Holcoglossum clausum Wojtas, C.Bandara & Kumar

Wojtas, K. Philip, Bandara, Champika & Kumar, Pankaj, 2024, A new species of Holcoglossum (Orchidaceae, Aeridinae) from Southern Shan State, Myanmar with taxonomic notes on Holcoglossum himalaicum, Phytotaxa 638 (3), pp. 257-267 : 258-263

Holcoglossum clausum Wojtas, C.Bandara & Kumar , sp. nov.

TYPES: MYANMAR. Shan State, Taunggyi District: Saw Lwin s.n. ( SING0237310 ) ( SING!- Holotype) ; ibidem, Pindaya Township, 1450−1620 m, 30 November 2008, Tanaka et al. 080131 ( MBK, TI! ( TI00070510 ), Paratypes-image seen) ; plant obtained from Thailand and introduced as in vitro culture to Germany , flowered in cultivation, KPW230426-1 ( HEID204659 ) ( HEID!- Paratype, preserved in spirit) ; THAILAND. Chiang Mai Province, Doi Inthanond , 1900 m, GT 8289 (spirit number 9604) ( C!- Paratype, image seen, location according to Seidenfaden (1988: 317), see note below). ( Figures 1 , 2 , 3 ) .

Diagnosis: Holcoglossum clausum is superficially similar to H. himalaicum and H. semiteretifolium . However, H. clausum has subterete leaves, comparatively the shortest stem (up to 4 cm long), comparatively shorter inflorescence (up to 7 cm long) bearing up to 17 flowers, longest pedicel and ovary (1.7 cm long), largest sepals (≥ 7 mm long) and petals (≥ 7 mm long) of all three species, larger midlobe of the labellum (up to 6 mm long, 3.5 mm wide), shorter side lobe (≤ 2 mm long) of white color, spur of intermediate length (up to 1.3 cm long), smaller column (1.5 mm × 1.5 mm) and the plants flower during November–December. Holcoglossum semiteretifolium and H. himalaicum have subterete and semiterete leaves respectively, longer stem (≥ 5 cm long), longer inflorescence (up to 15 cm long) bearing up to 15 flowers in former and up to 39 flowers in latter, shorter pedicel and ovary (≤ 1.5 cm long), smaller sepals (≤ 7 mm long), smaller petals (≤ 7 mm long), shorter midlobe (up to 4 mm long, up to 2.5 mm wide), longer side lobe (≥ 2 mm long) which is yellowish in former and pink in latter, spur shortest in former (0.5–0.6 cm), longest in latter (1.2–1.5 cm), larger column in both (2.0 mm × 2.0 mm) and both species have different flowering time (former in March and latter in October–January) (see Table 1 and Figure 4 ).

Description: Monopodial, epiphytic herb, pendant, roots many, at the base of stem, silvery-grey, rigid and flexuous, creeping and densely appressed to substrate. Stem short up to 4 cm long and 0.7 cm broad; leaves 4–5, subterete, channelled on ventral side, up to 45 cm long, 0.3–0.5 cm wide, acuminate, sheathing at the base, leaf sheath ca 1.8 cm long, clasping the stem. Inflorescence bending to be horizontal, bracteate raceme, up to 7 cm long, rachis up to 4.8 cm, bearing 5–17 flowers. Pedicel with ovary clavate, ca. 3 cm long, 1.0– 1.7 mm in diameter, glabrous, ridged on surface. Floral bracts narrowly triangular, ca. 2.0 mm long, acute. Flowers not widely open, resupinate, ca. 7–8 mm long, ca. 5–6 mm wide, pink or white coloured with darker markings on the dorsal surface along the mid-veins of petals and sepals. Dorsal sepal elliptic, 7.2–7.5 mm long, up to 2.4–2.6 mm wide, obtuse, 5-veined, pink; lateral sepals ellipticovate, slightly oblique, 7.8–9.0 mm long, 4.1–4.2 mm wide, acute, 3-veined, pink; petals elliptic, slightly oblique, 7.1–7.2 mm long, 3.0– 3.1 mm wide, obtuse, 5-veined, pink; labellum 3-lobed, 5.5–6.0 mm long, up to 5 mm wide; midlobe tongue-shaped, 5.5–6.0 mm long, 3.5–3.6 mm wide, succulent, retuse at the apex giving a bilobed look, 5- veined, pink, pointed forwards; side lobes erect, broadly ovate-orbicular, 1.6–1.7 mm long, 1.5–1.6 mm wide, apex broadly obtuse, white; column very short and stout, 1.5 × 1.5 mm, partly hidden by the side lobes of labellum; stigma orbicular to slightly cordate, 1.0 × 0.9 mm; rostellum with two short horns directed upwards; clinandrium round, almost flat, foot absent; spur located at the base of the column, slightly inflated on side, 1.1–1.3 cm long, 1.0– 1.2 mm wide, rounded at the apex, pink, slightly bent forwards; anther cap trapezoid, cucullate, 1.0 mm long, 1.2 mm wide, dark pink, with two lobes inside; pollinarium 1 with two lobes, 1.2–1.4 mm long, 0.8 mm wide, each lobe fabiform, 0.6 mm long, 0.4 mm wide, dark red, with a depression on the outer side; stipe elliptic with recurved margin, broader at the base, narrower above, 0.8 mm long, 0.3 mm wide at base, 0.1 mm wide towards apex, white, translucent; viscidium trapezoid, 0.2–0.4 mm, white, translucent. Fruit not seen.

Other Specimens studied: THAILAND. Mae Hong Son province, Doi Khun Huay Pong, 1800 m, March 1968, GT 7276 (C!- Holotype of H. semiteretifolium , images seen); Chiang Mai Province, Doi Inthanond, 1900 m, LØjtnant & Chalawit 143 (spirit number 9606) (C!, H. semitertifolium , images seen); MYANMAR. Sima, Kachin Hills, 1981 m, January 1900, Shaik Mokim 13 (CAL0000000490, https://ivh.bsi.gov.in/phanerogams-Details/en?link =CAL0000000490&column=szBarcode) (CAL!- holotype of Saccolabium himalaicum , image seen); ibid., December 1899, Shaik Mokim 71, (CAL0000000486, https://ivh.bsi.gov.in/phanerogams-Details/en?link=CAL0000000486&col umn=szBarcode; CAL0000000489, https://ivh.bsi.gov.in/phanerogams-Details/en?link=CAL0000000489&column=s zBarcode) (CAL!- paratypes of S. hamalaicum , images seen); Kachin, Putao, 1220 m, 29 October 1953, F. Kingdon-Ward 21528, (BM000539014, https://data.nhm.ac.uk/object/32e4fd7a-9106-4de8-8f23-bffe66455794/168860160000 0) (BM! H. himalaicum , image seen) BHUTAN. Zhemgang. 18 November 1964, D.B. Deb 424, (CAL0000000487, https://ivh.bsi.gov.in/phanerogams-Details/en?link=CAL0000000487&column=szBarcode) (CAL! - paratype of S. himalaicum , image seen). TAIWAN. S. mountains Koarong-Shiusuisei, 1220 m, 24 May 1912, W.R. Price 551 (K!, H. pumilum , K000891627, image seen). CHINA. Yunnan, Shweli-Salwin divide, 2440 m, November 1924, Forest 26130 (K000891626, http://specimens.kew.org/herbarium/K000891626) (K!- paratype of H.junceum ,image seen), duplicate at E (E00123460, https://data.rbge.org.uk/herb/E00123460) (E!- paratype of H. junceum , image seen); Yunnan, Tengchong County, Jietou municipal, Datang Cun, East of Datang on the Western slope of Gaoligong Shan, 2000 m, 30 October 1998, H. Li, B. Bartholomew & Z. Dhao 11286 ( CAS 629868, https://www.cch2.org/portal/collections/individual/index. php?occid=4662960&clid=0) ( CAS !, H. junceum , image seen); Yunnan, Kunming, 24 November 1980, Z.H.Tsi 0076 (PE00200781, http://nsii.org.cn/2017/specimen.php?id=6475664) (PE! H. junceum , image seen), Yunnan, Lianghe, 10 November 2015, 5331220805 (IMDY0042615, http://nsii.org.cn/2017/specimen.php?id=18358911) (IMDY! H. himalaicum , image seen); INDIA . Between Ukhrul and Tusom Khullen, 21 November 1948, F. Kingdon-Ward 18339 (NY02650866, https://sweetgum.nybg.org/science/vh/specimen-details/?irn=3377419) (NY!, H. himalaicum , image seen); Assam, Karong, Manipur, 1070 m, 25 November 1950, Koelz 27016 (MICH1492888, https://midwestherbaria. org/portal/collections/individual/index.php?occid=30239881&clid=0) (MICH!, H. himalaicum , image seen).

Flowering phenology: Plants in flower were observed in late November (winter, dry season). Plants with pure white flowers were observed in pictures on social media.

Etymology: Derived from Latin clausum meaning closed, referring to the barely opening flowers of the new species.

Distribution: Myanmar (Taunggyi District, Shan State) and Thailand (Doi Inthanon, Chiang Mai province).

Habitat and ecology: Tropical mixed deciduous forest on limestone at 1500–1600 m.

Conservation assessment: Plants are known to occur in Myanmar (Taunggyi) and Thailand (Doi Inthanon) ( Ormerod et al. 2021, Seidenfaden 1988) in the Indo-Myanmar Biodiversity Hotspot. In Myanmar, the plants were observed growing on the branches of trees towards the open areas in a tropical mixed deciduous forest by Tanaka (pers. comm.) (see figure 5). Tanaka also informed us that locals in Shan State collect the plants and grow them at their homes. Plants have been observed to set fruits naturally and most likely recruit too. Plants have also been seen on display or trade on social media (Facebook). The plants in Europe, although procured from Thailand were most probably collected in Myanmar or propagated usings seeds acquired from Myanmar. This implies that the species is in immense threat of collection for its high ornamental value. Extent of Occurrence and Area of Occurrence is calculated in GeoCAT ( Bachman & Moat 2012) as 367 km 2 and 16 km 2 respectively, but, the total number of mature individuals is not known in either country. Due to continuing decline in the number of mature individuals, and presence of 4 location, this species should be best assessed as Endangered [EN B1ab(v)+B2ab(v)] following IUCN Standards and Petitions Committee (2022).

Note: Interestingly, the species was already shown by Seidenfaden (1988: 397, pl. 37A) as a photograph with an erroneous determination as Ascocentrum semiteretifolium Seidenf .. We believe that the specimen GT 8289, deposited at C, is depicted in this photograph. Seidenfaden annotated on the specimen “near semiteretifolium ”. This suggests that he may have recognized it as a distinct species. Nevertheless, it remains unclear why he did not describe it or why it was listed under A. semiteretifolium . However, there is no further information on the container of the specimen or the inlying note. Seidenfaden (1988: 317) cited this specimen in Opera Botanica 95, giving “ Chiang Mai, Doi Inthanond” as its locality. But the second specimen at C, collected by Løjtnant & Chalawit (no. 143) from the same location, represents H. semiteretifolium and not the new species. Initially, we had doubts regarding the origin of GT 8289 from the specified location also because the photograph appears to depict a cultivated plant. However, in December 2023, during the review process of the manuscript, we received images of flowering plants of the newly described species from Doi Inthanon, confirming the occurrence of the new species in Thailand (Phumsaringkharn pers. comm.).

Figures

FIGURE 1. Holcoglossum clausum Wojtas, C.Bandara & Kumar. A. A plant. B. Front view of flower. C. Side view of flower. D. Floral bract. E. Dorsal sepal. F. Petal. G. Lateral sepal. H. Labellum. I. Side view of flower (dorsal and lateral sepal and petal removed). J. Side lobe of labellum. K. Front view of column. L. Pollinarium. M. Dorsal and ventral view of anther cap. [Compilation by C. Bandara, photographs by K.P. Wojtas, based on fresh specimen and paratype: KPW230426-1 (HEID!)].

FIGURE 2. Holcoglossum clausum Wojtas, C.Bandara & Kumar. A. Close up of inflorescence. B. Side view of flower, C. Floral bract. D. Dorsal sepal. E. Petal. F. Lateral sepal. G. Labellum. H. Labellum with spur. I. Side view of labellum. J. Immature fruit. K. Anther cap. [Compilation and photographs by Champika Bandara, based on holotype: Saw Lwin s.n. - SING0237310 (SING!) with permission from SING Herbarium, Singapore Botanic Gardens]

FIGURE 3. Holcoglossum clausum Wojtas, C.Bandara & Kumar. A. A plant. B. Close up of inflorescence. C. Front view of flower. D. Side view of flower. E. Floral bract. F. Dorsal sepal. G. Petal. H. Lateral sepal. I. Labellum. J. Side view of labellum. K. Close up of side lobe. L. Labellum with spur. M. Front view of column. N. Anther cap. O. Pollinarium. [Drawn by Champika Bandara from Saw Lwin s.n. - SING0237310 (SING!-Holotype) and KPW230426-1].

FIGURE 4. Comparison of pink-floweredAsia-mainland Holcoglossum species.A. H.semiteritifolium. B. H. himalaicum. C. H.clausum. [Compilation by C. Bandara, picture of H. semiteretifolium by K. Keller, other pictures by K. P. Wojtas.]