese D. sparsa is ovate-deltoid, and the basal pinnae are gradually broadened (Fig. 3C). Dryopteris sukungiana also looks like D. angustipalea Darnaedi, M. Kato & K. Iwats. (1989a: 308); however, the latter is endemic to Indonesia, and in which the lamina is ovate-deltoid, the basal pinnae are gradually broadened toward the base, rachis and costae are glabrous. Plants 30���60 cm tall. Rhizome erect, up to 8 cm long and 2 cm in diameter, clothed with blackish brown, linear- or ovate-lanceolate, spreading, entire scales. Stipe slightly shorter than lamina, ca. 17���38 cm, covered with glandular hairs when young, brown at base, with blackish brown linear- or ovate-lanceolate, spreading, entire, scales. Lamina papery, glossy, deltoid or pentagonal, ca. 26���53 �� 18���35 cm, tripinnatifid to tripinnate, base not narrowed, apex acuminate, with glandular hairs on abaxial surface. Pinnae 9���17 pairs, deltate-lanceolate, up to 16 �� 6 cm, apex caudate-acuminate; Basal 1���3 pairs opposite and alternate upward, oblique, stalked approximately 1���2 cm. Basal pinnae abruptly broadened toward the base. Pinnules 9���23 pairs, margin serrate to lobed, opposite at base and alternate upward, lanceolate to rounded, base broadly cuneate, asymmetrical, apex obtuse to truncate. Basal basiscopic pinnules of basal pinnae longest, ca. 5���8 �� 2���3 cm, base widest, 2-pinnate. Pinnules of the second pair of pinnae catadromous. Rachis and costa clothed with glandular hairs and small fibrillose scales. Veins pinnate, forked, distinct on both surfaces. Sori close to costa on pinnules, with a wide sterile belt on both sides of costa distal to sori. Indusia orbicularreniform, entire, with glandular hairs. Reproductive mode and ploidy level: sexual tetraploid. Additional specimens examined (paratypes): ��� CHINA. Yunnan: Baoshan, Z. Y. Zuo 1615 & 4937; Cangyuan, Z. Y. Zuo 2862; Kunming, J. M. Lu 179; Longling, X. Cheng et al., FB581; Tengchong, Z. Y. Zuo 1498, 1520 & 4949. Ecology and geographical distribution: ��� Dryopteris sukungiana was found in mountain forests at alt. 1900��� 2450 m in the central, southern, and southwestern parts of Yunnan Province, China, and perhaps in other neighboring areas. Etymology:��� In honor of late Prof. Su-Gong Wu (Su-Kung Wu in Wide-Giles transliteration) (1935-2013), for his contributions to the taxonomic studies on ferns in China, and especially the contributions to collections and studies on the ferns of the Qinghai-Tibet Plateau. He also edited some sections of Dryopteris in Flora Reipublicae Popularis Sinicae and Flora of China., Published as part of Zuo, Zheng-Yu, Lu, Jin-Mei, Wang, Yue-Hua & Li, De-Zhu, 2022, Dryopteris sukungiana (Dryopteridaceae), a new species of the D. sparsa complex from Southwest China, pp. 256-266 in Phytotaxa 533 (5) on pages 260-264, DOI: 10.11646/phytotaxa.533.5.2, http://zenodo.org/record/6144962

Additional file 1. Information of Voucher specimens, the characteristics, and GenBank accession numbers of newly generated plastomes in this study.

Additional file 2. Maximum likelihood (ML) phylogeny of Polypodiales suborder Dennstaedtiineae based on CDS data set.

Additional file 3. Bayesian inference (BI) phylogeny of Polypodiales suborder Dennstaedtiineae based on CDS data set.

Adiantum japonicum T. Zhao, Z. Y. Zuo, J. Wen & Jin Mei Lu, sp. nov., Fig. 3. Type:��� JAPAN. Central Honshu: Kyoto Pref., Ukyo-ku, Nakagawa, ca 200 m alt., 2 June 1978, Y. Tateishi et J. Murata 4141 (holotype: KUN!; isotypes: TNS!, NCU!, WAG!) Diagnosis: ��� Adiantum japonicum is similar to A. pedatum, but it is distinguished from the latter by the erect rhizome and clustered fronds. Plants deciduous, 40���60 cm tall. Rhizome erect; scales bronzy deep yellow, broadly lanceolate, margins entire. Fronds lax-arching, closely spaced clustered; petiole 1���2 mm diam., castaneous, glabrous. Lamina pedately dichotomous, 15���32 �� 15���35 cm, glabrous; pinnae 1-pinnate distally. Pinnae 3���8 pairs, oblong-lanceolate; inner pinnae up to 15���32 �� 1.5���4.5 cm, outer pinnae slightly shorter; rachises castaneous, glabrous. Pinnules 17���45 pairs per pinna, alternate, obliquely spreading, herbaceous, green, both surfaces glabrous, oblong, ca. 3 times as long as broad; basal pinnules slightly smaller, flabellate or semi-orbicular, with longer petiolule; basiscopic margin straight; acroscopic margin lobed, lobes separated by 0.3���1 mm incisions, margins of lobes crenulate or crenate-denticulate; petiolule 0.6���1.8 mm long, castaneous, glabrous. Sori 4���6 per pinnule, horizontally attached in shallow sinuses; false indusia grayish green to dark brown, transversely oblong, ca. 2.2 (1.5���3.6) mm �� 0.8 (0.5���1) mm, glabrous. Spores yellow or yellowish brown, tetrahedric, trilete, 40���50 ��m diam., scabrate. Habitat and distribution: ��� In forests: 100���1110 m. Hokkaido, Honshu, and Shikoku of Japan. Additional specimens examined:��� JAPAN. Hokkaido: Nakato N. 2162 (TNS!). Honshu: This new species is distributed throughout Honshu (see Appendix 1). Shikoku (rare): Ehime, Watanabe K. (TNS!). Additional notes: ��� Adiantum japonicum has long been identified as A. pedatum. There are significant molecular differences between the Japanese lineage and other members of the A. pedatum complex. The Japanese samples were resolved as monophyletic and being sister to a clade formed by A. pedatum, A. aleuticum, and A. viridimontanum in our phylogenetic analyses. We checked the specimens and collected morphological data from the entire distribution area of the A. pedatum complex. The results showed that, compared with the North American A. pedatum, the Japanese samples have an erect rhizome (vs. creeping rhizome) and clustered leaves (vs. distant leaves). Therefore, we segregate the Japanese lineage from A. pedatum as a new species A. japonicum, and recognize A. pedatum as restricted to deciduous woodlands in eastern North America. So far, we have not detected significant morphological differences between the North American A. pedatum and Chinese and Himalayan ��� A. pedatum ���. We will conduct further comparative morphological and phylogeographic analyses of the Chinese and Himalayan ��� A. pedatum ��� with the North American and Japanese counterparts in our future efforts. Previous chromosomal counts showed that hybridization and polyploidy are frequent in the A. pedatum complex, and it has a base chromosome number of x = 29 and x = 30, and six cytotypes (two diploids 2 n = 58 and 2 n = 60, one triploid 2 n = 87, and three tetraploids 2 n = 116, 2 n = 118, and 2 n = 120) (Paris & Windham 1988, Nakato & Kato 2005). The Japanese populations have four cytotypes (2 n = 58, 2 n = 60, 2 n = 118, and 2 n = 120), of which diploids of 2 n = 60 are widely distributed in Japan, diploids of 2n=58 have been found only in eastern Hokkaido, and two tetraploids 2 n = 118 and 2 n = 120 are rare in Japan (Nakato & Kato 2005). Our phylogenetic analyses showed that the lineage into which the diploid 2 n = 60 (Nakato N. 2162 from Hokkaido, Japan) clustered is a sister group of the other lineages of this complex, and the rest of the Japanese cytotypes were clustered with Chinese lineages. The samples of A. japonicum were collected widely throughout Japan (e.g., Hokkaido, Nagano, Osaka, Shikoku, and Shizuoka), and we speculate that the newly described A. japonicum is a diploid of 2 n = 60. The present study implied that there may be more than one cryptic species remaining to be described in East Asia. We will carry out further studies on chromosomal survey and morphological and molecular systematic studies to resolve the species delimitations of this biogeographically significant species complex (Wen 2001; Wen et al. 2016; Zhou et al. 2020)., Published as part of Zhao, Ting, Zuo, Zheng-Yu, Ebihara, Atsushi, Nakato, Narumi, Soejima, Akiko, Li, De-Zhu, Wen, Jun & Lu, Jin-Mei, 2021, Adiantum japonicum, a new species of the Adiantum pedatum complex (Pteridaceae) from Japan, pp. 1-14 in Phytotaxa 525 (1) on pages 7-8, DOI: 10.11646/phytotaxa.525.1.1, http://zenodo.org/record/5681778, {"references":["Paris, C. A. & Windham, M. D. (1988) A biosystematic investigation of the Adiantum pedatum complex in eastern North America. Systematic Botany 13: 240 - 255. https: // doi. org / 10.2307 / 2419103","Nakato, N. & Kato, M. (2005) Cytogeography of the Adiantum pedatum Complex (Pteridaceae, Subfamily Adiantoideae). Acta Phytotaxonomica et Geobotanica 56: 85 - 96. https: // doi. org / 10.18942 / apg. KJ 00004622915","Wen, J. (2001) Evolution of eastern Asian - eastern North American biogeographic disjunctions: a few additional issues. International Journal of Plant Sciences 162 (S 6): S 117 - S 122. https: // doi. org / 10.1086 / 322940","Wen, J., Nie, Z. - L. & Ickert-Bond, S. M. (2016) Intercontinental disjunctions between eastern Asia and western North America in vascular plants highlight the biogeographic importance of the Bering land bridge from late Cretaceous to Neogene. Journal of Systematics and Evolution 54: 469 - 490. https: // doi. org / 10.1111 / jse. 12222","Zhou, W., Xiang, Q. - Y. (J.) & Wen, J. (2020) Phylogenomics, biogeography, and evolution of morphology and ecological niche of the eastern Asian - eastern North American Nyssa (Nyssaceae). Journal of Systematics and Evolution 58: 571 - 603."]}