Hosta takiminazukiflora subsp. grandis Se.Fujii & Yahara, 2023

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, PhytoKeys 235, pp. 137-187 : 137

6 А. Hosta takiminazukiflora subsp. grandis Se.Fujii & Yahara subsp. nov.

Fig. 16

Diagnosis.

Hosta takiminazukiflora subsp. grandis is distinguished from subsp. Hosta takiminazukiflora takiminazukiflora in having scapes 31-36 cm long (compared to 8.6-28.5 cm long in subsp. Hosta takiminazukiflora takiminazukiflora ), broader leaf blades (13-14 cm wide compared to 3.6-10.5 cm wide), cordate leaf base (vs. cuneate to obtuse), glaucous lower leaf surface, lateral veins 12-13 pairs (as opposed to 6-10 pairs), and petioles green, not dotted with purple.

Type.

Japan. Kochi Pref.: Tosa-gun, Tosa-cho, along Seto River , 24 Jun. 2021, T. Yahara et al. JPN6487 with flowers (holotype FU!) .

Description.

Herbs perennial. Leaves basal, spiral, long petiolate, 3-5 per ramet; blades oblong-ovate, 22-25 cm long, 13-14 cm wide, 1.7-1.8 times longer than width, thinly papery, glabrous on both surfaces, base usually cordate, often decurrent, apex acuminate, margin entire, veins in 12-13 pairs, smooth or slightly papillose on the lower surface; petioles 35-38 cm long, narrowly winged, wing 0.3 cm wide, glabrous. Scape 31-36 cm long, terete. Raceme 12-15.5 cm long, 4-18-flowered; flower bracts vivid (not withering) in anthesis, erect, purplish light green, oblong-lanceolate, boat-shaped, 2.8-4.3 cm long, 0.4-0.5 cm wide, papery, glabrous, apex acuminate. Flowers not fragrant; pedicels 1.9-2 cm long, pale purple, glabrous; perianths 3.8-4.9 cm long, funnel-form, glabrous, 6-lobed, pale blue-purple outside, almost white to pale purple inside, midveins faintly purplish adaxially; tube dilated from apical 2/3, lobes oblong-triangular, 1.2-1.3 cm long, 0.7-0.8 cm wide, apex acute. Stamens 6, ca. 0.5 cm exerted from perianth; filaments 4.3-4.5 cm long, upwardly curved at the distal part, white, free, glabrous, anthers purple when fresh, dark blue-grey when dried, 3 mm long. Ovary ellipsoid, 0.6-0.7 cm long, style 4.5-5.1 cm long, upwardly curved at the distal part, ca. 1 cm exerted from perianth, glabrous, stigma capitate. Capsules or seeds not observed.

Phenology.

Flowering in late June.

Distribution and habitat.

Japan (Kochi Prefecture) (endemic). This species grows on soil near waterfalls, whereas subsp. Hosta takiminazukiflora takiminazukiflora grows on rock cliffs.

Etymology.

The specific epithet is derived from its larger plant size rather than that of the typical subspecies.

Conservation status.

Using criterion D1 for IUCN Red List categories ( IUCN 2012, IUCN 2022), we recommend that this species be classified as CR (Critically endangered) because its population is estimated to be fewer than 50.

Japanese name.

Setogawa-giboshi (new).

Additional specimens examined.

Japan. Kochi Pref.: Tosa-gun, Tosa-cho, along Seto River , 24 Jun. 2021, T. Yahara et al. JPN6488 - 6489 with flowers (FU!); ditto, 24 Jun. 2022, K. Fuse et al. JPN12518 - 12521 with flowers (FU!) .

Note.

In the type locality, subsp. Hosta takiminazukiflora grandis grows side by side with subsp. Hosta takiminazukiflora takiminazukiflora , and both subspecies flower simultaneously in late June, but the two subspecies are morphologically distinct and subsp. Hosta takiminazukiflora grandis formed a monophyletic group significantly separated from the sympatric population of subsp. Hosta takiminazukiflora takiminazukiflora . Therefore, subsp. Hosta takiminazukiflora grandis appears to be an evolutionary distinct lineage. This lineage is of particular interest as a research material for studying rapid speciation under disruptive selection and also serves as a valuable resource for breeding Hosta cultivars. Taking into account these characteristics, as well as its morphological distinctiveness, we distinguish it as a subspecies. Due to its limited population size, conservation measures are urgently necessary.

Figures

Figure 16. A, B flowering plant of H. takiminazukiflora subsp. grandis (JPN 6487, 24 Jun. 2021) C its lower leaf surface. Scale bars: 10 cm (A); 1 cm (B).