Thrixspermum praetermissum Toolmal, Schuit. & Suddee, 2023

Toolmal, Nopparut, Suddee, Somran, Culham, Alastair, Utteridge, Timothy M. A. & Schuiteman, André, 2023, Taxonomic notes on Thrixspermum (Orchidaceae: Aeridinae), with five new species from Thailand, Phytotaxa 601 (3), pp. 223-262 : 230-235

2. Thrixspermum praetermissum Toolmal, Schuit. & Suddee , spec. nov.

( Figs. 5–7 , 11A–B ).

Type:— THAILAND. Eastern Thailand , Chaiyaphum Province, Phu Khieo Wildlife Sanctuary, Thung Kamang, 07 December 2020, N. Toolmal , B. Buaphong & K. Putaha 07122002 (holotype: TTM-Spirit; isotypes: BKF, QBG) .

Thrixspermum trichoglottis auct. non (Hook.f.) Kuntze: Seidenfaden (1988: 163); Seidenfaden (1992: 408); Huda (2007: 47); Schuiteman et al. (2008: 312); Chen et al. (2009: 469); Xu et al. (2010: 444); Gao & Liu (2014: 1084); Averyanov et al. (2016: 353); Gale et al. (2018: 170); Jin et al. (2019: 213); Misra (2019: 528); Aung et al. (2020: 103); Barbhuiya et al. (2021: 717).

Sarcochilus hystrix auct. non (Blume) Rchb.f.: Grant (1895: 301).

Thrixspermum hystrix auct. non (Blume) Rchb.f.: Ormerod et al. (2021: 229) .

Thrixspermum praetermissum is similar to T. trichoglottis in the elongate stem, mostly oblong leaves, and the 3-lobed lip with pubescent lateral lobes. It can be distinguished from T. trichoglottis by the white tepals (vs. pale yellow tepals), the broader lanceolate to elliptic dorsal-sepal 3–4 mm wide (vs. oblanceolate to elliptic dorsal-sepal 2.5–3.0 mm wide), the broader and longer lateral sepals 10–11 × 4–5 mm (vs. 8–10 × 3.5–4 mm), the broader petals 3.0– 3.5 mm wide (vs. 2.5–3.0 mm wide), the narrow conical spur 3 × 2 mm with distinctly 2-lobed at apex (vs. the broader conical spur 2.5 × 2.0 mm with indistinctly 2-lobed to obtuse at apex), lip with smaller broadly ovate to slightly suborbicular lateral lobes 3.5–4.0 × 2.0– 2.5 mm, apex rounded (vs. obovate lateral lobes, 4–6 × 3.0 mm, apex obtuse), the longer, ovate mid-lobe 1.0 × 1.5 mm, with 1 mm long capitate hairs along the apical margins only, apex erect, recurved and obtuse (vs. mid-lobe broadly triangular 1 × 2 mm, slightly concave only in the basal part, convex apically (0.5 mm), adaxially with capitate hairs but without capitate hairs along the apical margins, apex acute and decurved).

Epiphytic herb. Stems patent, 8–16 cm long, with 18–20 internodes, terete, slightly laterally compressed, curved upwards in upper half, covered with the leaf sheaths, 11–12-leaved, new plants can arise from the original stem; internodes 4.0–10.5 × 1.2–3.6 mm. Roots terete, thick, elongate, 6 cm to more than 35 cm long, 0.2–1.7 mm diam., arising from the basal part of the stem and from nodes near the lowest leaf, not or sparsely branching. Leaf sheaths green, sometimes spotted or suffused with purplish red, slightly bilaterally compressed, longer than the stem internodes. Leaves green, sometimes spotted or suffused with purplish red, patent, elliptic to oblong, 1.8–4.0 × 0.6–1.5 cm, sessile, slightly narrowed towards the base, leaves on the same side of the stem 0.5–1.0 cm apart, dorsiventrally flattened, apex unequally 2-lobed with obtuse lobes, with a small mucro in the middle, thick, rigid, fleshy, coriaceous, the midrib distinct on the abaxial side. Inflorescences four to twelve per plant, patent, racemose, 1–5(10) cm long, long pedunculate, arising from the nodes at the lowest leaves and below the roots, yellowish green; peduncle terete, slightly upwards curved from the middle, 1.5–9.5 cm long, 0.8–2.5 mm diam., with 2 internodes, the basal internode somewhat shorter, 1.2–2.0 mm long, 0.5–0.8 mm diam., the terminal internode swollen distally, 1–3 cm long, broadening to 2.5 mm diam. just below rachis; peduncle scales 2, green, slightly spotted or suffused with purplish red, broadly ovate to triangular, incurved, concave, thickened, slightly boat-shaped, clasping the peduncle, 2–3 × 1 mm, apex acuminate, keeled; rachis relatively short, 5.7–8.0 mm long, depending on the age of the inflorescence, densely 4–7- flowered, with 1–2 flowers open at a time, swollen, 3.7–5.2 mm diam., clearly thicker than the peduncle. Floral bracts quaquaversal, green, slightly spotted or suffused with purplish red, broadly ovate to triangular, incurved, concave, thickened, slightly boat-shaped, strongly clasping the rachis at the base, 3 × 2 mm, apex acuminate. Pedicel-with-ovary pale yellow, cylindrical, 6-grooved, 6–8 mm long, 0.5–1.0 mm diam. Flowers resupinate, opening widely, lasting one day, membranaceous, 1.0– 2.5 cm across; tepals white, lip white, spotted with brownish orange at the basal part of the lateral lobes, at the lip between the lateral lobes, and apical margins of the mid-lobe, the spur with orange warts inside on the back wall which shine through on the outside, column and anther creamy white, pollinia bright yellow, stipe and viscidium creamy white. Dorsal sepal lanceolate to elliptic, 10 × 3–4 mm, concave, slightly boat-shaped, acute, glabrous, 5-nerved, nerves reticulate branching. Lateral sepals lanceolate, 10–11 × 4–5 mm, obliquely dilated at the lower margin, rather concave, slightly boat-shaped, with a low abaxial keel, acute, glabrous, 5-nerved, nerves reticulate branching. Petals oblanceolate, 8–9 × 3.0– 3.5 mm, narrower than the sepals, concave, slightly boat-shaped, apex acute, glabrous, 3-nerved, nerves reticulate branching. Lip rhombic-triangular in outline when spread, oblong in natural position, 3-lobed, 5–6 × 2.5–3.0 mm in natural position, 7–8 mm wide when spread, with a conical, sac-like spur at the base; spur narrowly conical, 3 × 2 mm, apex 2-lobed with obtuse lobes (0.5 × 0.7 mm), inside towards the base of the callus with large, orange, rounded warts, 1 mm diam. and densely covered with fairly long capitate hairs (0.5 mm long); lateral lobes broadly ovate to slightly suborbicular, distinctly shorter than the mid-lobe, 3.5–4.0 × 2.0– 2.5 mm, with rounded apex, erect, curving upwards and clasping the column, densely covered with 0.8–1.0 mm long capitate hairs on both surfaces and along the apical margins; mid-lobe ovate, 1.0 × 1.5 mm, somewhat concave, covered with 1 mm long capitate hairs along the apical margins, rather thick, fleshy, entire, apex obtuse, recurved; lip adaxially between the lateral lobes densely covered with long capitate hairs, glabrous abaxially, a little below the mid-lobe with a cuneate callus 1 mm long, 0.8–1 mm diam., apex bilobulate, decurved, glabrous. Column cylindrical, short, stout, 2 × 1.5 mm, laterally winged; column-foot short, broad, 1.5–2.0 × 1.5–2.0 mm. Anther suborbicular in outline, glabrous, 1.0 × 1.0 mm, the median with a longitudinal ridge. Pollinia in two pairs, those in a pair unequal, ovate, curved; the larger 0.8 × 0.5 mm; the smaller, 0.6 × 0.3 mm; stipe broadly ovate, 0.5 × 0.5 mm, concave along the median, slightly translucent; viscidium transverse-linear, 0.2 × 0.5 mm, bent into a crescent shape, slightly translucent. Fruit yellowish green, narrowly cylindrical, 8 cm long, 2.5–3.5 mm diam., with 6 longitudinal ridges. Described from spirit material.

Distribution:— INDIA . Assam, Arunachal Pradesh and Meghalaya. BANGLADESH. Cox’s Bazar and Chittagong. MYANMAR. Kachin (Mohnyin), Mon (Mawlamyine), Tanintharyi (Dawei, Myeik). CHINA. Yunnan (Xishuangbanna). THAILAND. Northern: Mae Hong Son Province (Sop Ngao), Chiang Mai Province (Fang, Chiang Dao, Mae Taeng), Tak Province (Umphang), Pitsanulok Province (Nakhon Thai); North-Eastern: Phetchabun Province (Nam Nao, Thung Salaeng Luang); Eastern: Chaiyaphum Province (Phu Khieo Wildlife Sanctuary); South-Western: Kanchanaburi Province (Tha Kanun, Wangka, River Kwai, Sai Yok, Kreng Kravia, Sangkhla); Peninsular: Chumphon Province (Chumphon to Ranong), Ranong Province (Lamlieng). LAOS. Vientiane. VIETNAM. Dak Lak (Yok Don), Ninh Thuan (Ninh Phuoc) ( Fig. 26 ).

Phenology:—Flowering in January, February, April, July, August, September, October, November and December (in natural habitat, seventeen records); January, April, September and November (in cultivation, four records). Flowering is probably intermittent throughout the year, as in most species of Thrixspermum .

Habitat and ecology:—Epiphyte in riverine forests, deciduous dipterocarp forest, mixed deciduous forest, forest on limestone, dry evergreen forest, secondary evergreen forest, bamboo forest, at 400–800 m elevation, locally common along streams, waterfalls, hot springs, and in the surrounding zone, growing on trunks or twigs of small trees, such as Psidium guajava L. ( Myrtaceae ), in exposed positions at about 1–3 meters above the ground.

Conservation status:— Thrixspermum praetermissum is a widespread species distributed from North-eastern India , Bangladesh, Myanmar, southern China, Thailand, Laos to southern Vietnam, with an Extent of occurrence (EOO) of 2,288,820.461 km 2 and an Area of occupancy (AOO) of 112.000 km 2. The species is quite common locally with a large number of individuals and is widespread across the northern part of mainland southeast Asia. It is, therefore, assigned the conservation status of Least Concern (LC) according to IUCN criteria.

Etymology:—From the Latin praetermissum , disregarded, in reference to the fact that this common and widespread species has usually been misidentified as T. trichoglottis (Hook.f.) Kuntze.

Vernacular ( Thailand):—Ueang Khao (เอื̊องขาว), Ta Khap Khao (ตะขาบขาว), Ta Khap Khao Pak Lai (ตะขาบขาวปากลาย).

Additional specimens examined:— MYANMAR. Kachin, Mohnyin District, Kurzweil & Saw Lwin KL 2789, 5 May 2010, (SING s.n., not seen), Mon, Mawlamyine District, Parish 107 & 285 (K s.n., not seen), Tanintharyi, Dawei District, Ye Lwin Aung PT-7329, as T. trichoglottis (PE s.n., not seen), Myeik District, Griffith 1006, Kew Distr. 5232 (K s.n.!). THAILAND. Northern: Mae Hong Son Province, Sop Ngao, A.F.G. Kerr 266A, 02 February 1912 (K s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), Chiang Mai Province, Fang District, Seidenfaden & Smitinand GT 2097 (C 8425!, 8360!, 8355!, Seidenfaden 1988: 162 as T. trichoglottis ), Chiang Dao District, Ban Bing Kong, J.F. Maxwell 87-1302, 29 October 1987 (BKF 94558!, CMU 000797!, L 0597319, not seen, L 1540280!), Mae Taeng District, A.F.G. Kerr 266, 14 October 1912 (K s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), N. Toolmal & P. Rakthai 22082001, 22 August 2020 (TTM 0006358!), Pong Dueat, K. Larsen, Supee S. Larsen, Chr. T. Norgaard, K. Pharsen, P. Puudjaa & W. Uerchirakan 44872, 26 November 1993 (AAU s.n.!), Mae Rim District, Queen Sirikit Botanical Garden, Orchid Nursery, S. Pumicong 12, 28 November 2005 (QBG 27088!), C. Glamwaewwong 1127, 29 August 2005 (QBG 25286!), Mueang District, JJ botanical shop, N. Toolmal & A. Promtong 26122002, 26 December 2020 (TTM 0006397!), Tak Province, Umphang District, Umphang Wildlife Sanctuary, Thi Lo Su Waterfall, S. Suddee et al. 4672, 06 April 2014 (BKF s.n.!), Pitsanulok Province, Pitsanulok to Lomsak km 80, Seidenfaden & Smitinand GT 5360 (C 8358!, Seidenfaden 1988: 162 as T. trichoglottis ), Seidenfaden & Smitinand GT 5361, 12 February 1987 (C 8424!, 8394!, Seidenfaden 1988: 162 as T. trichoglottis ); North-Eastern: Phetchabun Province, Nam Nao District, Nam Nao National Park, S. Suddee et al. 1799, 03 July 2003 (BKF s.n.!), Thung Salaeng Luang National Park, Seidenfaden & Smitinand GT 5511, (C 8393!, Seidenfaden 1988: 162 as T. trichoglottis ); South-Western: Kanchanaburi Province, Tha Kanun, A.F.G. Kerr s.n., 23 January 1926 (K s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), Wangka, A.F.G. Kerr 0299, 12 February 1926 (K s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), River Kwai, C. Phengkhlai 292, 21 December 1961 (BKF 113300!), Kostermans, AJGH 733, 24 May 1946 (L 1540281!, Seidenfaden 1988: 162 as T. trichoglottis ), Sai Yok, K. Larsen 8924, 23 December 1961 (C s.n.!), Seidenfaden & Smitinand GT 4323 (C 8392!, Seidenfaden 1988: 162 as T. trichoglottis ), Seidenfaden & Smitinand GT 4324 (C 8362!, Seidenfaden 1988: 162 as T. trichoglottis ), Kreng Kravia, C. Chermsirivathana 1775, 01 February 1971 (BK 256121!), Sangkhla, CP., BN., SS. 3052, 24 February 1975 (BKF 078295!); Peninsular: Chumphon, A.F.G. Kerr 0357, 27 January 1927 (BK 256118!, C s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), Chumphon to Ranong, C. Phengkhlai 1098, 16 September 1965 (BK 42378!), Lamlieng, A.F.G. Kerr s.n., 29 December 1918 (K s.n.!, Seidenfaden 1988: 162 as T. trichoglottis ), Unknown locality, O. Thaithong 546, 07 December 1988 (BCU s.n.!). LAOS. Vientiane Province, route 13 at km 50 towards Luang Prabang, A.D. Kerr 2447 (C 8421!, Seidenfaden 1988: 162 as T. trichoglottis ). VIETNAM. Cao Bang Province, Ha Lang District, Municipality Thang Loi, Vicinities of Lung Sam Village, H.N. Ridley 351, 1953 (BM 000534688!), Dak Lak Province, Yok Don, L. Averyanov & T. Maisak AL 022, 14 August 2015 (LE 01076415!), Ninh Thuan Province, Ninh Phuoc District, Dinh Quang Diep s.n., 01 April 2014 (LE 01067190!), Bien Hoa, F. Evrard 61, 19 October 1920 (P 00324382!).

Taxonomic notes:— Thrixspermum praetermissum is a distinctive species because of the combination of white tepals and a lip mid-lobe with 1 mm long capitate hairs along the apical margin only. It has long been confused with T. trichoglottis , from which it differs in the characters mentioned in the diagnosis, in particular, in the white flowers, the broader sepals and petals, the lip with broadly ovate to slightly suborbicular lateral lobes with rounded apex, the ovate mid-lobe with long capitate hairs along the apical margins, and an obtuse and recurved apex. The two species also have different geographical distribution ranges: T. praetermissum occurs only in the northern part of mainland South-East Asia and tropical Asia, from India , Bangladesh, China, Myanmar, Thailand, Laos to Vietnam, whereas T. trichoglottis can only be found in the southern part of mainland SE Asia and in the Malay Archipelago, from Peninsular Thailand and Malaysia to Borneo ( Sarawak, Sabah) and Java ( Fig. 25 ).

Because of the white flowers with brownish orange spots on the lip, Thrixspermum praetermissum resembles T. pulchellum (Thwaites) Schltr. (Schlechter 1911: 57, based on Cylindrochilus pulchellus Thwaites 1858 –1864[1861]: 307) ( Fig. 12E–F ), a species from Sri Lanka, Thailand (pers. obs. Nopparut Toolmal) and Peninsular Malaysia. However, these species differ in several characters. Thrixspermum praetermissum has elliptic to oblong leaves, distinctly unequally 2-lobed at apex with obtuse lobes (vs. narrowly oblong to oblanceolate, slightly unequally 2-lobed at apex with acute lobes), inflorescences mostly shorter than the leaves or subequal, or rarely twice as long as the leaves (vs. inflorescence always distinctively longer than the leaves). Thrixspermum praetermissum has a lanceolate dorsal-sepal (vs. elliptic to oblanceolate dorsal-sepal), petals 3.0– 3.5 mm wide (vs. petals 2.0– 2.5 mm wide), ovate mid-lobe, 1.5 mm wide, covered with 1 mm long capitate hairs only along the apical margins (vs. broadly triangular mid-lobe, 3.5–4.0 mm wide, adaxially densely covered with 0.3 mm long capitate hairs, abaxially sparsely covered with short capitate hairs, and with longer capitate hairs along the margins (0.5 mm long). The distribution areas are also different: T. praetermissum , as mentioned above, is distributed only in the northern part of mainland South-East Asia and tropical Asia, whereas T. pulchellum has only been recorded from Sri Lanka, Peninsular Thailand and Peninsular Malaysia.

Figures

FIGURE 5. Thrixspermum praetermissum. A. Habit. B. Flower (oblique view). C. Flower (ventral view). D. Flower (front view, closeup). E. Lip (lateral view). F. Lip with warts on the back wall of spur (longitudinal section). G. Lip (adaxial view, natural position). H. Capitate hairs on the lateral lobes apical margins (close-up). I. Dissected perianth. J. Column & column-foot with pedicel (lateral view). K. Column (ventral view). L. Anther with pollinia (ventral view). M. Pollinia (two pairs). N. Stipe & viscidium. (Drawn from holotype, N. Toolmal et al. 07122002, TTM 0006385). Illustration by Phattaravee Prommanut.

FIGURE 6. Thrixspermum praetermissum. A. Flower (oblique view). B. Flower (ventral view). C. Flower (lateral view). D–F. Flower, front view (close-up). G. Dissected perianth. H. Lip, adaxial view (left: natural position; middle & right: spread out). I. Lip, lateral view (left: longitudinal dissection; right: natural position). J. Column & column-foot with pedicel (lateral views). K. Anther with pollinia (left: dorsal view; right: ventral view). L. Pollinia (two pairs). M. Stipe & viscidium. Photographed by C-SEIDENFADEN no. 24-188, 24- 143, 24-144, 24-184, 24-149 reproduced with permission of the Natural History Museum of Denmark (A–E), Pongpol Rakthai (F–J) & Nopparut Toolmal (K–O). Illustration assembled by Yongyuth Rattanasootr. A–E from living collection (C) of Seidenfaden & Smitinand GT 5361, F–J from living collection and K–M from spirit collection of N. Toolmal et al. 07122002 TTM 0006385.

FIGURE 7. Thrixspermum praetermissum. A. Flowers (front view). B. Flower (ventral view). C–D. Flower (oblique view). E. Lip (showing long capitate hairs along the margins of the lateral lobes and the mid-lobe). F. Plant habit. Photographed by Anurak Promtong (A–D. Cultivation), Kurt Keller (E. Cultivation), Nopparut Toolmal (F. Cultivation). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 11. Thrixspermum trichoglottis. A–B. Plant habit. C. Flowers (ventral view). D. Flower (front view). E. Flower (ventral view). F. Fruit. Photographed by Satawan Atdhabhan (A–C. In situ) & Wattana Tanming (D & F. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 12. A comparison of allied species.A–B. Thrixspermum praetermissum. C–D. Thrixspermum trichoglottis. E-F. Thrixspermum pulchellum. Photographed by Kurt Keller (A–B. Cultivation), Wattana Tanming (C–F. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 25. Distribution map of Thrixspermum alboluteum in Thailand.

FIGURE 26. Distribution map of Thrixspermum praetermissum and T. trichoglottis in subtropical and tropical Asia.