Hosta tosana F. Maek., J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 5: 376. 1940.

9. Hosta tosana F. Maek., J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 5: 376. 1940.

Fig. 21, 22, 23, 24

Hosta tosana F. Maek., J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 5: 376. 1940. Type. Japan, Shikoku: Kochi Prefecture, Mt. Kajigamine (now called Kajigamori), T. Yoshinaga s.n. (unknown; not deposited in TI).

Hosta kikutii var. tosana (F. Maek.) F. Maek., Engei-daijiten 2:633. 1950; Tamura & Fujita in Iwatsuki et al. Fl. Jap. IVb: 143. 2016.

Hosta tosana var. caput-avis F. Maek., J. Jap. Bot. 22: 64. 1948. Type. JAPAN. Kochi Pref., Yanase, K. Yasui 332 (unknown; not deposited in TI).

Hosta caput-avis (F. Maek.) F. Maek. in Nakai, Iconogr. Pl. Asiae Orient. 5: 495. 1952.

Hosta kikutii var. caput-avis (F. Maek.) F. Maek., Engei-daijiten (Encycl. Hort.) 2: 633. 1950; Fujita, Acta Phytotax. Geobot. 27: 79. 1976.

Phenology.

Flowering in June to July.

Distribution and habitat.

Japan (Kochi and Tokushima Prefectures). This species grows on wet slopes, rocky cliffs, rocky riverbanks, and tree trunks in the elevations from 77 m to 1420 m.

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 deer browsing, river bank construction, and collection for horticulture.

Japanese name.

Tosa-no-giboshi (Maekawa 1940), Unazuki-giboshi (Maekawa 1948).

Specimens examined.

Morphs corresponding to "var. Hosta tosana tosana ":

Kochi Pref.: Locality not specified, cultivated in Tokyo, 1 Aug. 1943, Maekawa 7043 with flowers (TI; the cultivated plant may have been collected by T. Yoshinaga from the type locality, as this is the only specimen of this taxon deposited in TI, where Maekawa studied Hosta); Nagaoka-gun, Otoyo-cho, Mt. Kajigamori, 30 Apr. 2022, Se. Fujii JPN12424 sterile (FU!); Kami City, Monobe Town, O-dochi, 500 m elev., 25 Jun. 2021, T. Yahara et al. JPN6619-6620 with flowers (FU!); ditto, Go-o-do, 553 m elev., cultivated at Makino Botanical Garden, 8 Apr. 2021, T. Yahara & Se. Fujii JPN3931-3933 sterile (FU!); ditto, 600 m elev., 25 Jun. 2021, T. Yahara et al. JPN6614 & 6616 with flowers, JPN6611-6613, 6615 sterile (FU!); Miyanose, 400 m elev., T. Yahara et al. JPN6603 sterile (FU!); Befu, 550 m elev., cultivated at Makino Botanical Garden, 8 Apr. 2021, T. Yahara & Se. Fujii JPN3934 sterile (FU!); Befu Valley, 700 m elev., 25 Jun. 2021, T. Yahara et al. JPN6553-6555 with flowers (FU!); Aki City, 77 m elev., cultivated at Makino Botanical Garden, 8 Apr. 2021, T. Yahara & Se. Fujii JPN3935 sterile (FU!); Aki-gun, Kitagawa-mura, Shima, along the Nahari River, 28 May 2022, K. Fuse et al. JPN12653 sterile (FU!). Tokushima Pref.: Mt. Tsurugi, 14 Aug. 1931, Z. Tashiro s.n. with flowers (KYO!); ditto, below Minokoshi, 1400 m elev., 14 Aug. 1954, G. Murata 7977 with flowers (KYO!); ditto, 1420 m elev., 23 Jun. 2022, T. Yahara et al. JPN12821 -12823 sterile (FU!); Higashiiyayama-mura, Inter Sugeoi et Minokoshi, 800 m elev., 12 Aug. 1954, G. Murata 7814 & 7816 with flowers and young fruits (KYO!); Naka County, Wajiki Town, 14 Jul. 1965, S. Takafuji 216 with flowers (KYO!); ditto, Kizawa Village, 24 Jul. 1980, S. Takafuji 1442 with flowers (KYO!); ditto, Riu-toge in Miyahama-mura, 2 Jul. 1952, G. Murata 5752 with flowers (KYO!); ditto, Kizu Village, 24 Jul. 1974, S. Takafuji 950 with flowers (KYO!).

Morphs corresponding to "var. Hosta tosana caput-avis ":

Kochi Pref.: Aki-gun, Yanase, 25 Jun. 2020, K. Fuse et al. 12536-12539 sterile (FU!); Kami City, Monobe Town, Befu Valley, 25 Jun. 2021, T. Yahara et al. JPN6524-6526 with flower buds, 6571 with flowers, 6572 with flower buds (FU!); Mt. Ishidate, 25 Jun. 2021, T. Yahara et al. JPN6585-6587, 6593-6596 with flower buds (FU!); on the river bank of Yanase, 1000 m elev., 20 Jul. 1958, S. Hatusima 22009A with wilted flowers (KAG056576!); transplanted from Yanase, 29 Jun. 1960, S. Hatusima s.n. with flowers (KAG056577!); ditto, 10 Jun. 1967, Hatusima s.n. with flowers (KAG056578!).

The Kagami River lineage:

Kochi Pref.: Kochi City, Tosayama, Hirose, 85 m elev., 3 Oct. 2008, Hamaguchi & N. Shintani PRC-00118 with fruits (MBK0208327!); ditto, 14 Jul. 2001, K. Hosokawa et al. FOK-001722 with flowers (MBK0104375!); Kuwao, 130 m elev., 14 Jul. 2013, A. Sakamoto FOS-004959 with flowers (MBK0247214!, MBK0247215!); from Kuwao to Tsuami, 27 Jul. 1968, N. Naruhashi & M.Wakabayashi 223 with flowers (KYO!); Namekawa, 30 m elev., 19 Aug. 2020, T. Yahara et al. JPN1265 with fruit, JPN1266 sterile, JPN1267 sterile, JPN1269 with fruit (FU!); Kajitani, 160 m elev., 29 July 2013, A. Sakamoto FOS-005031 with young fruits (MBK0247386!) and FOS-005032 with young fruits (MBK0247387!); Miyanokubo, 160 m elev., 14 Jul. 2013, A. Sakamoto FOS-004958 with flowers (MBK0247213!); ditto, 170 m elev., 14 Jul. 2013, A. Sakamoto FOS-004957 with fruits (MBK0247212!); Oh-ana Valley, 110 m elev., 19 Aug. 2020, T. Yahara et al. JPN1298 sterile, JPN1299 sterile, JPN1307 with flowers (FU!); Kagami-mura, Kawaguchi, along the Kagami River, 9 Jul. 1958, T. Yamanaka 25548 with flowers (KYO!).

Note.

The Kagami River lineage is sister to a clade comprising all other samples (Fig. 5). It is morphologically distinguished from other samples by having leaves with fewer lateral veins (5-11 compared to 10-13) that run at wider intervals (1 cm vs 0.7 cm), and it is distinct in its occurrence at elevations below 300 m (compared to elevations ranging from 77 m to 1420 m, usually above 300 m). It is likely that this lineage could be classified as a subspecies of H. tosana or a separate species. However, further studies are necessary to arrive at definitive conclusions regarding this lineage because H. tosana is a polymorphic species widely distributed in the eastern part of Shikoku. Nonetheless, our collections did not cover the entire range of this species.

According to the MIG-seq tree, two genetically distinct lineages are distributed along the Monobe River in Kami City (Figs 5, 6). The lineages were identified as H. tosana var. tosana and H. tosana var. caput-avis. However, population genetic evidence shows that the two varieties hybridize in the sympatric population along the Befu Valley. The available evidence indicates that var. Hosta tosana caput-avis is difficult to distinguish from var. Hosta tosana tosana in Kami City.

While the two varieties appeared to lack distinction in Kami City, the population of Yanase, which serves as the type locality for H. tosana var. caput-avis, exhibited clear differentiation from the populations in Kami City. However, just like in the case of the Kagami River lineage, further studies using a larger sample size are necessary to definitively conclude about the Yanase lineage.

A lineage distributed in SE Kinki, Honshu (H. sp. 4 in Fig. 1) was identified as H. kikutii var. caput-avis by Fujita (1976) and Fujita and Tamura (2008), and later treated as H. kikutii var. tosana by Tamura and Fujita (2016). However, it is not related to H. tosana of Clade 4, but to H. longipes of Clade 6 (Fig. 1).