Thrixspermum alboluteum Toolmal, Schuit. & Culham, 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 : 225-230

1. Thrixspermum alboluteum Toolmal, Schuit. & Culham , spec. nov.

( Figs. 1–3 , 4A–B ).

Type:— THAILAND. South-Western Thailand, Phetchaburi Province, Kaeng Krachan National Park , Ban Krang Camp, 312 m, 20 December 2020, N. Toolmal , S. Raksue & W. Tanming 20122001 (holotype: TTM-Spirit; isotypes: BKF, QBG) .

Thrixspermum musciflorum auct. non A.S. Rao & J. Joseph: Seidenfaden (1988): 166, Fig. 101, Pl. XVIIb.

Thrixspermum alboluteum is distinguished from T. formosanum by the distinct concave triangular mid-lobe with emarginate apex, covered with long clavate hairs adaxially and in the apical part (vs. indistinct mid-lobe with glandular hairs adaxially), the obliquely obovate lateral lobes 4.0–5.0 mm long with rounded apex (vs. triangular 1.5–3.0 mm long with obtuse apex), bright yellow tepals, lip white, with brownish orange spots on the sac, and with scattered small orange warts inside the sac (vs. white tepals, lip white, marked with pinkish lines, with two orange-yellow bars along the apical margin, and without warts).

Epiphytic herb. Stems patent, 3.5–8.0 cm long, with 5–14 internodes, terete, slightly laterally compressed, curved upwards in upper half, covered with the leaf sheaths, 4–13-leaved; internodes 1.2–4.4 × 1.2–3.6 mm. Roots terete, thick, elongate, 4 cm to more than 30 cm long, 0.5–2.4 mm diam., arising from the basal part of the stem and from nodes opposite the leaves, not or sparsely branching. Leaf sheaths green, spotted or suffused with purplish red, slightly bilaterally compressed, longer than the stem internodes. Leaves green, spotted or suffused with purplish red, patent, narrowly oblong to linear, 12–60 × 3–7 mm, sessile, slightly narrowed towards the base, leaves on the same side of the stem 1.4–7.0 mm apart, dorsiventrally flattened, conduplicate, V-shaped in cross-section, apex unequally 2-lobed with sharply acute lobes, with a small mucro in the middle, thick, rigid, fleshy, coriaceous, the midrib distinct on the abaxial side. Inflorescences one to eight per plant, patent, racemose, 2–6 cm long, long pedunculate, longer than leaf, arising from the nodes at the opposite side of the leaves, green, slightly spotted purplish red; peduncle slender, slightly upwards curved from the middle, 1.5–5 cm long, 0.4–2.0 mm diam., with 2–3 internodes, the basal internode somewhat shorter, 0.5–2.0 cm long, 0.4–0.5 mm diam., the middle internode longer, 1.5–4.0 cm long, 0.4–1.0 mm diam., the terminal internode swollen distally, 0.5–2.3 cm long, broadening to 2.0 mm diam. just below rachis; peduncle scales 2–3, green, broadly ovate to triangular, incurved, concave, thickened, slightly boat-shaped, clasping the peduncle, 1.2–2.0 × 0.8– 1.5 mm, apex acute, keeled; rachis relatively short, 0.3–1.2 cm long, depending on the age of the inflorescence, densely 4–17-flowered, with one flower open at a time, swollen, 3–6 mm diam., clearly thicker than the peduncle. Floral bracts quaquaversal, green, broadly ovate to triangular, incurved, concave, thickened, slightly boat-shaped, clasping the rachis, 1.5–2.0 × 1.0– 1.5 mm, apex acute, keeled. Pedicel-with-ovary yellowish green, cylindrical, 6-grooved, 2.5– 7.0 mm long, 1.0 mm diam. Flowers resupinate, opening widely, lasting only one day, membranaceous, 0.8–1.2 cm across, mildly sweet-scented; tepals bright yellow, lip white, spotted with brownish orange on both surfaces of the sac and at apex of the callus, the sac with orange warts inside on the back wall which shine through on the outside, column and anther white, pollinia bright yellow, stipe and viscidium creamy white. Dorsal sepal obovate to elliptic, 3.5–8.0 × 2–4 mm, concave, slightly boat-shaped, apex obtuse, glabrous, 5-nerved, nerves reticulate branching. Lateral sepals broadly ovate, subfalcate, 4–7 × 3–5 mm, obliquely dilated at the lower margin, slightly concave, with a low abaxial keel, the base broadly connected with the column-foot, obtuse, glabrous, 5-nerved, nerves reticulate branching. Petals oblanceolate, 4.4–4.5 × 1.8–2.0 mm, slightly oblique, curving downward from the middle, shorter and narrower than the sepals, slightly concave, obtuse, glabrous, 3-nerved, nerves reticulate branching. Lip suborbicular in outline when spread, 3-lobed, 5–7 × 2.0– 3.5 mm in natural position, 6–8 mm wide when spread, with a broad, sac-like spur at the base; spur oblong-conical, 2.0–2.2 × 1.5–2.5 mm, apex shallowly bilobulate with obtuse lobules (0.3 × 1 mm), inside towards the base of the callus with scattered small orange warts, and densely covered with long clavate hairs (0.5 mm long) towards the lip blade; lateral lobes obliquely obovate, distinctly surpassing the mid-lobe, 4–5 × 3 mm, with rounded apex, erect, curving forwards and bent inwards, clasping the column, adaxial surface sparsely covered with 0.5 mm long clavate hairs in the basal part and along the apical margins, abaxial surface glabrous; mid-lobe short, broadly triangular to rounded, 0.5–1.0 × 2–3 mm, somewhat concave, densely covered with 0.5 mm long clavate hairs on the adaxial surface and along the margins, rather thick (1.0– 1.5 mm), fleshy, entire, apex emarginate (each lobule 0.5 × 1.5 mm); lip adaxially between the lateral lobes sparsely covered with long clavate hairs, glabrous abaxially, a little below the mid-lobe with a trapeziform callus 1.0– 1.5 mm long, 1–2 mm diam., apex bilobulate, decurved. Column cylindrical, short, stout, 2 × 1.5–2.0 mm, laterally winged; column-foot short, broad, 1.0–2.5 × 1.5–2.5 mm. Anther suborbicular in outline, glabrous, 1.0 × 1.2 mm. Pollinia in two pairs, those in a pair unequal, elliptic, curved; the larger 0.8 × 0.5 mm; the smaller, 0.6 × 0.4 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 green, narrowly cylindrical, 70 mm long, 4 mm diam., with 6 longitudinal ridges. Described from living plants and flowers, and spirit material.

Distribution:— THAILAND. Eastern: Nakhon Ratchasima Province (Khao Yai National Park); South-Western: Uthai Thani Province (Huai Kha Khaeng Wildlife Sanctuary); Phetchaburi Province (Kaeng Krachan National Park); Prachuap Khiri Khan Province (Khan Kra Dai) ( Fig. 25 ).

Phenology:—Flowering in January, March, April and May (in natural habitat, four records); April (in cultivation, one record). Flowering is probably intermittent throughout the year, as in most species of Thrixspermum .

Habitat and ecology:—Epiphyte in dry evergreen and mixed deciduous forests, at 300–600 m elevation, locally common along streams and surrounding zones, growing on twigs of small trees, such as Lagerstroemia floribunda Jack (1820: 509) (Lythraceae) and (introduced) Psidium guajava L. ( Linnaeus 1753: 470) ( Myrtaceae ), in exposed positions at about 1–3 meters above the ground.

Conservation status:— Thrixspermum alboluteum has been recorded from four localities in Eastern Thailand from Khao Yai National Park and South-Western Thailand, namely from the Huai Kha Khaeng Wildlife Sanctuary, Kaeng Krachan National Park and Khan Kra Dai Cave, with an Extent of occurrence (EOO) of 49,773.942 km 2 and an Area of occupancy (AOO) of 16.000 km 2. Although the species occurs in a strictly protected area in Khao Yai National Park and Kaeng Krachan National Park, it has a very small known population there of less than 10 mature individuals. The natural habitat in Kaeng Krachan National Park was also destroyed by being developed into a campsite and visitor centre, and visitors also collected the plants. It is, however, possible that the new species can be found distributed in other similar habitats in both sites. Khan Kra Dai Cave is currently being developed for the local temple; it is surrounded by plantations and is becoming more popular among tourists, all of which poses a considerably threat to the population of this species. However, it seems to be fairly common in Huai Kha Khaeng Wildlife Sanctuary, with more than 1,000 mature individuals present in several places, located in a diverse forest of the wildlife sanctuary and with strict protection (Priwan Srisom and Salil Sittisatjathum, pers. comm.). It is, therefore, provisionally assigned the conservation status of Vulnerable (VU) according to IUCN criteria (Vulnerable: B1a, c; C2a; D1, 2). More insight into the distribution of this species is needed for a reliable assessment.

Etymology:—From the Latin album , white, and luteum, yellow, referring to the yellow tepals and the mainly white lip.

Vernacular ( Thailand):— ตะขาบเหลืองตะนาวศรี (Takhap Lueang Tanao Si), ตะขาบเหลืองปากหยัก (Takhap Lueang Pakyak).

Additional specimens examined:— THAILAND. Eastern: Nakhon Ratchasima Province, Pak Chong, Khao Yai National Park, Cumberlege 526 (C 8433!, K 24716!, Seidenfaden 1988: 166 as T. musciflorum ), Cumberlege 527 (C 8428!, K 27388!, Seidenfaden 1988: 166 as T. musciflorum ), Haew Suwat Waterfall, Seidenfaden & Smitinand GT 5790 (C 8353!, 8354!, Seidenfaden 1988: 162 as T. trichoglottis ); South-Western: Uthai Thani Province, Huai Kha Khaeng Wildlife Sanctuary, K.S. s.n., 03 April 1991 (BCU s.n.!), Phetchaburi Province, Kaeng Krachan National Park, S. Raksue 79, 16 April 2008 (BKF s.n.!), Prachuap Khiri Khan Province, Khan Kra Dai, Put 2318, 16 January 1929 (C 8379!; K s.n.!, Seidenfaden 1988: 166 as T. musciflorum ), A.F.G. Kerr 0736, 21 March 1929 (K s.n.!, Seidenfaden 1988: 166 as T. musciflorum ).

Taxonomic notes:— Thrixspermum alboluteum may be recognised by the combination of the obliquely obovate lateral lobes of the lip surpassing the triangular, concave and emarginate mid-lobe, the long clavate hairs on the lip, yellow flowers with a white lip, and orange warts inside the spur. It is morphologically similar to T. formosanum ( Fig. 4E–F ), a species from India , southern China, North Vietnam and Taiwan ( Lin & Hsu 1977, Chen et al. 2009, the Editorial Committee of the Flora of Taiwan 2000, Lin & Wang 2014, Gogoi & Yonzone 2015, Kaliamoorthy & Saravanan 2019, Khanal et al. 2022), because of its small stature with oblong or lanceolate to linear leaves, inflorescences longer than the leaves, and sepals and petals similarly shaped; it differs in having yellow flowers, a lip with brownish orange spots and orange warts, a distinct mid-lobe with emarginate apex, and obovate lateral lobes.

Having critically compared the original descriptions and the type specimens of T. formosanum (T. Kawakami & N. Mori s.n., Formosa, 1907, K 000891322!, type of Sarcochilus formosanus Hayata ) and T. musciflorum (Joseph 45621A, between Umran & Umsaw beside the Gauhati-Shillong highway, Nongpoh, Meghalaya, India , 23 July 1966, ASSAM 0000000209!, image seen) and the relevant literature of both species, we conclude that the two taxa are conspecific; they agree in being small plants with stems 1.5–3 cm long, white flowers 1.0– 1.2 cm across, an obovate to elliptic dorsal-sepal, ovate lateral-sepals, oblanceolate petals, a white lip, marked with pinkish to brownish stripes, triangular lateral lobes, and an indistinct mid-lobe with orangish markings and glandular hairs. In India and Bhutan, T. formosanum has often been identified as T. musciflorum ( Rao & Joseph 1969; Kataki 1986; Chowdhery 1998; Bose & Bhattacharjee 1999; Dalström et al. 2017; Misra 2019; Barbhuiya et al. 2021). We also find no significant differences between T. formosanum and T. musciflorum var. nilagiricum Joseph & Vajravelu (1981) . In contrast, the species we here describe as T. alboluteum had been misidentified as T. musciflorum by Seidenfaden 1988. His drawing, taxonomic notes and photographs (C-SEIDENFADEN no. 24-157!, 24-158!, 24-159!, 24-161!, 24-162!, 24-163!, 24-192!, 24- 193!, 24-194!) perfectly match our plant from Kaeng Krachan National Park. We also note that the species illustrated as T. musciflorum in Singh et al. (2019: 492) is T. indicum Vik.Kumar, D.Verma & A.N.Rao ( Kumar et al. 2017) .

Thrixspermum alboluteum is also similar to T. patkaiense K. Gogoi ( Gogoi 2022: 9, as ‘ patkaiensis ’), a recently described species from north-eastern India , which also occurs in central Laos ( Averyanov 2018, as T. hystrix auct. non (Blume) Rchb.f.), Myanmar (photos by H. Kurzweil seen), and Thailand (pers. obs. Nopparut Toolmal). Like T. alboluteum , T. patkaiense ( Fig. 4C–D ) has yellow tepals but it has a yellow lip marked with longitudinal purplish red stripes on both surfaces of the lateral lobes towards the spur, the mid-lobe yellowish with an orange band along the apical margins, and a callus that is distinctly raised at the apex (vs. a white lip with different markings, see description, and a nearly flat callus). In T. alboluteum the lateral lobes are obovate and broadly rounded (vs. broadly ovate), the mid-lobe is densely covered with long capitate hairs on the adaxial surface and along the margin but not abaxially (vs. covered on both surfaces). The spur of T. alboluteum differs from that of T. patkaiense in being proportionally narrower, 2.0–2.2 × 1.5–2.5 mm (vs. 2.5 × 3.0– 4.2 mm). Both species have orange warts inside the spur.

Figures

FIGURE 1. Thrixspermum alboluteum. A. Habit. B. Leaf apex. C. Flower (front view).D. Rachis with flowers. E. Column & column-foot with petal & lateral sepal (lateral view). F. Sac with warts on the backwall (close-up). G. Lip (lateral view). H. Lip (longitudinal section). I. Lip (adaxial view, natural position). J. Lip (adaxial view, spread out). K. Dissected perianth. L. Column with pedicel (ventral view). M. Operculum (dorsal view). N.Anther with pollinia, stipe & viscidium (ventral view). O. Pollinia (two pairs). P. Stipe & viscidium. (Drawn from holotype, N. Toolmal et al. 20122001, TTM 0006394). Illustration by Phattaravee Prommanut.

FIGURE 2. Thrixspermum alboluteum. A.Flower (front view).B. Flower (oblique view). C. Flower (ventral view).D. Dissected perianth. E. Tepals with column and column-foot.F. Column & column-foot with pedicel (ventral & dorsal views).G. Lip, adaxial view (left: natural position; right: spread out). H. Lip, abaxial view (left: natural position; right: spread out) with scattered orange warts. I. Lip (left: lateral view). J. Lip (showing long capitate hair on the mid-lobe). K. Anther with pollinia (left: ventral view; right: dorsal view). L. Operculum (left: ventral view; right: dorsal view). M. Stipe & viscidium. N. Pollinia (two pairs). O. Pollinia (individual). Photographed by Wattana Tanming (A–J) & Nopparut Toolmal (K–O). Illustration assembled by Yongyuth Rattanasootr. A–J from living collection (QSBG) and K–O from spirit collection of N. Toolmal et al. 20122001 TTM 0006394.

FIGURE 3. Thrixspermum alboluteum. A. Plant habit. B. Leaf (adaxial view). C. Leaf apex. D. Flower, rachis and floral bracts (ventral view). E. Flower (ventral view). Photographed by Nopparut Toolmal (A–C & E. In situ) & Wattana Tanming (D & E. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 4. A comparison of allied species. A–B. Thrixspermum alboluteum. C–D. Thrixspermum patkaiense. E–F. Thrixspermum formosanum. Photographed by Wattana Tanming (A–B. Cultivation, QSBG), Nopparut Toolmal (C–D. In situ) & Morris Ng (E–F. Cultivation, Taiwan). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 25. Distribution map of Thrixspermum alboluteum in Thailand.