Hosta polyneuronoides Yahara & Se. Fujii 2023, sp. nov.
Creators: name: Yahara, Tetsukazu
name: Hirota, Shun K.
name: Fujii, Seiko
name: Kokami, Yasushi
name: Fuse, Kengo
name: Sato, Hiroyuki
name: Tagane, Shuichiro
name: Suyama, Yoshihisa
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Asparagales
Asparagaceae
Hosta
Hosta polyneuronoides

description: 2. Hosta polyneuronoides Yahara & Se.Fujii sp. nov.  
Fig. 9  
Diagnosis.  
 Hosta polyneuronoides is distinguished from H. tardiva subsp. densinervia in having 3-10 flowers per inflorescence (in contrast to 15-25 in subsp. Hosta tardiva densinervia) and anthers 3.5-4 mm long (compared to 5 mm long).   
Type.  
 Japan. Kochi Pref.: Agawa-gun, Ino-cho, near Nitaki Bridge, 237 m elev., 20 Aug. 2020, T. Yahara, K. Fuse & H. Sato JPN1378 with flowers (holotype FU!).   
Description.  
Herbs perennial. Leaves basal, spiral, long petiolate, 3-15 per ramet; blades ovate or oblong-ovate, 7.5-28.5 cm long, 3.3-15.3 cm wide, 0.9-2.9 times longer than width, thinly papery, glabrous on both surfaces, base cuneate to subcordate, apex acute to short acuminate, margin entire, veins 8-9 pairs, smooth on the lower surface; petioles 5-40 cm long, narrowly winged, 0.3-0.5 cm wide, glabrous. Scape 15-51 cm long, rachis terete, bract lanceolate, 4 cm long, 0.3-0.5 cm wide, light green, glabrous. Raceme 4.3-9 cm long, 3-10-flowered; flower bracts vivid (not withering) in anthesis, erect or diagonally spreading, whitish green, oblong-lanceolate, boat-shaped, 1.2-3.1 cm long, 0.1-0.8 cm wide, membranous, glabrous, apex acuminate. Flowers not fragrant, 5.7-6.0 cm long; pedicels 0.6-1.3 cm long, glabrous. Perianths white or very pale purple-white, funnel-form, 2.1-4.9 cm long, glabrous, 6-lobed; tube abruptly dilated from apical 2/3, lobes narrowly triangular, 0.7-1.2 cm long, 0.4-1 cm wide, apex acute. Stamens 6, 0.1-0.4 cm exerted from perianth; filaments white, free, 4.5-4.8 cm long, glabrous, anthers purple to yellow when fresh, dark blue-grey to light yellow when dried, 3.5-4 mm long. Ovary ellipsoid, 0.5 cm long, glabrous style 5.5-5.7 cm long, upwardly curved at the distal part, subequal to 1.5 cm exerted from perianth, glabrous, stigma capitate. Capsules or seeds not observed.  
Phenology.  
Flowering from July to August.  
Distribution and habitat.  
 Japan (Kochi and Ehime Prefectures). Hosta polyneuronoides grows on open or shaded rocks and rock cliffs along rivers in the upper reaches and headwaters of the Yoshino River, and on the rocky ridgeline from Mt. Ishizuchi to Mt. Komochi-gongen and its vicinity.   
Etymology.  
This subspecies was named for its resemblance to H. tardiva subsp. densinervia identified as Hosta kikutii var. polyneuron by Fujita (1976).  
Conservation status.  
Using criterion D1 for IUCN Red List categories (IUCN 2012, IUCN 2022), we recommend that this species be classified as NT (Near threatened) because its population is estimated to exceed 1000 but may be declining under the influence of river bank construction and collection for horticulture.  
Japanese name.  
Oku-sudare giboshi (new).  
Additional specimens examined.  
 Japan. Ehime Pref.: Niihama City, Mt. Higashi-akaishi, 970 m elev., 21 Jun. 2021, T. Yahara et al. JPN6269-6271 sterile (FU!); ditto, 1040 m elev., 21 Jun. 2021, T. Yahara et al. JPN6153-6156 sterile (FU!); Mt. Ishizuchi, 28 Jul. 1972, S. Takafuji 799 with flowers (KYO!); Kamiukena-gun, Mt. Ishizuchi, 1600 m elev., 23 Jun. 2021, T. Yahara et al. JPN6390 sterile (FU!); ditto, 1980 m elev., 23 Jun. 2021, T. Yahara et al. JPN6407 sterile (FU!); Saijyo City, Mts. Ishizuchi, from Yoake-toge to Mt. Nishinokanmuri-dake, 1600 m elev., 7 Aug. 1971, H. Takahashi & N. Fujita 226 with flowers (KYO!). Kochi Pref.: Nagaoka-gun, Motoyama-cho, Along Asemi River, 480 m elev., 19 Aug. 2020, T. Yahara et al. JPN1327-1329 with flower buds (FU!); Tosa-gun, Okawa-mura, 570 m elev., 24 Jun. 2021, T. Yahara et al. JPN6493-6495 sterile (FU!); Tosa-gun, Ohkawa-mura, Kawasaki, 400 m elev., 24 Jun. 2021, T. Yahara et al. JPN6501-6503 with flower buds (FU!); Tosa-gun, Ohkawa-mura, Takano, 24 Jun. 2022, K. Fuse et al. JPN12529, 12530, 12532, 12535 sterile (FU!); Tosa-gun, Ohkawa-mura, near Okina Waterfall, 443 m elev., Jul. 25, 2023, Se. Fujii, FJW49-1, 2 with flowers (MBK!); Tosa-gun, Tosa-cho, 24 Jun. 2022, K. Fuse et al. JPN12506 -12508 sterile (FU!); Agawa-gun, Ino-cho, 750 m elevation, 23 Jun. 2021, T. Yahara et al. JPN6449-6451 sterile (FU!); Agawa-gun, Ino-cho, 900 m elevation, 23 Jun. 2021, T. Yahara et al. JPN6446-6448 sterile (FU!); Agawa-gun, Ino-cho, Kamegamori Forest Road, 1650 m elev., 22 Jun. 2021, T. Yahara et al. JPN6342, 6361 sterile (FU!); ditto, Mt. Komochi-gongen, 29 Jun. 2022, K. Fuse et al. JPN12663, 12664 sterile (FU!); Agawa-gun, Ino-cho, Ohmori-gawa dam, 755 m elev., 3 May 2022, Se. Fujii JPN12427 sterile (FU!); Agawa-gun, Ino-cho, Terakawa-Ohdaru, 29 Jun. 2022, K. Fuse et al. JPN12666 -12668 sterile (FU!). The sterile specimens were identified using MIG-seq.   
Note.  
 Two specimens collected from Mt. Ishizuchi (S. Takafuji 799 and H. Takahashi & N. Fujita 226) were cited in the original description of H. shikokiana (Fujita 1976), but were identified as H. polyneuronoides by molecular evidence and also morphologically in having leaves not undulate along the margin and not lustrous below, perianths not purple and without dark purple veins, and anthers 0.4 mm long.
description: Published as part of Yahara, Tetsukazu, Hirota, Shun K., Fujii, Seiko, Kokami, Yasushi, Fuse, Kengo, Sato, Hiroyuki, Tagane, Shuichiro & Suyama, Yoshihisa, 2023, Molecular phylogeny and taxonomy of Hosta (Asparagaceae) on Shikoku Island, Japan, including five new species, one new subspecies, and two new status assignments, pp. 137-187 in PhytoKeys 235 on page 137, DOI: 10.3897/phytokeys.235.99140