Thunbergia hossei Clarke (1907: 64)

Do, Van Hai, Nguyen, Thu Thuy, Bui, Hong Quang, Duong, Thi Hoan, Choudhary, Ritesh Kumar & Deng, Yunfei, 2025, Notes on the genus Thunbergia (Acanthaceae) in Vietnam, Phytotaxa 697 (3), pp. 255-264 : 256-260

Thunbergia hossei Clarke (1907: 64) ( Figs. 1–2 )

Type: — THAILAND. Chiang Mai, Doi Suthep , 31 December 1904, C. C. Hosseus 276 (lectotype, designated here: M [M-0168571];

isolectotypes: BM [ BM 001252169!], C [C10005232!], E [E00742976], K [K000838908!], L [L.2845326!], P [P03588467!,

P03588469!]). Image of lectotype available at http://plants.jstor.org/stable/10.5555/al.ap.specimen.M0168571.

Description: Vines to 7 m long or more. Stem terete, twining, pubescent, soon glabrescent. Leaf blade ovate to lanceolate, 5–15 × 2‒10 cm, both surfaces glabrous, palmately 5-veined, base rounded to weakly cordate, margin obscurely dentate or sometimes entire, apex shortly acuminate abruptly narrowed into an obtuse apex; petioles 1.5‒3.5 cm, pubescent, gradually shorter upwards and sessile towards the top. Inflorescence of pendulous axillary racemes, 6– 11 cm long; peduncles 1–2 cm, pubescent; bracts opposite, ovate to lanceolate, green, sometimes with purple streaks, 14‒20 × 8–12 mm, abaxially pubescent, adaxially puberulent, base cuneate to rounded, margin dentate, 3‒5 veins arising from the base of the blade, apex acute or shortly acuminate; bracteoles 2, ovate to lanceolate, dark purple, 18–21 × 8–11 mm, pubescent on both surfaces, base rounded to truncate, margin entire, longitudinally 5‒7-veined, apex acute or mucronate, abaxially pubescent, adaxially puberulent; pedicels 9–10 mm, accrescent to 11 mm in fruit; calyx sinuate rim-like, unlobed, ca. 0.5 mm long, sometimes 1‒2-lobed, lobes linear, 1‒2 mm long, pubescent. Corolla yellow-brown, 4‒4.5 cm long, tube yellowish brown, 3.5‒4.0 cm long, slightly enlarged tube and obliquely truncate above, outside pubescent and glandular hairs, inside glabrous, 5-lobed, lobes broadly oblong to elliptic, four upper lobes yellowish brown, subequal, emarginate, ca. 1.5 cm long, one lower lobe yellowish brown, emarginate, longer than upper lobes. Stamens 4, didynamous, included, inserted at the middle of corolla tube; filaments glabrous, flattened, filaments of the shorter pair 12‒13 mm long, longer pair 13‒14 mm long, anthers 2-thecous, thecae oblong, parallel, held at different height, trichomes along the line of dehiscence and base of thecae, anthers of the shorter pair 5‒6 mm long, spurred at the base of upper one for ca. 3 mm long, lower one hairy and muticous at base, anthers of the longer pair 5–6 mm long, both spurred at base for 3‒3.5 mm long; disk thick, annular, yellow, 1.5‒2 mm long; ovary ovoid, ca. 3 × 2.5 mm, densely white-pubescent, 2-locular with two ovules per locule, style 4.2–4.5 cm long, pubescent, stigma whitish-green, 2-lobed. Capsule beaked, basal part 9‒12 × 11–15 mm, beak 1.8–2.2 cm long, pubescent, 4- seeded, seeds compressed, ovate in outline, 6‒7 cm in diameter, verrucose on the surface.

Phenology: —Flowering and fruiting from November to March.

Habitat and ecology: — Thunbergia hossei is currently known from a few locations in the Central Highlands of Vietnam. It climbs on shrubs and small trees in the evergreen broad-leaved forest, at an elevation of 600–1000 m a.s.l.

Distribution: — Laos, Myanmar, Thailand and newly recorded in Vietnam (Kon Tum Province: Dak Glei, Dak To and Sa Thay District; Gia Lai Province: Chu Pah, KBang, Mang Yang District; Dak Lak Province: Krong Bong District).

Remaining syntypes examined: — THAILAND. Chiang Mai, Doi Suthep, 5 February 1905, C. C. Hosseus 425a (M [M-0168572, digital image!]).

Additional specimens examined:— VIETNAM. Dak Lak Province: Krong Bong District, Hoa Le commune, 23 December 1979, Ha Thi Dung 517 (HN); ibid., 23 December 1979, Tran Dinh Ly 845 (HN), Nguyen Thi Nhan 706 (HN); Gia Lai Province: Chu Pah District, Gia Lu village, 11 December 1985, B. B. Dopodpeeb, H. H. Athaytob, N. T. Ban, V. X. Phuong LX-VN 2444 (HN); Mang Yang district, A Yun commune, elev. ca. 980 m, 14°12’41.8”N, 108°19’08.3”E, 29 February 2012, Do Van Hai et al. KNP 758 (HN); ibid., 16 December 2022, Bui Hong Quang Q 28 (HN); ibid., 17 December 2022, Bui Hong Quang, Tran Duc Binh DVH 423 (HN); ibid., Chu Ta Moc village, 30 November 1978, Ha Van Tue 108 (HN); KBang District, Dong commune, 8 March 2011, T. T. Bach, D. V. Hai, B.H. Quang, H.M. Tam, S.D. Thuong PTV 691 (HN); ibid., 10 March 2011, T. T. Bach, D. V. Hai, B.H. Quang, H.M. Tam, S.D. Thuong PTV 702 (HN); KBang District, Son Lang commune, 4 December 1978, Vu Xuan Phuong 827 (HN); Kon Tum Province: Dak Glei District, about 12 km to North of Dak Glei town (24 km by road), near Mang Khen village, 17 November 1995, L. Averyanov, N. T. Ban, A. Budantzev, L. Budantzev, N. T. Hiep, D.D. Huyen, P.K. Loc, G. Yakovlev VH 1772 (HN); ibid., about 7-8 km to the South of Dak Glei town on Dak Poko river near Dak Tung village, 3 December 1995, L. Averyanov, N. T. Ban, A. Budantzev, L. Budantzev, N. T. Hiep, D.D. Huyen, P.K. Loc, G. Yakovlev VH 2232 (HN, P); ibid., 15 January 1947, E. Poilane 32696 (P); Dak To District, 20 November 1946, E. Poilane 35566 (P); Sa Thay District, Dak Pok village, 19 November 1978, Le Kim Bien 851 (HN); ibid., Mo Rai commune, 15 November 1978, Nguyen Huu Hien 454 (HN). THAILAND. Chonburi: Pong Liang, Pong Nam Rawn, 160 m, 9 May 1956, T. Smitinamd 3353 (K). Chaiyapum: Nawng, Bua Deng, 300 m, 3 March 1931, A.F.G. Kerr 20313 ( ABD). Chiang Mai: Pong Dueat Nat. park, ca. 55 km NNE of Chiangmai; km 40 onq the Pai road 1095, 5 km to NE, secondary evergreen forest rich in bamboo, along stream, waterfall and hot springs, 19°8’N, 98°45’E, 600 m, Flowers orange, 26 November 1993, K. Larsen, Supee S. Larsen, Chr. T. Norgaard, K. Pharsen, P. Puudjaa, and W. Uerchirakan 44869 ( AAU); Doi Chiengdao, 19 December 1931, Put 4402 ( ABD, K); Doi Sutep, 1100 m, 30 September 1949, Phloenchit Suvarnakoses 58 (K); Me Kang R bank below near Sap Hat, Chawntawng District, 720 m, 15 January 1936, H.B.G. Garrett 1044 ( ABD, K); Me Kang, Sap Hat, 16 January 1936, H.B.G. Garrett 1047 (K); Me Kang, Sap Hat, c. 780 m, 17 January 1936, H.B.G. Garrett 1050 (K); Me Na Lao, Doi Chiangdao, 650 m, 13 December 1951, H.B.G. Garrett 1372 (K); Doi Sootep, 660- 700 m., 31 December 1904, C.C. Hosseus 276 (K); Doi Sutep, 2200-2300 ft, 2 January 1919, A.F.G. Kerr 513 (K 2 sheet); Wat Thamsaohin Phyanak, Maesai District, 550 m, 14 February 1983, Hiroshige Koyama, Hiroshi Terao & Thawatchai Wongprasert T-33506 (K). Loi: Phu Luang , ca. 1300 m, Dee Bunpheng 990 (K); Ban Na Luang , 17º0’N, 101º40’E, ca. 300 m, 16 Janaury 1970, C.F. van Beusekom, C. Phengklai 3033 (E). Nakhon Ratchasima: Pak Chong, 300 m, 30 December 1923, A. MArcan 1547 ( ABD); Khao Yai National Park, 22 October 1970, T, Smitinand 11343 (K); Khao Yai National Park, Wang Ta Kong, 14º45’N, 102ºE, 650 m, 21 October 1969, C.F. van Beusekom & C. Phengklai 1805 (E); Katok, Korat, ca. 200 m, 1 January 1923, A.F.G. Kerr 8196 ( ABD, E, K); Ban Ta Chang, Korat, 24 December 1930, Put 3500 ( ABD, K). Nan: Amphoe Thung Chang: Ban Huai Sataeng NW of Road 1080, c 3 km South of the Laotian border, 19° 33’ N 100° 53’ E, 500 m, Along trail through degraded dipterocarp-Fagace forest and in dried out bed of small watercourse surrounded by dry evergreen forest, Flowers orange, 20 November 1993, K. Larsen, Supee S. Larsen, Chr. T. Norgaard, K. Pharsen, P. Puudjaa, and W. Uerchirakan 44668 ( AAU).

Phetchabun: Pine Grove , 900 m, 6 January 1960, T. Smitinand & E.C. Abbe 6323 (K) ; Lom Kao, Nam Nao , ca. 800 m, 26 December 1952, Dee Bunpheng 635 (K) ; Thung Salaeng Luang National Park, Wang Thong District , 500-550 m, in evergreen forest, 28 December 1982, Hiroshige Koyama, Hiroshi Terao & Thawatchai Wongprasert T-31879 (K) .

Prachin Buri: Bupram, Krabin, ca. 100 m, 3 January 1925, A.F.G. Kerr 9822 (ABD, K). Phitsanulok: Phitsanulok District, Tung Salaeng Luang National Park, 300-600 m, 12 december 1965, M. Tagawa & N. Fukuoka T2116 (K).

Phrae: Prae, Pokalong , 800 ft., 12 December 1912, Luang Vanpruk 352 (K) ; Mae Khaem Stream, 18º07’N, 100º09’E, 440 m, 5 January 1972, C.F. van Beusekom, C. Phengklai, R. Geesink & B. Wongwan 4631 (K). MYANMAR. Shan State: nearr Tapot , 3500 ft, January 1910, W.A. Robertson 86 (K) ; Kachin State: Bhamo District, Kaukkwe Valley , November 1912, J.H. Lace s.n. (E) ; Myikyina District , 16 November 1925, C.E. Parkinson 327 ( FHO, K) ; Myitkyina District, Kokaung , 15 January 1927, R. N. Parkinson s.n. (K) ; Myitkyina District, Tagwin , 16 November 1925, C.E. Parkinson 327 (K) ; Shanang, Tiggaing to Singon , November 1908, J.H. Lace 4409 (E, K) ; Mandalay Region: Ruby Mines District , January 1910, J.H. Lace 5220 (E, K) ; Ruby Mines District, 400 ft., 21 January 1910, J.H. Lace 5061 (E, K). LAOS. Khammouan: Nam Theun, Kaeng Luang , l 17º45’46”N, 105º20’21”E, 555 m, 3 November 2005, M.F. Newman, P.I. Thomas, K.A. Amstrong, K. Sengdala, V. Lamxay LAO837 (E, L) .

Conservation status:— In Vietnam, the newly recorded species was collected from several localities in provinces located in the central highlands, such as Kon Tum, Gia Lai and Dak Lak. Some populations are distributed within the protected areas, such as national parks or nature reserves, but there is no data on population assessments in the field. The species is also widely distributed in Thailand, Myanmar and Laos. Based on our predictions, the species could occur in other locations with similar habitat conditions. Therefore, it may be classified as ‘Data Deficient’ (DD) according to the IUCN Red List Categories and Criteria ( IUCN 2024).

Taxonomic notes: Aside from the brief description in the protologue ( Benoist, 1935), there are just a few further mentions of Thunbergia hossei , such as Kress et al. (2003), Newman et al. (2007), or POWO (2024). This species was originally described from Thailand, and considered by Benoist (1935) to be distinguished from other species by having 4 bracteoles, of which two are oblong to lanceolate and the remaining two are linear in shape. However, after a thorough examination of type material, it is found that this species possesses only two ovate to lanceolate bracteoles and 1‒2 of the linear bracteoles mentioned by Benoist are actually the calyx lobes ( Figures 1H, I , and J).

Typification: — In the protologue of Thunbergia hossei, Clarke (1907) cited two gatherings, C. C. Hosseus 276 and C. C. Hosseus 425a, collected from Doi Suthep, Chiang Mai, Thailand, but no holotype was indicated. Thus, both are syntypes under Art. 9.6 of ICN ( Turland et al. 2018). Nine duplicates in seven herbaria were traced, viz., C.C. Hosseus 276 (BM [BM001252169], C [C10005232], E [E00742976], K [K000838908], L [L.2845326], M [M-0168571], P [P03588467, P03588469]), and C.C. Hosseus 425a (M [M-0168572]). Among the syntypes, the specimen C.C. Hosseus 276 at M (M-0168571) provides the best diagnostic characters, with well-preserved leaves, inflorescence and showing the bracts and bracteoles. Therefore, we designate this specimen as the lectotype. Seven other duplicates are isolectotypes.

Figures

FIGURE 1. Thunbergia hossei. A. Flowering and fruiting branch, B. leaves (adaxial view showing morphological variation), C. Inflorescence, D. Abaxial view of bracts, showing morphological variation, E. Adaxial view of bracts, showing morphological variation, F. Adaxial view of bracteoles showing ovary, G. Abaxial view of bracteoles, H. Flower bud, showing calyx, I. Ovary, disk and calyx, J. Flower in lateral view, K. Flower in front view, L. Corolla in longitudinal section, M. Stamens, N. Theca in dorsal view, O. Theca in ventral view, P. Disk, ovary and style, Q. Stigma (Photos by Do Van Hai and Bui Hong Quang).

FIGURE 2. Thunbergia hossei. A. Fruiting branch, B. Abaxial leaves, showing the variation, C. Infructescence, D. Fresh fruit, E. Dried fruit, F. Fruit outer view, G. Fruit, longitudinal section, H. Placenta with seed, I. Ovary, transverse section, J. Seed, lateral view, K. Seed, dorsal view, M. Seed, ventral view (Photos by Do Van Hai and Vu Anh Thuong).