Athyrium bipinnatum K.Hori, 2020

Hori, Kiyotaka, 2020, Athyrium bipinnatum K. Hori (Athyriaceae), a new cornopteroid fern from Japan, PhytoKeys 148, pp. 93-104 : 93

Athyrium bipinnatum K.Hori sp. nov. 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. However, A. bipinnatum has more short stipes (10-20 cm long), smaller blades (20-40 cm × 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 × 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 × 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.

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. 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

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.

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 ( IUCN 2001, 2012), A. bipinnatum falls into the Endangered (EN) category. A formal evaluation of endangerment can be summarized by the following IUCN hierarchical alphanumeric coding system of criteria and subcriteria: EN A1abc+A2+C1+C2a(i).

Figures

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 (MAK 466762) (illustration by K. Hori).

Figure 5. Map showing the known distribution of Athyrium bipinnatum in Japan.