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PhytoKeys 148: 93-104 (2020)
& doi: 10.3897/phytokeys. 148.5 1589 46Ph y toKe y S
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Athyrium bipinnatum K.Hori (Athyriaceae), a new cornopteroid fern from Japan
Kiyotaka Hori!
| The Kochi Prefectural Makino Botanical Garden, Kochi, Japan
Corresponding author: Kiyotaka Hori (khori@makino.or.jp)
Academic editor: B. Leén | Received 28 February 2020 | Accepted 7 April 2020 | Published 26 May 2020
Citation: Hori K (2020) Athyrium bipinnatum K.Hori (Athyriaceae), a new cornopteroid fern from Japan. PhytoKeys 148: 93-104. https://doi.org/10.3897/phytokeys. 148.51589
Abstract
I describe Athyrium bipinnatum sp. nov. and discuss morphological differences between closely related species. Ihe new species is endemic to Japan, occurring on the islands of Honshu, Kyushu, and Shikoku. Based on the criteria of the International union for conservation of nature and natural resources, this new
species is here considered endangered.
Keywords
Athyrium, Cornopoteris, Japan, new species
Introduction
Cornopteris Nakai is a small Asian (Himalayas, East and Southeast Asia) genus of ter- restrial ferns that used to be recognized by many pteridologists (e.g., Nakai 1930; Ito 1939; Ching 1945; Holttum 1958; Tagawa 1959; Kato 1977, 1979), on the basis of fleshy stipes, corniculate leaf axes, and exindusiate sori.
Regarding its phylogenetic relationships, Ching (1945) regarded it to be “a little offshoot of the exindusiate Diplazium.” Based on the presence of J-shaped sori in some species of Cornopteris, as well as on stipe features and spinulose midribs of the laminae, Kato (1977) concluded that Cornopteris was actually more closely related to Athyrium than to Diplazium. Serizawa (1981) agreed with Kato’s conclusion and subsumed Cor- nopteris in Athyrium. To corroborate his taxonomic decision of lumping the two gen- era, Serizawa (1981) also highlighted the existence of natural hybrids between them.
Copyright Kiyotaka Hori. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
94 Kiyotaka Hori / PhytoKeys 148: 93-104 (2020)
These are: Athyrium x cornopteroides Sa.Kurata (Cornopteris opaca (D.Don) Tagawa x Athyrium kuratae Seriz.), Athyrium x glabrescens Seriz. (Cornopteris decurrentialata (Hooker) Nakai x A. kuratae), and Athyrium x petiolatum Sa.Kurata (C. opaca x Athy- rium yakusimense Tagawa). Sano et al. (2000) showed monophyly of the genus Cor- nopteris based on rbcL gene phylogeny, but Adjie et al. (2008) showed A. distentifolium placed in the same clade of Cornopteris in rbcL phylogeny. Therefore, Cornopteris spp. have been classified in Athyrium (Athyriaceae) based on DNA phylogenies (Rothfels et al. 2012, PPG I 2016, Ebihara 2017). However, Moran et al. (2019) distinguished the genus Cornopteris from Athyrium based on plastid DNA phylogeny. In the present study, Cornopteris spp. are treated as members of Athyrium.
Cornopteroid species of the genus Athyrium are mainly distributed in the Himala- yas, in East and Southeast Asia. The exact number of species is unknown. Kato (1979) recognized nine species of cornopteroid ferns, whereas Zhaorong and Kato (2013) recognized 16 species only in China.
The following is a brief history of the classification of one Athyrium species, namely Athyrium x christensenianum (Koidz.) Seriz., which is partly the focus of the present study. Athyrium x christensenianum was first described by Koidzumi (1924) as Diplazium christensenianum Koidz., from Jeju (Quelpaert)-Island, South Korea (Fig. 1). Kato (1979) synonymized Cornopteris hakonensis Nakai, from Hakone, Ja- pan (Nakai 1930, Fig. 2) under Cornopteris christensenianum. Subsequently, Serizawa (1981) transferred it to Athyrium and created the nothospecific name A. x christense- nianum. ‘the hybrid origin of this species has been pointed out by many authors (Kurita 1964, Hirabayashi 1970, Kato 1979, Park and Kato 2003). According to these authors (Kurita 1964, Hirabayashi 1970, Kato 1979, Park and Kato 2003), this is a triploid “species” that has resulted from a cross between diploid sexual Athyrium crenulatoserrulatum Makino and tetraploid sexual Athyrium decurrentialatum (Hook.) Copel. It remains unclear whether A. x christensenianum is merely a sterile hybrid or an independent fertile species. Kato (1979) categorized it as being of a “hybrid ori- gin species” between A. crenulatoserrulatum Makino and A. decurrentialatum because it has intermediate morphological characteristics between these two species such as serrated segments, subcartilaginous margins of the blade, and elliptical sori. On the other hand, Serizawa (1981) treated this “species” as a sterile “hybrid.” The present study agrees with the treatment of A. x christensenianum by Serizawa (1981).
Recent studies have reported complicated relationships in the A. x christenseni- anum complex. First, Hori and Murakami (2019) reported a tetraploid sexual cytotype of A. x christensenianum (as the independent species A. christensenianum). Subsequent- ly, Hori (2019) reported that tetraploid sexual A. x christensenianum had one allele of A. crenulatoserrulatum and one of A. decurrentialatum, each in the biparental inherited nuclear DNA marker of the gene AKI. He also found that triploid A. x christenseni- anum had two alleles of A. crenulatoserrulatum and one allele of A. decurrentialatum. Therefore, he suggested two hypotheses: (1) tetraploid sexual A. x christensenianum originated from the hybridization of diploid sexual A. crenulatoserrulatum with an an- cestral or extinct diploid A. decurrentialatum; and (2) triploid A. x christensenianum originated from the hybridization of diploid sexual A. crenulatoserrulatum and tetra-
Athyrium bipinnatum from Japan 95
ornopteris chr fide Tagawa, Acta P L95a AGBoe
Crmeptinis opace (Pon) Tag ann
Det. M, Tagawa AVON KYO 00019813 * Herb. Bot. Inst. Sci. Coll. Imp. Univ. Kyoto.
sce DME MM TR pA acs Mense Z Anni 19323.
PLANTAE FAURIEAWAE Herb, Bot. Inst. Sci, Facult. Imp. Unbe Vivo Wid ee at, AR He AFT URBAIN FAURLE
FAURIE, No. Nom. Jap.. Loc., Hab,
A ALOE b AOE : » PLANTA CORTANIVA,
seossee., “dense
Figure |. Holotype of Diplazium x christensenianum Koidz.
ploid sexual A. x christensenianum (Fig. 3). In the present study, the unclear taxonomy of A. x christensenianum was clarified by describing tetraploid sexual A. x christenseni- anum as a new species: Athyrium bipinnatum from Japan (Fig. 3).
96 Kiyotaka Hori / PhytoKeys 148: 93-104 (2020)
¢
LlerbViimeiversitatis Imperialis Tokyoensts. Pot i El kK Bw A A AR WE &
Figure 2. Holotype of Cornopteris hakonensis Nakai.
Athyrium bipinnatum from Japan 97
A. X christensenianum
3x ie Undetected A. crenulatoserrulatum A. decurrentialatum 2x 2X
A. bipinnatum 4x
Figure 3. Relationships of Athyrium bipinnatum and its related species.
Materials and methods
First, the morphological characteristics of a tetraploid sexual specimen of Athyrium bipin- natum (Hori 2974) and the sexual specimens (Hori 2975, 2976) described by Hori (2019) were examined. Iwo type specimens of A. christensenianum, deposited at KYO (as Dipla- zium christensenianum, Fig. 1) and TI (as Cornopteris hakonensis, Fig. 2), were also exam- ined. Furthermore, based on morphological characteristics, more specimens of A. bipin- natum were identified at MAK and MBK, and from online images at PE herbarium (PE: http://pe.ibcas.ac.cn/en/), Taiwan Forestry Research Institute herbarium (TAIF: http:// taif.tfri.gov.tw/search.php), Collection Database of Specimens and Materials (TNS: http://db.kahaku.go.jp/webmuseum/), and from those in JSTOR Global Plants (https:// plants.jstor.org/) and the Global Biodiversity Information Facility (GBIF: https://www. gbif.org). Additional samples were also collected in the field and cultivated samples were taken from Koishikawa Botanical Garden of Tokyo University. For the conservation as- sessment, the area of occupancy (AOO) and extent of occurrence (EOO) were estimated using GeoCAT (Bachman et al. 2011), with the default settings for grid size applied. The morphology of scales and spores was observed using a KEYENCE VHX-D500.
Taxonomic treatment
Athyrium bipinnatum K.Hoti, sp. nov. urn:lsid:ipni.org:names:77209707-1 Figure 4
Diagnosis. A. bipinnatum is similar to A. x christensenianum (Koidzumi 1924, Nakai 1930, Kato 1979, Serizawa 1981) as it has serrated pinnae and exindusiate sori. How- ever, A. bipinnatum has mote short stipes (10—20 cm long), smaller blades (20-40 cm
98 Kiyotaka Hori / PhytoKeys 148: 93-104 (2020)
x 14-20 cm), 2-pinnate pinnae in the middle of the blades, and fronds with dark green adaxial surfaces. In contrast, A. x christensenianum has longer stipes (25—40 cm long), larger blades (30-60 cm x 25—40 cm), 2-pinnate pinnatifid pinnae in the middle of the blades, and fronds with light green adaxial surfaces.
Type. Japan. Shikoku: Kochi prefecture, Ochi town, Mt. Yokogura, 33°32'11"N, 133°12'33"E, alt. 664 m, planted coniferous forest containing Cryptomeria japonica (Thunb. ex L.f.) D.Don, on soil, 29 Jun 2019, K. Hori 3277 (holotype: MAK466762; isotype: MBK).
Description. Terrestrial, summer green fern. Rhizomes creeping, occasionally 2-branched, stramineous, 8-15 x 0.8-1.5 cm, closely set with roots and persistent, densely clothed by old stipe bases, glabrous; fronds 1-3 per rhizome; stipes stramineous or slightly purple-red, 7—20 x 0.3—0.8 cm, sparsely clothed with stramineous to dark brown scales at the base (3-5 x 1-1.5 mm), lanceolate; blades dark green adaxially, 3-pinnatilobed at the base, 2-pinnate in the middle to upper section, pinnatifid at the apex, 20-40 x 14-20 cm, deltoid; rachises stramineous or slightly purple-red, dark brown, abaxially densely pilose, several projections 0.1 mm long on the adaxial surface at the bases of costae; pinnae 7-11 pairs, ascending, lanceolate, opposite from the base to the middle, alternate in the apex section of the blade, petioled (1-3 mm), sessile near the apex, closely spaced or overlapping, lowest pinnae slightly reduced, second lowest pair usually largest, 6-16 x 1.5—3 cm; pinnules, alternate on the basal and mid- dle sections of the blade, opposite on the apex of the blade, 10—20 pairs on the basal and middle sections of the blade, 8-10 pairs on the apex of the blade, reduced distally, ovate to lanceolate, shallowly serrate to lobed, margin subcartilaginous, vein-free, close to or reaching to the margin, 3—8 pairs in the middle lobe; the most basiscopic pinnules on the lowest pinnae clearly short, independent from the costa, 0.6—1 x 0.3-0.5 cm; sori tend to appear on the abaxial surface of the middle part of blades, short linear- or oblong-shaped, single, 1.5—5 mm long, on the apex or middle of veinlets, 1—5 per ul- timate segment, exindusiate, rather persistent; spores regular shaped, 64 regular-shaped spores per sporangium, fertile, ovoid, wrinkled, 42-54 um x 29-35 um, brown.
Etymology. Athyrium bipinnatum is named as a new species with bipinnate blades, which distinguish it from A. x christensenianum. This new species could be one of the parents of A. x christensenianum (Hori 2019).
Specimens examined. Japan. Honshu: Wakayama pref., Ito county, Kouya town, Mt. Kouyasann, Okunoin, alt. 800 m 7 Aug1954, coll. Md. Tagawa (NMNH 01529356, image!); loc. cit., ca. 800 m alt., 7 Aug 1954, coll. S.K. (MAK139!); doc. cit., on soil un- der planted coniferous forest containing C. japonica, alt. 800 m, 19 Aug 2019, K. Hori 3324 (MAK); Mie pref., Taki county, Miyagawa village, Doukuradani, alt. 1000 m, 6 Aug 1962, coll. ¥ Higuchi (TNS471359, image!); Nara pref., Tenkawa village, Mt. Gyojagaeridake, 15 Jul 1954, coll. Jwastuki (MAK 26788!); loc. cit., Dorokawa, Mita- rai valley, on soil under planted coniferous forest containing C. japonica, alt. 840 m, 20 Aug 2019, K. Hori 3326 (MAK). Shikoku: Kochi pref., Ochi town, Mt. Yokogu- rayama, 24 May 1956, Iwatsuki 1603 (PE, NUNH, MNHN, images! MAK! TI!); loc.
cit., on soil under planted coniferous forest containing C. japonica, alt. 800 m, 30 May
Athyrium bipinnatum from Japan 99
Figure 4. Athyrium bipinnatum K.Hori. A Habit B detail of adaxial pinnule C detail of abaxial pinnule D lower stipe scale E spore. A-E from the holotype (MAK466762) (illustration by K. Hori).
100 Kiyotaka Hori / PhytoKeys 148: 93-104 (2020)
2019, K. Hori 2974, 2975, 2976 (MAK, MBK); loc. cit., Aki county, Umaji village, Yanase, 19 June 1983, Y Koukami M83-163 (MBK); loc. cit., Muroto city, Kiragawa town, Nishinogawa river, 14 July 1976, Y Kazuoki 6614 (MBK). Kyushu: Fukuoka pref., Maebara town, Mt. Haganeyama, cultivated at Koishikawa Botanical Garden of Tokyo University, 17 June 2019, K. Hori 3268 (MAK); loc. cit., Kaho county, Chikuho town, Mt. Toishiyama, 17 July 1966, S. Tsutsui 2655 (TNS, image!); Oita pref., Take- da city, Kuju town, Mt. Kurodake, alt. 1140, 31 Aug 1997, S. Tsuji T]/-4346 (MAK).
Key to A. bipinnatum and closely related species in Japan
| Blades 2-pinnate pinnatifid in the middle section, yellowish green or light pieeiy Acacia ly OF secs cacncca constea ta esacaraseaaas cukd castenedas cofcahs descantedecits stecennaencta sts 2 - Blades 2-pinnate or 1-pinnate pinnatifid in the middle section, dark green ACVARTAM ace tor sta ie bueed tees ket enced tetas edeatemeed nated trae taedags Hationec tetecadetsine seecata tye 3 2 Blades yellowish green adaxially, pinnule in the middle section of blade deep- ly serrated on margin, spores regular... eee A. crenulatoserrulatum - Blades light green adaxially, pinnule in the middle section of blade shallowly serrated on margin, spores abortive... eeeeeeseeeeees A, x christensenianum 3 Blades 2-pinnate, pinnae straight, sori often single................ A, bipinnatum
- Blades 1-pinnate pinnatifid, pinnae curved to the apex, sori often lobed....... Euutede Mesto vaste tae paella valbanila test dlls talvante atts ra eh at A, decurrentialatum
195 40 VY VO BF 199-709 I =“) 1km —, % ON Pall
<A 145 140 145 150
Figure 5. Map showing the known distribution of Athyrium bipinnatum in Japan.
Athyrium bipinnatum from Japan 101
Distribution and ecology. Athyrium bipinnatum is known from the western part of Honshu, Shikoku, and Kyushu in Japan (Fig. 5). It was observed to grow on soil under planted coniferous forest containing Cryptomeria japonica at ca. 600-1100 m alt. This species is endemic to Japan.
Conservation status. [UCN Red List Category. Based on estimates from GeoCAT, the EOO of A. bipinnatum was 53,068 km’; however, this estimate should be smaller because this EOO contains an area of sea around Japan. Wild deer are known to eat A. bipinnatum (pers. obs.), so individual numbers within populations are currently decreasing and population reduction is occurring now. The known AOO of A. bipin- natum is 44 km°*. Based on the IUCN criteria (IUCN 2001, 2012), A. bipinnatum falls into the Endangered (EN) category. A formal evaluation of endangerment can be sum- marized by the following IUCN hierarchical alphanumeric coding system of criteria and subcriteria: EN Alabc+A2+C1+C2a(i).
Discussion
Athyrium x christensenianum was first described by Koidzumi (1924) as Diplazium christensenianum Koidz., from Jeju (Quelpaert)-Island, South Korea (Fig. 1). Subse- quently, Nakai (1930) described Cornopteris hakonensis Nakai, from Hakone, Japan (Fig. 2). I examined type material of both taxa, and found that they represent the same hybrid in having large size of stipes, blades, 2-pinnate pinnatifid pinnae in the mid- dle of the blades. Athyrium bipinnatum is distinguished from them in having shorter stipes, smaller blades, and by its 2-pinnate pinnae in the middle of the blades.
Athyrium bipinnatum is of hybrid origin between a diploid sexual A. crenulatoser- rulatum and an extinct or undetected diploid sexual A. decurrentialatum, and it is one of the parents of A. x christensenianum (Hori 2019, Fig. 3). Athyrium bipinnatum is clearly smaller than A. x christensenianum, and its morphological characteristics, which include 2-pinnate blades, are intermediate between those of A. crenulatoserrulatum and A. decurrentialatum (Figs 6, 7, Table 1). In contrast, the morphological characteristics of A. x christensenianum, which include 2-pinnate pinnatifid blades, are intermediate between A. bipinnatum and A. crenulatoserrulatum; the large size of this plant indi- cates this hybrid has heterosis. Athyrium bipinnatum and A. crenulatoserrulatum each have shorter stipes (10-20 cm and 20-30 cm long, respectively) and smaller blades (20-40 cm x 14-20 cm and 30-35 cm x 25-30 cm, respectively) than A. x christense- nianum (25-40 cm long stipes and 30-60 cm x 25—40 cm blades) (Table 1).
Contrary to the findings of the present study, Park and Kato (2003) reported reg- ular-shaped and germinative spores in their description of A. x christensenianum. Here, regular-shaped spores could not been found from dozens of A. x christensenianum her- barium specimens; however, regular-shaped spores were found from several specimens of A. bipinnatum, A. crenulatoserrulatum, and A. decurrentialatum. Therefore, it is pos- sible to speculate that Park and Kato (2003) perhaps confused the materials of these different species when they examined spore shape.
102 Kiyotaka Hori / PhytoKeys 148: 93-104 (2020)
B D
Figure 6. Abaxial surface of pinnule and sori of A Athyrium crenulatoserrulatum B Athyrium bipinnatum, C Athyrium x christensenianum D Athyrium decurrentialatum (illustration by K. Hori).
ea: 7. Wild plants of A i crenulatoserrulatum B Athyrium bipinnatum C Athyrium x chris-
tensenianum D Athyrium decurrentialatum.
Athyrium bipinnatum from Japan 103
Table |. Morphological comparison among A. bipinnatum and related species.
Characters A, bipinnatum A. x christensenianum | A. crenulatoserrulatum | A. decurrentialatum Stipe length (cm) 7-20 25-40 20-30 20-30 Pinna size (cm) 6-16x 1.5-3 15-30 x 5-9 10-20 x 5-8 8-15 x 3-5 Pinna stalk length (cm) 0.20.4 0.20.4 0.40.9 0-0.2 Blade size (cm) 15-40 x 14-20 30-60 x 25-40 30-35 x 25-30 20-35 x 15-25 Blade color adaxially dark green light green yellowish green dark green Blade division medially 2-pinnate 1-pinnate pinnatifid Pinnule division medially shallowly serrated deeply to shallowly deeply serrated shallowly serrated or
serrated entire
Sori single sometimes lobed single often lobed Spore shape regular irregular regular regular Spore size (tum) 42-54 x 29-35 30-44 x 22-39 25-37 x 16-20 27-45 x 21-35
In summary, the previously unclear taxonomy of A. x christensenianum was clari- fied in the present study by describing tetraploid sexual “A. x christensenianum” as the new species A. bipinnatum. Importantly, the conservation status analysis reported here suggests that A. bipinnatum may be endangered; thus, this study has relevance to the conservation of cornopteroid ferns.
Acknowledgments
I am grateful to Prof. M. Tamura and Prof. S. Fuse of Kyoto University (KYO), Prof. N. Murakami of Makino herbarium (MAK), and Dr. S. Nemoto of Tokyo University (TT) for showing herbarium specimens. I am also grateful to Ms. K. Takenaka of the Koishikawa Botanical Garden of Tokyo University for providing
cultivated samples. This study was supported by a Grant-in-Aid for JSPS Fellows 18K14785 to K. H.
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