A New Species, Cerasus Kumanoensis from the Southern Kii Peninsula, Japan

ISSN 1346-7565 Acta Phytotax. Geobot. 69 (2): 119–133 (2018) doi: 10.18942/apg.201801

A New Species, Cerasus kumanoensis from the Southern Kii Peninsula, Japan

Toshio Katsuki

Tama Forest Science Garden, Forestry and Forest Products Research Institute, Todori 1833-81, Hachioji, Tokyo 193-0842, Japan. [email protected]

A new species, Cerasus kumanoensis T. Katsuki (Rosaceae), sp. nov., is described from the southern Kii Peninsula, Japan. It is similar to C. jamasakura var. jamasakura and C. leveilleana because the corymbose inflorescences and extended peduncle are identical in these three taxa. However, C. kumanoensis is distinguished by several morphological and phenological characteristics, an earlier flowering period, narrowly ovate and smaller leaf blade (4–8 cm long, 1.8–3.6 cm wide) and glabrous petiole and pedicel.

Key words: Cerasus kumanoensis, flowering cherry, flowering period, Japan, Kii Peninsula

The cherry genus Cerasus Mill. (Rosaceae) is distinct, exhibit genetic differences (Kato et al. widely distributed in the northern hemisphere. 2014), and are treated as independent species in Nine species of Cerasus are native to Japan (Ka- Japan (e.g., Ohwi 1953, Ohba 2001, Ikeda et al. wasaki 1993, Ohba 2001, Ikeda et al. 2017), where 2017), although they have also been treated as va- it has been cultivated for centuries for the aes- rieties or forms of C. serrulata (Lindl.) G. Don ex thetic qualities of its blossoms and where many Loudon (Koehne 1912, Wilson 1916, Chang et al. ornamental cultivars have been reported. Inter- 2007). These three species are characterized by specific hybridization occurs relatively easily and corymbose inflorescences with a long peduncle. numerous hybrid taxa have also been published Cerasus kumanoensis is considered to be close to in Japan. Although Japanese interest in cultivated the three species, because of its corymbose inflo- Cerasus is so high that many studies have re- rescences and a peduncle that often extends to vealed morphological diversity in cultivars and more than 10 mm in length during flowering. hybrids (Wilson 1916, Ohwi 1953, Kawasaki Among the species of Cerasus native to Japan, 1993), in wild trees such interest has been rela- these characteristics occur only within these spe- tively low and the morphological diversity within cies. wild populations has not received much detailed Cerasus kumanoensis has pink petals and a examination. If Japanese wild Cerasus popula- short peduncle (1–4 mm long) during early tions are examined in detail, undescribed taxa blooming. It is similar to C. sargentii var. sargen- may be found, as is the case of C. sargentii (Re- tii in appearance (Fig. 1B–E). The leaf blade on hder) H. Ohba var. akimotoi H. Ohba & Mas. short shoots of C. kumanoensis (4–8 cm long, Saito (Ohba & Saito 2000). Here, I describe a new 1.8–3.6 cm wide) is obviously shorter and nar- species of wild cherry, C. kumanoensis, sp. nov., rower than in C. jamasakura (5–9 cm long, 3–4 from the Kii Peninsula, Japan. cm wide according to Kawasaki 1993), C. leveil- Cerasus jamasakura (Siebold ex Koidz.) H. leana (6–12 cm long, 3–6 cm wide according to Ohba, C. leveilleana (Koehne) H. Ohba and C. Kawasaki 1993) and C. sargentii (7–11 cm long, speciosa (Koidz.) H. Ohba are morphologically 4.5–6.5 cm wide according to Kawasaki 1993), as 120 Acta Phytotax. Geobot. Vol. 69

Table 1. Comparison of characters of flowers and leaves among Cerasus kumanoensis, sp. nov., C. jamasakura var. jamasakura and C. leveilleana. Characters C. kumanoensis C. jamasakura C. leveilleana Peduncle length (mm) 1–4 (–10) 5–15 1–15 Petal color pink (to white) white white to pink Flowering period* Mid Mar. to early Apr. Early to mid Apr. Mid to late Apr. Bract figure obovate narrowly ovate broadly obovate Flower number per inflorescence 1–2 (–3) 2–4 2–3 Leaf blade** shape narrowly ovate narrowly elliptic broadly obovate Leaf blade** length (cm) 4–8 5–9*** 6–12*** Leaf blade** width (cm) 1.8–3.6 3–4*** 3–6*** Leaf margin roughly serrate acutely serrate roughly serrate Lower surface of leaf pale green glaucous pale green Petiole and pedicel glabrous glabrous hairy * Flowering period observed in towns of Kozagawa and Kushimoto, Wakayama Prefecture, Japan, in 2017. See text. ** Leaf blade observed on short shoot. *** Kawasaki (1993). shown in Fig. 1G. The length and width of the leaf jamasakura did not overlap in my observations. blade on the long shoots in Cerasus differ dis- In individuals observed in detail, the flowering tinctly from those on short shoots (Oohara 2009), periods of surrounding individuals of the two and most references provide both data of long taxa also did not overlap. As C. leveilleana shoots and short shoots. I refer to the sizes given blooms later than C. jamasakura (Miller-Rushing in Kawasaki (1993) that is based only on short et al. 2007), C. kumanoensis and C. leveilleana shoots. Additionally, C. kumanoensis is distin- also differ in flowering period and possibly do not guished by its roughly serrate leaf margin (Fig. cross with each other. Cerasus jamasakura, how- 2G) and pale green lower leaf surface (Fig. 1G), ever, blooms later in this area than in some adja- characters that in C. jamasakura are acutely ser- cent places. For example, in late April, when C. rate and glaucous, respectively. Cerasus kuma- jamasakura blooms in Kozagawa, C. jamasakura noensis is similar to C. leveilleana, but is distin- in nearby Kamitonda has already finished flower- guished by its glabrous petiole and pedicel (Fig. ing. Further studies are needed to determine the 1B, 2A, H). effectiveness of seasonal isolation between C. ku- Another remarkable feature of Cerasus kuma- manoensis and C. jamasakura. noensis is its flowering period. Within its natural As a result of field surveys and examination of range C. kumanoensis blooms earlier than C. ja- specimens in the Makino Botanical Garden (MBK), masakura. The flowering period in 2017 of five Tokushima Prefectural Museum (TKPM), Osaka individuals of C. kumanoensis and C. jamasaku- Museum of Natural History (OSA) and Wakaya- ra, and one cultivated plant of C. × yedoensis ma Prefectural Museum of Natural History (Matsum.) Masam. et Suzuki 'Somei-yoshino' in (WMNH), a new taxon, Cerasus kumanoensis, the towns of Kozagawa and Kushimoto, Wakaya- was confirmed to occur only within Mie, Nara ma Prefecture, are shown in Fig. 3. These indi- and Wakayama Prefectures. New specimens that viduals were near each other (horizontal distance I collected are preserved in TFA (herbarium of within 1,700 m, altitude 20–120 m), and the envi- Tama Forest Science Garden, Forestry and Forest ronment related to flowering period, such as the Products Research Institute, Japan). Since it has mean temperature between 11 February and 10 been thought that only C. jamasakura var. jama- May in 2017 (6.6 °C), appeared to be the same. sakura and C. leveilleana occur in the southern The flowering periods of C. kumanoensis and C. Kii Peninsula (Murata 2004, Morimoto 2011), in- June 2018 Katsuki — Cerasus kumanoensis, A New Species from Japan 121 dividuals of Cerasus kumanoensis have often Prunus antiqua Miyoshi (1922) from Nara Pre- been identified as one of them (e.g. WMNH fecture, it was treated as a cultivar of C. leveille- 13705 and 23483 as C. jamasakura var. jama- ana by Kawasaki (1993). sakura, and OSA 240450 as C. leveilleana). Since more than 50 names have been published among C.serrulata and related taxa from Taxonomic treatment eastern Asia (Ohba 2001), the relationship between them and C. kumanoensis must be exam- Cerasus kumanoensis T. Katsuki, sp. nov. — ined. Prunus superflua Koidz. (1932) has narrow Figs. 1 & 2. leaf blades (6–11 cm long, 2.3–3.8 cm wide) and Similar to C. leveilleana (Koehne) H. Ohba, but distin- in general appearance is similar to C. kumanoen- guished by narrowly ovate and smaller leaf blades (4–8 × sis, but the syntypes (Y. Nabeshima s.n., 15 Apr. 1.8–3.6 cm in C. kumanoensis vs. 6–12 × 3–6 cm in C. 1932, KYO & TI; G. Koidzumi s.n., 17 May 1932, leveilleana), earlier flowering period and glabrous peti- oles and pedicels (Table 1). KYO) collected in Fukuoka Prefecture, Kyushu, Typus. JAPAN, Honshu, Wakayama Pref., Kozagawa, have leaves with acutely serrate margins and nar- Ikenoyama, alt. 40 m, 21 Mar. 2017, T. Katsuki s.n. (holo- rowly ovate bracts, which support Ohba’s (2001) : TI 00012970. Iso-: TFA HDA-000256–258, TNS treatment of it as individual variation within C. 1284055) jamasakura. Six species, varieties or subvarieties have Trees, deciduous, to 16 m tall (flowering well been published from the Kii Peninsula and its even when less than 8 m tall), DBH up to 0.3 m. surroundings, but none of them corresponds to C. Bark purplish brown, almost smooth; lenticels kumanoensis. Holotype specimens of Prunus distinct, horizontal; young branches yellowish mutabilis Miyoshi var. dilatata Nakai (1950) (K. brown, lustrous, glabrous, extending slightly hor- Torii s.n., 30 Oct. 1949, TNS 81083) and Prunus izontally. Leaves alternate, reddish brown or toriwii Nakai (1953) (K. Torii s.n., 15 Apr. 1951, green when young, appearing after flowering, TNS 86156) from Aichi Prefecture have leaves petiolate; petiole 14–20 mm long, usually gla- with acutely serrate margins and narrowly ovate brous; blade narrowly ovate, 4–8 cm long, 1.8– bracts. This supports Ohba’s (2001) treatment of 3.6 cm wide, base rounded to obtuse, margin sim- them as representing individual variation within ply or doubly roughly serrate, serrations with an C. jamasakura. Makino (1906) and Makino apical gland, apex caudate-acuminate, upper sur- (1928) described Prunus pseudo-cerasus Lindl. face with sparse soft hairs, lower surface gla- var. spontanea Maxim. subvar. humilis Makino brous and pale green, slightly lustrous, lateral and Prunus ogawana Makino from Kochi Pre- veins 5–8 pairs, with trichomes in vein axils; api- fecture. The narrowly elliptic leaves with acutely cal part of petiole or base of blade with a pair of serrate margins of the syntypes of the former (T. wart-like glands; stipules lanceolate, incised ser- Makino s.n., 1889, MAK 223123, T. Makino s.n., rate. Bud scales sticky, outer surface glabrous, in- Jun. 1893, 223124) and the holotype of the latter side with hairs. Inflorescences corymbose, 20–36 (T. Makino s.n., 17 Jun. 1927, MAK 225657) sug- mm across, 1- or 2- (or 3)-flowered, axillary, usu- gest that both taxa from Kochi Prefecture are C. ally on previous year’s short shoots and some- jamasakura as treated by Ohba (2001). A syntype times on long shoots; peduncle 1–4 mm long to of Prunus pseudo-cerasus Lindl. var. jamasaku- sometimes over 10 mm at the end of flowering, ra Makino subvar. pubescens Makino (1908) (S. glabrous; pedicel 6–24 mm long, usually gla- Matsuda s.n., Apr. 1902, MAK 223105) from brous; bracts obovate, ca. 5 mm long, incised ser- Nara Prefecture has broadly obovate bracts and rate with a gland. Flowers hermaphroditic; hy- hairy pedicels, which support Ohba’s (2001) panthium glabrous, reddish purple, tube campan- treatment of it as a synonym of C. leveilleana. Al- ulate, slightly broadened apically, 4–8 mm long; though I have not seen authentic specimens of calyx lobes ovate or narrowly ovate, ca. 5 mm 122 Acta Phytotax. Geobot. Vol. 69 A B

C D E

F G

0 50 mm

Fig. 1. Cerasus kumanoensis, sp. nov. A, shape of tree in full bloom (in Kumano on 9 Apr. 2017, TFA HAD-000288); B, hy- panthium and calyx lobes [in Kozagawa on 21 Mar. 2017, TI00012970 (holotype)]; C–E, flower (C in Kumano on 9 Apr. 2017, TFA HAD-000295, D in Kushimoto on 21 Mar. 2017, FA HAD-000213, E in Kumano on 14 Mar. 2017, TFA HAD- 000190); F, mature fruit (in Kumano on 28 May 2017, TFA HAD-000295); G, leaves on short shoot (TI00012971). June 2018 Katsuki — Cerasus kumanoensis, A New Species from Japan 123

B E 1mm 3mm

1mm 1mm F

A H 1mm 3mm

1mm 3mm G D 3mm

Fig.F ig2.. 2Cerasus. Cerasus kumanoensis kumanoensis, sp. nov., sp.A, flower nov. (petalsA, flower removed); (petals B, longitudinal removed); section B, of longitudinalflower (petals removed); section C,of calyx flower (petalslobe; D, petal;removed); E, bract; C,F, bud calyx scale; lobe; G, margin D, petal; of mature E, leafbract; (upper F, surface);bud scale; H, leaf G, base margin and petiole; of mature I, stone. leafDrawn (upper fromsurface); isotype H, (TNS leaf 1284055) base andand paratype petiole; (TNS I, stone. 1284056) Drawn by K. Hamasaki. from isotype (TNS 1284055) and paratype (TNS 1284056) by K. Hamasaki. - 16 - 124 Acta Phytotax. Geobot. Vol. 69

C. k. a b c d e C. j. f g h i j C. y.

1 March 11 21 1 April 11 21 1 May 11

Fig. 3. Flowering period (dashed line) and full flowering period (bold line) of Cerasus kumanoensis, sp. nov. (a–e), C. jamasakura (f–j) and planted C. × yedoensis ‘Somei-yoshino’ observed in 2017 at Kozagawa and Kushimoto Town, Wakayama Prefecture, Japan. Fig. 3. The blossom period (dashed line) and the full blossom period (bold line) of Cerasus kumanoensis, sp. nov. (a–e), C. jamasakura (f–j) and planted C. × yedoensis ‘Somei- yoshino’long, margin observed entire or in serrate,2017 spreading at Kozagawa at anthe- andPrefecture,Kushimoto Kami-kitayama Town, Wakayama Village, Shimo-kita Prefecture,- Japan. sis. Petals pink or sometimes white and slightly yama Village and Totsukawa Village in Nara pink, narrowly to broadly elliptic, 10–20 mm Pref., and Owase City, Kumano City, Mihama long, 6–16 mm wide, base widely cuneate, apex Town and Kiho Town in Mie Prefecture These emarginate. Stamens ca. 30, slightly shorter than localities are at 0 to 800 m elevation. Cerasus ku- style; filaments glabrous; pistil glabrous, 12–16 manoensis typically grows in young secondary mm long. Fruits globose, glabrous, 6–8 mm forests alongside other deciduous broadleaved across, blackish purple when mature, taste slight- trees. It is occurs more on ridges and slopes, less ly bitter; stone flat, ovoid, 5–6 mm long. in valleys and lowlands. It is common in mountainous areas inland and also in coastal locations Phenology. Coastal individuals (alt. 0–100 m) to the south. bloom earliest in late February whereas individuals in mountainous regions (alt. 600–800 m) Japanese name. Kumano-zakura. English bloom in late April. Foliation and seed germina- name. Kumano cherry. tion take place slightly after flowering. Fruiting from mid May to early June. Etymology. The species epithet kumanoensis refers to old regional name of the distribution Distribution and habitat. Cerasus kumanoen- area, Kumano. sis is widely distributed in the southern part of the Kii Peninsula (Fig. 4). Specific localities are Notes. Cerasus kumanoensis is morphologi- Hidakagawa Town, Tanabe City, Shirahama cally distinct from C. jamasakura and C. leveil- Town, Susami Town, Kushimoto Town, Kozaga- leana. The classification of Cerasus in different wa Town, Nachi-katsuura Town, Taiji Town, parts of the world, however, is inconsistent. For Shingu City and Kitayama Village in Wakayama example, Kuitert (1999) and Chang et al. (2007)

- 17 - June 2018 Katsuki — Cerasus kumanoensis, A New Species from Japan 125

E 135° E 136° E 137° N 34°40’

N 34°00’ E 130° E 140°

N 40°

N 30°

N 33°20’

Fig. 4. Locality of holotype (circle), localities of paratype (multiplication sign) and estimated distribution area (dashed line) of Cerasus kumanoensis, sp. nov.

Fig.4. The locality of holotype (circle), the localities of paratype (multiplication sign) and do not treat Cerasus jamasakura as a species. To cation of these taxa, including C. kumanoensis. clarifyestimated this confusion, distribution it is area necessary (dashed to use line) mo of- Cerasus kumanoensis, sp. nov. Paratypes. JAPAN, Honshu, Wakayama Pref., Koza- lecular methods and population genetics and to gawa, Ikenoyama, alt. 40m. 28 Apr. 2017, T. Katsuki s.n. examine the nomenclature. The genetic variation (TI I00012971, TFA HDA-000310–315, TNS 1284056); within the domesticated populations of C. jama- Hidakagawa, Sogawa, 27 Apr. 2017, T. Katsuki KMN-212 sakura in Japan was revealed in recent years (TFA HDA-000308); Kushimoto, Mt. Kasane, 21 Mar. (Tsuda et al. 2009), but the relationship with C. 2017, T. Katsuki KMN-140 (TFA HDA-000213); Na- chikatsuura, Myohozan, 22 Mar. 2016, T. Katsuki KMN- jamasakura var. chikusiensis (Koidz.) H. Ohba 061 (TFA HDA-000028); Susami, Esumi, 8 Sep. 2016, T. on Kyushu and C. leveilleana and C. serrulata in Katsuki SSM-07 (TFA HDA-000172); Tanabe, Hongu, China have not been examined. Although it is Yunomine, 29 Mar. 1994, S Yamamoto 8208 (WMNH possible to identify the taxa of Cerasus in Japan 23483); Tanabe, Ryujin, Mitsumata-hashi, 23 May 1992, using SSR markers (Kato et al. 2014), their phylo- A Yamamoto s.n. (WMNH 13705); Tanabe, Ryujin, Yasui, 6 Sep. 2016, T. Katsuki RYG-10 (TFA HDA-000139); Ta- genetic relationships have not been determined. nabe, Yasukawa, 6 Sep. 2016, T. Katsuki RYG-13 (TFA The possibility of a hybrid origin for C. kuma- HDA-000142); Mie Pref., Kumano, Fudatate Pass, 9 Apr. noensis must also be considered, but natural hy- 2017,- 18 T. - Katsuki KMN-198 (TFA HDA-000295); Kumano, brid swarms in Cerasus in Japan have not been Kamikawa, 14 Mar. 2017, T. Katsuki KMN-116 (TFA examined genetically. Further studies are there- HDA-000190); Kumano, Kiwa, Itaya, 9 Apr. 2017, T. Kat- suki KMN-189 (TFA HDA-000288); Kumano, Kiwa, fore needed to determine the taxonomic classifi- Nunobiki-no-taki, 21 Jul. 2016, T. Katsuki KMN-016 126 Acta Phytotax. Geobot. Vol. 69

(TFA HDA-000097); Owase, Hachiman tunnel, 21 Apr. Kawasaki, T. 1993. Flowering Cherries of Japan. Yama- 2017, K. Okuda s.n. (TFA HDA-000251); Nara Pref., Ka- kei Publishers, Tokyo. (in Japanese). mikitayama, Namegodani, 29 Apr. 2017, T. Katsuki Koehne, E. 1912. Prunus. In: Sargent, C. S. (ed.) Plantae KMN-239 (TFA HDA-000346); Totsukawa, Asahi, 30 Wilsonianae part II: 196–282. University Press, Apr. 2017, T. Katsuki KMN-265 (TFA HDA-000368); Tot- Cambridge, Massachusetts. sukawa, Seinishigawa, 3 Aug. 2006, N. Morimoto 8178-2 Koidzumi, G. 1932. Contributiones ad Cognitionem Flo- (OSA 240450); Totsukawa, Shiratani, 29 Apr. 2017, T. rae Asiae Orientalis. Acta Phytotax. Geobot. 1: 164– Katsuki KMN-232 (TFA HDA-000339). 176. Makino, T. 1906. Observations on the flora of Japan. Bot. Mag. (Tokyo) 20: 37–45. Makino, T. 1908. Observations on the flora of Japan. Bot. I thank Ms. Y. Yamashita, Mr. T. Hogen, Mr. K. Tanoue Mag. (Tokyo) 22: 93–102. and Mr. S. Jyoudo of the Wakayama Prefectural Forestry Makino, T. 1928. A contribution to the knowledge of the Experiment Station, Mr. K. Okuda and Mr. M. Nakamura flora of Japan. J. Jap. Bot. 5: 11–14. of the Mie branch, Japan Tree Doctors Association, Mr. Miller-Rushing, A. J., T. Katsuki, R. B. Primack, Y. Ishii, K. Jinbo and Mr. O. Hashino of the Nanki Forestry Asso- S. D. Lee & H. Higuchi. 2007. Impact of global ciation, the staff of the Kozagawa Town Office, Mr. H. warming on a group of related species and their hy- Sato in Kozagawa Town, the staff of the Kumano City Of- brids: cherry tree (Rosaceae) flowering at Mt. Takao, fice and Mr. K. Okada in the Wakayama Prefectural Of- Japan. Amer. J. Bot. 94: 1470–1478. fice for field surveys, Ms. A. Naito (WMNH), Mr. D. Sa- Miyoshi, M. 1922. Untersuchungen uber Japanische kuma (OSA), Ms. S. Fujii and Dr. K. Fujikawa (MBK), kirschen II. Bot. Mag. (Tokyo) 36: 1–14. Mr. Y. Ibaragi and Mr. M. Ogawa (TKPM), Dr. H. Ikeda Morimoto, N. 2011. Naraken Jyumoku Bunpushi. Self- and Ms. A. Shimizu (TI), Dr. A. Ebihara (TNS), Dr. H. publishing. (in Japanese). Nagamasu (KYO) and Dr. N. Murakami (MAK) for their Murata, G. 2004. Kinki-chiho Shokubutsushi. Osaka generous support in the herbarium, and Ms. K. Hamasaki Natural History Center, Osaka. (in Japanese). for the beautiful illustrations. Nakai, T. 1950. Contributions to knowledge of flowering plants. Bull. Natl. Sci. Mus. Tokyo 29: 71–98. Nakai, T. 1953. Opera phytologica novissima. Bull. Natl. Sci. Mus. Tokyo 33: 1–30. References Ohba, H. 2001. Cerasus. In: Iwatsuki, K., D. E. Boufford & H. Ohba (eds.), Flora of Japan vol. IIb , pp. 128– Chang, K. S., C. S. Chang, T. Y. Park & M. S. Roh. 2007. 144. Kodansha, Tokyo. Reconsideration of the Prunus serrulata complex Ohba, H. & M. Saito 2000. A new variety of Cerasus sar- (Rosaceae) and related taxa in eastern Asia. Bot. J. gentii (Rehder) H.Ohba found at Mt. Shiraiwa-yama, Linn. Soc. 154: 35–54. Miyazaki Prefecture, Kyushu, the southern limit of Ikeda, H., H. Iketani & T. Katsuki. 2017. Rosaceae. In: distribution of the species. J. Jap. Bot. 75: 370–371. Ohashi, H. Y. Kadota, J. Murata, K. Yonekura & H. Ohwi, J. 1953. Flora of Japan. Shibundo, Tokyo. Kihara. (eds.), Wild Flowers of Japan, revised new Oohara, T. 2009. The Handbook of Flowering Cherries in edition 3: pp. 23–88. Heibonsha, Tokyo. (in Japa- Japan. Bun-ichi Co., Ltd., Tokyo. (in Japanese). nese). Tsuda, Y., M. Kimura, S. Kato, T. Katsuki, Y. Mukai & Y. Kato, S., A. Matsumoto, K. Yoshimura, T. Katsuki, K. Tsumura. 2009. Genetic structure of Cerasus jama- Iwamoto, T. Kawahara, Y. Mukai, Y. Tsuda, S. Ishio, sakura, a Japanese flowering cherry, revealed by nu- K. Nakamura, K. Moriwaki, T. Shiroishi, T. Gojobori clear SSRs: implications for conservation. J. Pl. Res. & Y. Yoshimaru. 2014. Origins of Japanese flowering 122: 367–375. cherry (Prunus subgenus Cerasus) cultivars revealed Wilson, E. H. 1916. The Cherries of Japan. University using nuclear SSR markers. Tree Genet. Genomes. Press, Cambridge, Massachusetts. 10: 477–487.

Received June 18, 2017; accepted January 1, 2018