Diplazium x tsukushiense K.Hori & H.Kanemitsu, 2021

Hori, Kiyotaka & Kanemitsu, Hironobu, 2021, Two new hybrids of the genus Diplazium (Athyriaceae) from Japan, PhytoKeys 172, pp. 39-55 : 39

Diplazium x tsukushiense K.Hori & H.Kanemitsu hyb. nov. Figure 4

Diagnosis.

D. x tsukushiense is likened to D. fauriei with fronds 1-pinnate at the apex. However, lower pinnae of D. fauriei are not lobed, finely serrated on the margin. In contrast, lower pinnae of D. x tsukushiense are lobed deeply and 1-pinnate pinnatifid.

Type.

Japan. Kyushu: Fukuoka Prefecture, Nakagawa City, Ooaza-Gokayama, Tsukushiyabakei, 33°26'22.87"N, 130°25'36.76"E, alt. 266 m, planted coniferous forest containing Cryptomeria japonica (Thunb. ex L.f.) D.Don, on soil, 4 Jul 2020, H. Kanemitsu 3755 (holotype: KAG 151590),

Description.

Terrestrial semi-evergreen fern. Rhizomes: creeping, occasionally two-branched, black, 7-30 cm × 0.8-1.3 cm in diam., closely set with roots and persistent, densely clothed with old stipe bases, glabrous; fronds: 2-5 per rhizome; stipes: purplish-green, 20-30 cm × 0.2-0.3 cm in diam., glabrous in the middle to upper sections, sparsely clothed with dark brown scales (3.0-6.0 mm × 1.0-1.5 mm, with small projection on margin) on basal sections, lanceolate; blades: dark green on adaxial surface, 1-pinnate at the apex, 1-pinnate pinnatifid at the base and middle, 30.0-43.5 cm × 20.0-26.0 cm, narrowly ovate; rachises: purplish-green, glabrous; pinnae: 10-15 pairs, ascending, straight, lanceolate, alternate, petiolated (2-11 mm long), serrate to lobed, acute at the apex, sessile near the apex of blades, widely spaced, lowest pair of pinnae slightly reduced, second lowest pair usually largest, 10-16 cm × 2.0-5.0 cm; pinnules: alternate, 10-15 pairs on the basal sections of the blade, reduced distally, ovate to lanceolate, entirely to shallowly serrated, acute at apex in basal part of blade, rather acute at apex in middle part of blade, vein-free, single or double, close to or reaching to the margin, 5-7 pairs in the middle lobe; the most basiscopic pinnules on the lowest pinnae: occasionally absent, slightly short, rather independent from the costa, 3-7 mm × 3-4 mm; sori: long linear- or J-shaped, 1.0-5.0 mm long on the middle of veinlets, 4-10 pairs per ultimate segment, persistent; indusia: cloudy white or brown, same shape as sori, entire, persistent; spores: absent or irregular-shaped, abortive.

Etymology.

The name derives from Tsukushiyabakei, Ooaza-Gokayama, Nakagawa City, Fukuoka Prefecture, west Japan, where Diplazium x tsukushiense was initially found.

Specimens examined.

Japan. Kyushu: Fukuoka Prefecture, Nakagawa City, Ooaza-Gokayama, Tsukushiyabakei, 33°26'22.87"N, 130°25'36.76"E, alt. 266 m, planted coniferous forest containing Cryptomeria japonica (Thunb. ex L.f.) D.Don, on soil, 4 Jul 2020, H. Kanemitsu 3756, H. Kanemitsu 3757, loc.cit., 16 Jul 2018, H. Kanemitsu 2930 (TNS1307651), loc.cit., 12 Dec 1976, S. Tsutsui 13341-3 (TNS341595), loc.cit., 8 Jul 1978, S. Tsutsui 15807 (TNS424776), loc.cit., 6 Nov 1999, Y. Inoue Y-37 (TNS1159163), loc.cit., 11 Aug 1986, coll. by T. Yamanaka (TNS1135951), loc.cit., 11 Aug 1986, coll. by T. Yamanaka (TNS1135952), loc.cit., 11 Aug 1986, coll. by T. Yamanaka (TNS1135953), loc.cit., 11 Aug 1986, coll. by T. Yamanaka (TNS1135954).

Distribution and ecology.

D. x tsukushiense has been determined to be from Kyushu, western Japan (Figures 4 , 5 ). Observed to grow on soil under coniferous forest containing Cryptomeria japonica (Thunb. ex L.f.) D.Don near streams. This hybrid is endemic to Japan. In the type locality, the population is only approximately 10 individuals. Parents D. chinense and D. fauriei are observed in the same locality.

Conservation status.

IUCN Red List Category. Based on estimates from GeoCAT, the EOO of D. x tsukushiense is 0.001 km2. The known AOO of D. x tsukushiense is 4.0 km2. Only 10 individuals are found in the type locality and population size is decreasing because of illegal waste dumping in forests. Therefore, this hybrid should be considered critically endangered (CR), as per the IUCN (2012) criteria. A formal evaluation of endangerment is summarised by the following IUCN hierarchical alphanumeric coding: CR B1ab (i, iv, v)+B2ab (i, iv,v)+C1+C2 a (i, ii) b+D.

Figures

Figure 4. Diplazium x tsukushiense K. Hori & H. Kanemitsu A lower stipe scale B habit C detail of abaxial pinnule A-C from the holotype (KAG 151590) (illustration by K. Hori).

Figure 5. Map showing the known distribution in Japan of D. x kanayamaense = Red circle and D. x tsukushiense = Blue circle.