Research Article |
Corresponding author: Kiyotaka Hori ( khori@makino.or.jp ) Academic editor: Blanca León
© 2020 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.
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
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I describe Athyrium bipinnatum sp. nov. and discuss morphological differences between closely related species. The 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.
Athyrium, Cornopoteris, Japan, new species
Cornopteris Nakai is a small Asian (Himalayas, East and Southeast Asia) genus of terrestrial ferns that used to be recognized by many pteridologists (e.g.,
Regarding its phylogenetic relationships,
Cornopteroid species of the genus Athyrium are mainly distributed in the Himalayas, in East and Southeast Asia. The exact number of species is unknown.
The following is a brief history of the classification of one Athyrium species, namely Athyrium × christensenianum (Koidz.) Seriz., which is partly the focus of the present study. Athyrium × christensenianum was first described by
Recent studies have reported complicated relationships in the A. × christensenianum complex. First,
First, the morphological characteristics of a tetraploid sexual specimen of Athyrium bipinnatum (Hori 2974) and the sexual specimens (Hori 2975, 2976) described by
A. bipinnatum is similar to A. × christensenianum (
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).
Terrestrial, summer green fern. Rhizomes creeping, occasionally 2-branched, stramineous, 8–15 × 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 × 0.3–0.8 cm, sparsely clothed with stramineous to dark brown scales at the base (3–5 × 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 × 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 × 1.5–3 cm; pinnules, alternate on the basal and middle 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 × 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 ultimate segment, exindusiate, rather persistent; spores regular shaped, 64 regular-shaped spores per sporangium, fertile, ovoid, wrinkled, 42–54 μm × 29–35 μm, brown.
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).
Athyrium bipinnatum is named as a new species with bipinnate blades, which distinguish it from A. × christensenianum. This new species could be one of the parents of A. × christensenianum (
Japan. Honshu: Wakayama pref., Ito county, Kouya town, Mt. Kouyasann, Okunoin, alt. 800 m 7 Aug1954, coll. M. Tagawa (NMNH 01529356, image!); loc. cit., ca. 800 m alt., 7 Aug 1954, coll. S.K. (MAK139!); loc. cit., on soil under 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. Y. Higuchi (TNS471359, image!); Nara pref., Tenkawa village, Mt. Gyojagaeridake, 15 Jul 1954, coll. Iwastuki (MAK 26788!); loc. cit., Dorokawa, Mitarai 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. Yokogurayama, 24 May 1956, Iwatsuki 1603 (PE, NMNH, MNHN, images! MAK! TI!); loc. cit., on soil under planted coniferous forest containing C. japonica, alt. 800 m, 30 May 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, l4 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., Takeda city, Kuju town, Mt. Kurodake, alt. 1140, 31 Aug 1997, S. Tsuji TJ-4346 (MAK).
Key to A. bipinnatum and closely related species in Japan
1 | Blades 2-pinnate pinnatifid in the middle section, yellowish green or light green adaxially | 2 |
– | Blades 2-pinnate or 1-pinnate pinnatifid in the middle section, dark green adaxially | 3 |
2 | Blades yellowish green adaxially, pinnule in the middle section of blade deeply serrated on margin, spores regular | A. crenulatoserrulatum |
– | Blades light green adaxially, pinnule in the middle section of blade shallowly serrated on margin, spores abortive | A. × christensenianum |
3 | Blades 2-pinnate, pinnae straight, sori often single | A. bipinnatum |
– | Blades 1-pinnate pinnatifid, pinnae curved to the apex, sori often lobed | A. decurrentialatum |
Athyrium bipinnatum is known from the western part of Honshu, Shikoku, and Kyushu in Japan (Fig.
IUCN Red List Category. Based on estimates from GeoCAT, the EOO of A. bipinnatum was 53,068 km2; 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. bipinnatum is 44 km2. Based on the IUCN criteria (
Athyrium × christensenianum was first described by
Athyrium bipinnatum is of hybrid origin between a diploid sexual A. crenulatoserrulatum and an extinct or undetected diploid sexual A. decurrentialatum, and it is one of the parents of A. × christensenianum (
Characters | A. bipinnatum | A. × christensenianum | A. crenulatoserrulatum | A. decurrentialatum |
Stipe length (cm) | 7–20 | 25–40 | 20–30 | 20–30 |
Pinna size (cm) | 6–16× 1.5–3 | 15–30 × 5–9 | 10–20 × 5–8 | 8–15 × 3–5 |
Pinna stalk length (cm) | 0.2–0.4 | 0.2–0.4 | 0.4–0.9 | 0–0.2 |
Blade size (cm) | 15–40 × 14–20 | 30–60 × 25–40 | 30–35 × 25–30 | 20–35 × 15–25 |
Blade color adaxially | dark green | light green | yellowish green | dark green |
Blade division medially | 2-pinnate | 2-pinnate pinnatifid | 2-pinnate pinnatifid | 1-pinnate pinnatifid |
Pinnule division medially | shallowly serrated | deeply to shallowly serrated | deeply serrated | shallowly serrated or entire |
Sori | single | sometimes lobed | single | often lobed |
Spore shape | regular | irregular | regular | regular |
Spore size (μm) | 42–54 × 29–35 | 30–44 × 22–39 | 25–37 × 16–20 | 27–45 × 21–35 |
Contrary to the findings of the present study,
In summary, the previously unclear taxonomy of A. × christensenianum was clarified in the present study by describing tetraploid sexual “A. × 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.
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 (TI) 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.