Struthiopteris castanea (Makino & Nemoto) Nakai, 1933

Molino, Sonia, Santos, Guillermo, Vázquez, Rubén, Medina, Rafael & Gabriel, José María, 2024, Monograph of the genera Struthiopteris Scop. and Spicantopsis Nakai (Blechnaceae, Polypodiopsida), Phytotaxa 677 (1), pp. 1-48 : 23-24

Struthiopteris castanea (Makino & Nemoto) Nakai ( Figure 9D ; Figure 14A‒B ; Figure 15 ).

Type:— JAPAN. Prov. Rikuzen, Mt. Kurikoma-yama, 25 August 1890, no collector s.n. ( TNS 19854! photo, lectotype, designated in

Makino & Nemoto 1925). Synonyms:— ≡ Blechnum castaneum Makino & Nemoto. = Struthiopteris castanea (Makino & Nemoto) Nakai var. viridipes Honda (1937: 644) . Type:— JAPAN. Honsyu, Oze, Prov. Iwasiro, 1935,

T. Sakai 1904 ( TI not seen, holotype) ; ≡ Struthiopteris castanea (Makino & Nemoto) Nakai f. viridipes (Honda) Tagawa (1959:

143). Invalid designation: Lomaria castanea Makino (1891: 45) . nom. nud.

Plants terrestrial; rhizomes short, ascending, with brownish scales, linear lanceolate, 0.5‒1.5 x 3‒8 mm, with the central zone narrowly sclerotized from base to apex, dark brown, entire margins lighter brown; fronds dimorphic, sterile fronds (13) 25 (41) cm, shortly petiolate, stipes dark brown, brown, black or purplish, 0.5‒3 (10) cm, laminae narrowly lanceolate, 3‒6 x 10‒40 cm, 1-pinnate or pinnatisect, apex conform, with uniseriate multicellular hairs topped by a red gland of variable size on both sides of the lamina, rachises dark brown basally, light brown or green towards apex, grooved adaxially, pinnae entire, tapering towards the base, the middle ones 0.3‒0.8 x 1‒3 cm, rounded and mucronate at apex, costae grooved adaxially, prominent abaxially; veins free, simple to 1-furcate, ending in adaxial submarginal hydathodes, stomata aligned following veins on abaxial face of pinnae; fertile fronds up to twice as long as sterile fronds, stipes brown, black or purplish, red during growth, 7‒12 (20) cm, laminae narrowly lanceolate, 2.7‒5.2 x 16‒44 cm, 1-pinnate or pinnatisect, with uniseriate multicellular hairs topped by a red gland of variable size on both sides of the lamina, pinnae contracted, the middle ones 0.1‒0.3 x 1‒3 cm,; sori linear, continuous, forming coenosori on both sides of costa, covering entire length of pinna, decurrent towards rachis; indusia linear, continuous; sporangia with 16‒20 arc cells; spores monolete, 40‒50 x 50‒65 µm, perisporium irregularly folded.

Habitat and distribution:— Endemic to Japan. Occurs from the Tohoku region to the northern tip of Kanto, from Shin-etsu northward, and in San-in from northern Hiroshima Prefecture ( Figure 4 ) ( Iwatsuki 1992). Grows in masses in hillside undergrowth in the subalpine zone of Japan. Up to 1,100 m ( Ohwi 1953, Iwatsuki 1992, Iwatsuki et al. 1995).

Chromosome number:— 2 n = 340, decaploid ( Fabbri 1965, Nakato 1987).

Etymology:— The epithet is used to designate chestnut-like colour of the axes ( Stearn 1973).

Vernacular name:— Miyama-shishigashira (ミヤマシシガシラ, Japanese) ( Iwatsuki 1992). The Japanese name means “lion’s head of Miyama”. Lion’s head (shishigashira) is the name usually given to Spicantopsis niponica , presumably because of the similarity of its scales to the mane of a lion. The scales of Struthiopteris castanea do not show this effect, but the plant in general resembles S. niponica , so we assume that, as it was described later, it was assigned this vernacular because of its similarity to that species. We do not know why it is associated with Miyama, as the original material is not from Miyama.

Taxonomic notes:— This species resembles the representatives of the genus Spicantopsis present in Japan but can be easily distinguished by the colour of the stipe, very dark in S. castanea and green or very light brown in Spicantopsis species. Although it does not cohabit with its congeners, it is actually very similar to Struthiopteris spicant , from which it can be distinguished by the ornamentation of the stipe, very densely punctate in S. castanea and striate or only slightly punctate in S. spicant .

It is common to find specimens of Lomaridium contiguum ( Mettenius 1861: 70) Gasper & V.A.O. Dittrich in Gasper et al. (2016: 212) labelled under the name Blechnum castaneum Copeland (1929: 361) , as this was an illegitimate name given to this species by Copeland (1929) but was already applied earlier to the present Struthiopteris castanea .

The name Lomaria castanea Makino has been used as a basionym for Struthiopteris castanea on numerous occasions ( Ohwi 1953, Tagawa 1959, Nakaike 1975, 1982), but that this is a name that was not validly published as it did not present a description alongside the name ( Makino 1892), as has been noted in Molino et al (2019b). In fact, Makino’s next mention of the species is to synonymize it with Struthiopteris spicant (sub. Blechnum spicant, Makino 1899 ). A publication by Nakaike (1983) that was overlooked in Molino et al. (2019b) confirms this view. It states that, as already indicated by Christensen (1934), the name Blechnum castaneum was first correctly published by Makino & Nemoto (1925) with a short description in Japanese. This is confirmed by the finding of the type by Nakaike (1983) in the TNS herbarium, with Nemoto’s handwriting specifying the name Blechnum castaneum (TNS19854! photo).

At Oze (National Park in Fukushima, Niigata, and Gunma prefectures, north of Tokyo) a form with green costa, stipe and rachis has been collected and named Struthiopteris castanea var. virividipes , but it is not a taxon recognized by some authors ( Iwatsuki 1992), and we have not found any individuals with these characteristics. The axes of Spicantopsis niponica are clearer than in S. castanea , and this plant shows a lot of variation (see section on this species), so maybe that collection was a rare specimen of this species.

Its chromosomal number, 2 n = 340 (decaploid), is remarkable, being the highest number known for the Blechnaceae family. It is not yet known if this high chromosome number responds to some kind of adaptation, although it is known that this species occupies areas of high altitude, so it could be related to its ability to live in this more hostile territory ( Nakato 1987). This chromosomal difference would be expected to be observed in spore size, but the spores of S. castanea have been shown to be only slightly larger than those of its tetraploid relatives, S. fallax and S. spicant ( Molino et al. 2020) .

Additional specimens examined:— JAPAN. Honshu. Pref. Akita: 1927, Makino 32953 ( S1980 !) . Pref. Aomori: Hakkōda , 1861, Maximowicz s.n. ( S2145 !) ; Hakkōda, Iwakura , 5 September 1959, K. Iwatsuki 5049 ( S1971 !; U0043510 ! photo; US 2356861!) ; Shichinohe-machi , 31 August 1980, E. Fukushi 8422 ( TNS732190 !) ; Ibidem, no collector ( TNS739308 !). Pref. Fukui: Imadate-gun , Ikeda-cho , Hekosan , 14 August 1992, T. Kawahara s.n. ( TNS792167 !) ; Imadate-gun, Ikeda-cho, Kanmuri-yama , no date, Y. Saito s.n. ( TNS792168 !). Pref. Fukushima: Hinoemata-mura , 22 July 1934, S. Okuyama 410 ( TNS45261 !) ; Minamiaidu-Gun, Hinoemata-Mura, prope Sanzyono-taki , 12 August 1935, J. Ohwi s.n. ( MICH1613813 ! photo). Pref. Iwate: Isawa-cho , 1 August 1968, no collector ( TNS426905 !) ; Shizukuishi-cho , 28 September 1980, no collector ( TNS739310 !) ; Wakayanagi-mura , 29 August 1951, N. Karizumi s.n. ( TNS115371 !). Pref. Gifu: Ohno-gun, Shirakawa-mura, Sanpoiw adake, 15 August 1992, M. Murase 5453 ( TNS792169 !). Pref. Gunma: Minakami-mura, 23 August 1894, K. Watanabe 310 ( TNS63209 !) ; Tone-gun, Minakami-chō, Tanigawa Mt. , Tenjindaira , Kuma-ana sawa hinangoya, 6 June 2011, A. Ebihara et al.2782 ( TNS108194 !) ; Yamanohana-Hatomachi pass, Katashina-mura Tone-gun , 17August 1974, K. Suzuki s.n. ( MO249980 !). Pref. Hyogo: Mikana-gun, Onsen-cho, Ueyama-kogen, 25 July 1999, T. Kobayashi s.n. ( TNS700642 !). Pref. Miyagi: 5 September 1966, H. Koyama & F. Konta 1943 ( TNS924264 ! photo). Pref. Nagano: Otari-mura, 26 July 1979, J. Haginiwa 29502 ( TNS979502 ! photo) ; Otari-mura , 14 September 1985, M. Futoshi 81107 ( TNS832504 !) ; Otari-mura , 27 July 1979, J. Haginiwa s.n. ( TNS979503 !) ; Shinano, Shumominochi-gun, Minochi-mura , 28 June 1956, M. Mizushima 13853 ( S1982 !). Pref. Niigata: Ivihirose , 18 August 1949, Y. Ikegami 13386 ( MO5423252 !) ; Koide-machi , 26 August 1967, Konta 6405 ( TNS924267 !; TNS924268 !) ; Shibata-shi , 24 October 1963, F. Konta 3344 ( TNS924269 ! photo) ; Ibidem , 24 December 1963, F. Konta 3340 ( TNS924263 !) ; Ibidem , no date, F. Konta 3350 ( TNS924265 ! photo; TNS924266 ! photo) ; Yamato-machi , 8 August 1964, Y. Ikegami s.n. ( TNS184551 !) ; Yamato-mura, 17 July 1954, S. Iwano s.n. ( TNS110853 !). Pref. Toyama: Yatsuo-machi , 15 August 1955, A. Kirino s.n. ( TNS280676 !) ; Yamagata, Iide-machi , 18 August 1966, D. Shimizu s.n. ( TNS172556 !) ; Ibidem ( TNS172559 !) .

Figures

FIGURE 4. Distribution of Struthiopteris castanea extracted from GBIF.

FIGURE 9. Spores of Spicantopsis: A. S. amabilis (J. Faurié, 5612 P01406648). B. S. hancockii (R. Knapp 4311, P02435597). C. S. niponica var. niponica (M. Tagawa & K. Iwatsuki 3014, P01575937). Spores of Struthiopteris: D. S. castanea (Y. Saito s.n., TNS792168). E. S. fallax (P. Wasowicz & J.M. Gabriel y Galán s.n., MACB 109359); F. S. spicant var. spicant (A. Santos s.n., MACB36152). G. S. spicant var. homophyllum (Barrera s.n., MACB32367); H. S. spicant var. pradae (S. Molino et al s.n., MACB110654). Bar = 30 μm in A–D; 22 μm in E–H.

FIGURE 14. Struthiopteris species in the field. A-B. Struthiopteris castanea. A. Habit; B. Detail of the abaxial side of the fertile frond, bearing sori; C-D. Struthiopteris fallax. C. Habit; D. Detail of the abaxial side of the fertile frond, bearing sori; E-F. Struthiopteris spicant var. spicant. E. Habit; F. Detail of the adaxial side of the fertile frond; G. Struthiopteris spicant var. homophyllum, detail of the abaxial side of the fertile frond, bearing sori; H. Struthiopteris spicant var. pradae, detail of the abaxial side of the fertile frond, bearing sori. Pictures: A & B. Shirakawa, Gifu, Japan, by Hiroki Moriwaki; E & H. Zamora, Castilla y León, Spain, by Sonia Molino; F. Soria, Castilla y León, Spain, by Sonia Molino; G. La Coruña, Galicia, Spain, by Sonia Molino.

FIGURE 15. Illustration of Struthiopteris castanea.A. Habit (no collector, TNS739310); B. Sporangium (M. Mizushima 13,853, S1982); C. Rhizome scale (T. Kawahara s.n., TNS792167). Scale: 4 cm in A; 100 µm in B; 1 mm in C.