Rhododendron sohayakiense Y.Watan. & T.Yukawa, 2019

Yoichi, Watanabe, Minamitani, Tadashi, Oh, Sang-Hun, Nagano, Atsushi J., Abe, Harue & Yukawa, Tomohisa, 2019, New taxa of Rhododendron tschonoskii alliance (Ericaceae) from East Asia, PhytoKeys 134, pp. 97-114 : 97

Rhododendron sohayakiense Y.Watan. & T.Yukawa sp. nov. Figs 1 , 5 , 6

Diagnosis.

This species is similar to Rhododendron tschonoskii Maxim, but is distinguishable through its 4 corolla lobes and its pinnate nerves on the adaxial leaf surface.

Type.

JAPAN. Shikoku: Ehime Pref., Kumakogen Town, Mt. Tsutsujo-yama, 33°44'00.01"N, 133°09'33.40"E, on ridge of the mountain, 1800 m, 20 July 2016 (fl), Y. Watanabe and M. Takahashi Ttj02 (holotype TNS; isotypes TNS, KYO).

Additional specimens examined.

JAPAN. Kii Peninsula, Honshu: Nara Pref., Yoshino County, Kamikitayama Village, Mt. Oodaigahara, Daijyagura, 1500 m, 23 Aug 1956 (fr), G. Murata 10133 (KYO); Nara Pref., Yoshino County, Kamikitayama Village, Mt. Oodaigahara, Daijyagura, 1600 m, 18 Jul 2012 (fl), K. Yamawaki 4869 (KYO); Nara Pref., Yoshino County, Shimokitayama Village, Mt. Kujyaku, 1800 m, 17 Jul 1954 (fl), G. Murata & T. Shimizu 104 (KYO); Shikoku: Tokushima Pref., Miyoshi County, Higashiiya Village, Mt. Tsurugi, 1950 m, 25 Jul 1986 (fl), G. Murata et al. 45946 (KYO); Tokushima Pref., Miyoshi County, Higashiiya Village, Mt. Tsurugi, 1700m, 22 Oct 2012 (fr), Y. Katayama 32 (KYO); Tokushima Pref., Miyoshi County, Nishiiyayama Village, Mt. Nakatsu, 1400 m, 10 Aug 1954, G. Murata 7728 (KYO); Kochi Pref., Nagaoka County, Otoyo Village, Mt. Kajigamori, 1200 m, 22 Aug 1964, G. Murata 18671 (KYO); Ehime Pref., Kamiukena County, Kumakougen Town, Mt. Ishizuchi, between Dogamori and summit, 1600-1980 m, 27 Jul 1983 (fl), G. Murata 44754 (KYO); Ehime Pref., Saijyo City, Mt Ishizuchi, between starting point and summit, 1400-1850 m, 17 Jul 1992 (fl), T. Minamitani 43440 (TNS); Ehime Pref., Niihama City, Mt. Douzanmine, 1300 m, 15 Jul 1980 (fl), K. Tsuchiya 491 (KYO); Ehime Pref., Uma County, Mt. Higashiakaisi and Mt. Futatsudake, 1600 m, 8 Sep 1961 (fr), G. Murata 14993 (KYO); Ehime Pref, Niihama City, Mt. Higashiakaishi, 33°52'31.03"N, 133°22'26.31"E, 1700 m, 15 Jul 2017 (fl), Y. Watanabe Hga03 (TNS).

Description.

Much branched semi-evergreen shrubs 1-1.5 m tall. Branchlets and petioles with dense appressed flattened brownish strigose hairs. Spring leaves scattered or crowded on upper branchlets; petioles 0.5-1 mm long; blade thick chartaceous, oblong, 10-20 mm long (at maximum within each individual), 4-7 mm wide, apex acute and terminating in a gland, base acute, adaxial surface green, abaxial surface pale green, densely strigose on adaxial surface, glabrous or sparsely strigose on abaxial surface without midrib; midrib prominent abaxially; lateral nerves pinnate, 2-3 paired, obscure raised abaxially. Summer leaves oblanceolate, 5-10 mm long, 1-6 mm wide, densely strigose on both surfaces. Flower buds terminal, single, broadly ovoid, acute, ca. 2 mm long, 2 mm wide; scales widely ovate, densely strigose on upper outer surface. Inflorescences umbel-like, 2-4 flowers. Pedicel 2-4 mm long at flowering, densely appressed hirsute. Calyx saucer-shaped, ca. 1.5 mm in diam., densely strigose, shallowly 4-lobed; lobes semiorbiculate, ca. 0.5 mm long. Corolla white, no blotches, openly tubular-funnelform, 8-12 mm long and wide, dissected 1/2 corolla length into 4 lobes; tube 2-3 mm long, ca. 2 mm wide, glabrous outside, pilose on upper inside; lobes elliptic to oblong, rounded, 3-5 mm long, 2-4 mm wide. Stamens 4, subequal, 5-8 mm long, exserted; filaments densely pilose on lower three-quarters; anthers yellow, oblong, ca. 1 mm long. Ovary ovoid, densely soft strigose, ca. 1.5 mm. Style 4-10 mm long, exserted, glabrous. Capsule ovoid, 2-5 mm long, 2-3 mm wide, densely strigose.

Distribution.

JAPAN: Honshu (Kii Peninsula), Shikoku.

Ecology.

The plants inhabit sunny places and grow on mountain ridges and slopes at altitudes over 1000 m above sea level. In such places, there are few trees and established communities of shrubs and dwarf bamboos ( Sasa sp.). Flowering specimens have been collected from July to August; fruiting specimens have been collected from October to November. Bumblebees are frequent visitors to the flowers, suggesting that they are pollinators of the species.

Etymology.

The specific epithet refers to ‘Sohayaki’ a floristic region in Japan that covers Kii Peninsula of Honshu, Shikoku and Kyushu ( Koidzumi 1931), where the new species is distributed.

Figures

Figure 1. Photographs of flowers and leaves for the new taxa described in this study. A, B Rhododendron sohayakiense var. sohayakiense, Mt. Tsutsujo, Ehime Prefecture, Japan C, D Rhododendron sohayakiense var. kiusianum, Mt. Mukousaka, Kumamoto Prefecture, Japan E, F Rhododendron sohayakiense var. koreanum, Mt. Wolbong, Gyeongsangnam-do, South Korea. Photographs by Yoichi Watanabe.

Figure 5. Distribution of the Rhododendron tschonoskii alliance. Circles and squares showed locations of herbarium specimens (KYO, TNS).

Figure 6. Rhododendron sohayakiense var. sohayakiense. A Flower, side view B Stamen C Pistil D Fruit E Abaxial and F adaxial sides of leaf. Scale bars: 1 mm (A-D); 3 mm (E, F). Drawings by Kumi Hamasaki from Y. Watanabe & M. Takahashi Ttj 02 (holotype, TNS).