Thrixspermum simile Toolmal, Schuit. & Utteridge, 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 : 242-248

4. Thrixspermum simile Toolmal, Schuit. & Utteridge , spec. nov.

( Figs. 13–15 , 16A–B , 24E–F ).

Type:— THAILAND. South-Eastern Thailand, Chanthaburi Province, Khlung District , Mangosteen orchard in front of Trok Nong Waterfall , 24 August 2021, N. Toolmal & W. Tanming 24082101 (holotype: TTM-Spirit; isotypes: BKF, QBG) .

Thrixspermum centipeda auct. non Lour.: Seidenfaden (1988: 152) Fig. 92.

Thrixspermum simile is similar to T. lampongense J.J.Sm. ( Smith 1917: 89) in the largely convex mid-lobe of the lip but differs in the shorter, 7-veined sepals, 26 mm long (vs. 5-veined, 32–40 mm long), the shorter petals, 23–24 mm long (vs. 30–33 mm long), an oblong to broadly ovate lip 8.0– 8.5 mm long (vs. oblong 11–13 mm long), the shorter spur 2.0– 2.5 mm long (vs. 2.5–4.0 mm long), the narrowly triangular to ovate lateral lobes 5.0–5.2 × 2.0– 2.2 mm, acute to narrowly obtuse at apex (vs. narrowly triangular lateral lobes 6–9 × 3–4 mm, truncate and bilobed at apex), the ovate mid-lobe 3–5 mm long, depressed in the basal 1.5–2 mm, the convex apical part 4 mm long and 2.5 mm thick (vs. mid-lobe narrowly triangular to cylindrical 8 mm long, depressed in the basal 2–3 mm, the convex apical part 6 mm long and 3.5 mm thick).

Epiphytic herb. Stems patent, elongated or subscandent, 20 cm to at least 28 cm long, with 16–26 internodes, cylindrical, slightly laterally compressed, curved upwards from the middle, covered with the leaf sheaths, 9–18-leaved; internodes 5–16 × 2.0– 6.7 mm. Roots cylindrical, thick, elongate, 8 cm to at least 35 cm long, 0.2–3.4 mm diam., arising from the basal part of the stem and from nodes at the lowest leaf, not or sparsely branching. Leaves green, slightly spotted or suffused with purplish red, patent, oblong, 4–15 × 1.5–2.5 cm, sessile, slightly narrowed towards the base, leaves on the same side of the stem 2–3 cm apart, dorsiventrally flattened, apex slightly unequal bilobed with obtuse lobes, with a small mucro in the middle, thick, rigid, fleshy, coriaceous, the midrib distinct on the abaxial side; leaf sheaths green, slightly spotted or suffused with purplish red, slightly bilaterally compressed, longer than the stem internodes. Inflorescences eight to eighteen per plant, patent, racemose, 7–22 cm long, long pedunculate, arising from the nodes at the opposite side of the leaves and below the roots, sometime bearing two inflorescences at the same point, green with purplish red spots; peduncle slender, slightly upwards curved from the middle, 5–14 cm long 1.6–6.0 mm diam., with 3 internodes, the basal internode fairly short, stout, 0.3–2.0 cm long, 2–3 mm diam., the middle internode longer, 1–8 cm long, 1.6–2.3 mm diam., the terminal internode strongly bilaterally compressed distally, 2–4 cm long, broadening to 6 mm diam. just below rachis; peduncle scales 3, green with purplish red spots, ovate to broadly triangular, incurved, concave, thickened, slightly boat-shaped, clasping the peduncle, 5.5–7.4 × 2.2 mm, apex acuminate, keeled; rachis 2.5–12.0 cm long, depending on the age of the inflorescence, 7–29-flowered, with one or two flowers open at a time, strongly bilaterally flattened, with distichous, persistent floral bracts, 1–3 mm apart, 1.0– 1.2 cm wide across the floral bracts. Floral bracts yellowish green, bilaterally flattened, ovate to broadly triangular, incurved, concave, thickened, slightly boat-shaped, clasping the rachis, 7.5–9.0 × 2.7–2.8 mm, apex acute, keeled. Pedicel-with-ovary yellowish green, cylindrical, 6-grooved, 7 mm long, 1 mm diam. Flowers resupinate, opening widely, lasting only one day, membranaceous, 3.5 cm across, mildly sweet-scented; tepals pale yellow, lip pale yellow with creamy white mid-lobe, abaxially tinged with purplish red at the basal part of the lateral lobes and brownish orange between the lateral lobes, adaxially marked with large, irregular, purplish red or brownish orange blotches on the sac towards the base of the mid-lobe, the spur with 2 mm diam. orangish rounded warts on the back wall which shine through on the outside, callus, anther, column-foot, stipe and viscidium creamy white, column creamy white with purplish red spots. Sepals incurved at the base. Dorsal sepal linear, 26 × 3.0– 3.5 mm, slightly tapering towards the apex, slightly concave, somewhat twisted near the base, apex acuminate, glabrous, 7-nerved. Lateral sepals linear, obliquely subhorizontal, 26 × 3.5 mm, slightly tapering towards the apex, rather concave, somewhat twisted and expanded near base, apex acuminate, glabrous, 7-nerved. Petals similar to sepals, slightly smaller, obliquely, 23–24 × 2.0– 2.5 mm, apex acuminate, glabrous, 5-nerved. Lip oblong to broadly ovate in outline, 3-lobed, 8.0–8.5 × 3.0–4.0 mm in natural position, 8 mm wide when spread, with a broad, sac-like spur at the base; spur broadly conical, 2.0–2.5 × 3.0– 3.2 mm, apex obtuse, on the back wall towards the base of callus densely covered with long simple hairs (0.5 mm long); lateral lobes narrowly triangular to ovate, slightly falcate, 5.0–5.2 × 2.0– 2.2 mm, free part 1.8 mm long, erect, curving outwards, apical margins with shortly pubescent, adaxial surface glabrous, abaxial surface sometimes sparsely pubescent, apex acute to slightly obtuse; mid-lobe ovate, 3–5 × 3.5–4.4 mm, with lateral swellings between the basal and apical parts, depressed in basal 1.5–2 mm, sparsely pubescent on both surfaces, convex, pubescent in apical 4 mm, 2.5 mm thick, more or less evenly thick from base to apex, apex obtuse; lip between the lateral lobes sparsely pubescent on both surfaces, with a tongue-shaped callus a little below the mid-lobe, callus 2 mm long, 1 mm diam., glabrous, apex bilobed, decurved. Column cylindrical, short, stout, 1.5 × 1 mm, laterally winged; column-foot short, broad, 2 × 2 mm. Anther suborbicular in outline, glabrous, 1.2 × 1.5 mm, the median with a longitudinal ridge. Pollinia in 2 pairs, those in a pair unequal, lanceolate-ellipsoid, curved; the larger 1.0 × 0.5 mm; the smaller 0.8 × 0.3 mm; stipe broadly ovate-elliptic, 0.5× 0.5 mm, concave in the median, slightly translucent; viscidium transverse-linear, 0.2 × 0.6 mm, bent into a crescent shape, slightly translucent. Fruit green, cylindrical, 6–7 cm long, 6.0– 8.7 mm diam., with 6 longitudinal ridges. Described from living plants and flowers, and spirit material.

Distribution:— THAILAND. South-Western: Prachuap Khiri Khan Province (Namtok Huai Yang National Park); South-Eastern: Chon Buri Province (Sriracha), Chanthaburi Province (Namtok Phlio National Park, Trok Nong Waterfall, Makham to Soidao Districts), Trat Province (Khao Saming District, Saphan Hin Waterfall, Koh Chang, Khao Kuap); Peninsular: Phangnga Province (Bangto). CAMBODIA. Koh Kong Province and Mondulkiri Province ( Fig. 27 ).

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

Habitat and ecology:—Epiphyte in moist evergreen forest and surrounding plantations, at 50–490 m elevation, locally common along streams, waterfalls, and in the surrounding zone. Due to the frequent proximity of natural sites to orchards, it is often seen growing on trunks or twigs of Garcinia mangostana L. ( Linnaeus 1753: 443) ( Clusiaceae ), in exposed positions at about 1–3 meters above the ground.

Conservation status:— Thrixspermum simile is another widespread but overlooked species, distributed from Northern Peninsular, South-Western, South-Eastern Thailand to Cambodia, with an Extent of occurrence (EOO) of 201,917.725 km 2 and an Area of occupancy (AOO) of 48.000 km 2. Although in Thailand the species occurs in a small area, which has long been threatened by deforestation to increase the plantation areas, it apparently has a high dispersal capacity to maintain its population. It is very common locally, abundantly growing on trees in protected sites as well as the surrounding plantations. Like several other Thrixspermum species, it seems to easily colonise fruit trees (planted as well as naturalised ones), which makes it less dependent on old-growth forest than most epiphytic orchids. It is, therefore, assigned the conservation status of Least Concern (LC) according to IUCN criteria.

Etymology:—From the Latin similis, similar, referring to the superficial similarity to T. lampongense and T. centipeda , with which this species has been confused.

Vernacular ( Thailand):—Maeng Mum Lueang Pakna (แมงมุมเหลืองปากหนา), Ta Khap Lueang Pakna (ตะขาบเหลืองปากหนา).

Additional specimens examined:— THAILAND. South-Western: Prachuap Khiri Khan Province, Namtok Huai Yang National Park, Put 3176, 02 October 1930 (BK 256109!, C s.n.!, K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), K. Larsen, T. Smitinand & E. Warncke 1508, 12 August 1966 (AAU s.n.!); South-Eastern: Chon Buri Province, Sriracha, D.J. Collins 1093 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Chanthaburi Province, Namtok Phlio National Park, foothills of Khao Sabab, Seidenfaden & Smitinand GT 1672, 28 February 1961 (C 8339!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 1662 (C 8308!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 1644 (C 8287!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 1736, 29 May 1961 (C 8292!, Seidenfaden 1988: 152 as T. centipeda ), Makham to Soidao, Seidenfaden & Smitinand GT 1502, 18 February 1959 (C 8295!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 1447, 16 May 1960 (C 8305!, Seidenfaden 1988: 152 as T. centipeda ), Trat Province, Khao Saming District, Noe s.n., 31 March 1925 (BK 256110!, K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Put 2923, 24 January 1927 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Muang District, Saphan Hin Waterfall, R. Geesink, T. Hattink, C. Phengklai 6489, 03 May 1974 (C s.n.!, K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Koh Chang, Seidenfaden & Smitinand GT 3538, 07 July 1960 (C 8340!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 3638, April 1959 (C 8321!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 3639, 13 October 1959 (C 8298!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 3530, 28 February 1961 (C 8329!, Seidenfaden 1988: 152 as T. centipeda ), Koh Chang, Klong Mayom, Seidenfaden & Smitinand GT 5644, 02 April 1959 (C 8341!, Seidenfaden 1988: 152 as T. centipeda ), A.F.G. Kerr s.n., 02 April 1924 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Khao Kuap, A.F.G. Kerr 0853, 30 June 1930 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ), Put 2923, 20 May 1930 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ); Peninsular: Phangnga Province, Bangto, A.F.G. Kerr 0707, 20 February 1919 (K s.n.!, Seidenfaden 1988: 152 as T. centipeda ). CAMBODIA. Koh Kong Province, Kew cult. 2013-1591 (leg. Schuiteman, Ryan & Nut); Mondulkiri Province (photos by A. Schuiteman!).

Taxonomic notes:— Thrixspermum simile is most similar to Thrixspermum lampongense ( Fig. 16C–D ), from which it differs in the characters mentioned in the diagnosis, in particular, by having shorter sepals and petals, a broadly ovate lip, acute to narrowly obtuse lateral lobes, and a shorter, ovate mid-lobe with only the basal 1.5–2 mm concave.

Because of the yellow flowers and the linear, apically tapering tepals, Thrixspermum simile also resembles T. centipeda ( Figs. 16E–F , 19 ), the first-described species in this alliance and currently the default name for anything looking similar among continental Asian Thrixspermum species. Thrixspermum simile can be distinguished by the longer inflorescences 7–22 cm long (vs. inflorescences 3–6 cm long), the smaller flowers 3.5 cm across (vs. flowers 5–5.5 cm across), the shorter spur 2.0– 2.5 mm (vs. spur 7–8 mm), the longer lateral lobes 5.0– 5.2 mm (vs. lateral lobes 2 mm), the mid-lobe ovate 3–5 × 3.5–4.4 mm, depressed only in the basal 1.5–2 mm, convex in apical 4 mm (vs. mid-lobe triangular, 6 × 2.5 mm, concave throughout).

Compared with Thrixspermum species from Malesia, T. simile is most similar to T. celebicum Schltr. (Schlechter 1911: 205) , as they share linear (tapering), 23–26 mm long and yellow tepals with pale yellow to yellow lips, tinged or spotted with reddish to brownish orange on the lip between the lateral lobes, but it can be distinguished by the lip mid-lobe being concave only in the basal 1.5–2 mm, sparsely pubescent, convex in apical 4 mm (vs. mid-lobe concave from base to apex, pilose) and the apically pubescent side lobes with entire margins (vs. side lobes ciliate with erose margins).

Thrixspermum simile also resembles three Thrixspermum species from New Guinea, T. platystachys (F.M.Bailey) Schltr. (Schlechter 1911: 55) , T. collinum Schltr. (Schlechter 1913: 959) , and T. validum J.J.Sm. (Smith 1908: 37) , because of their linear (tapering) and yellow tepals, however, it has shorter tepals 23–26 mm long, a shorter lip 8.0– 8.5 mm long, an ovate mid-lobe, pubescent, and convex in apical 4 mm, whereas in the three New Guinea species the tepals are 35–38 mm long, the lip is 17–18 mm long, the mid-lobe triangular, glabrous or papillose, and with a median concavity throughout.

Figures

FIGURE 13. Thrixspermum simile. A. Habit. B. Rachis with flowers (front view). C. Rachis with flowers (lateral view). D. Lip (natural position, adaxial view). E. Dissected perianth. F. Lip with column, column-foot & pedicel (lateral view). G. Lip (adaxial view, spread out). H. Lip (longitudinal section). I. Column with pedicel (ventral view). J. Operculum (dorsal view). K. Pollinia (two pairs). L. Stipe & viscidium. (Drawn from holotype, N. Toolmal et al. 24082101, TTM 0006416). Illustration by Phattaravee Prommanut.

FIGURE 14. Thrixspermum simile. A. Flower (front view, close-up). B. Dissected perianth. C. Lip with column, column-foot & pedicel (lateral view). D. Lip, adaxial view (left: natural position; right: spread out with large orange warts on the back wall of spur). E. Lip (left: longitudinal dissection; right: lateral view). F. Column & column-foot with pedicel (ventral, lateral & dorsal views). G. Operculum (left: dorsal view; right: ventral view). H. Pollinia (left: two pairs; right: individual). I. Stipe & viscidium. Photographed by Nopparut Toolmal (A & G–I) & Wattana Tanming (B–F). Illustration assembled by Yongyuth Rattanasootr. A–F from living collection and G–I from spirit collection (QSBG) of N.Toolmal et al. 24082101 TTM 0006416.

FIGURE 15. Thrixspermum simile.A. Plant habit. B. Inflorescences with flowers. C. Rachis with flowers (front view). D. Flower (oblique view, close-up). E. Flower (lateral view, close-up). Photographed by André Schuiteman (A–B. In situ, Mondulkiri Province, Cambodia; D. In situ, Koh Kong Province, Cambodia) & Wattana Tanming (C & E. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 16. A comparison of allied species. A–B. Thrixspermum simile. C–D. T. lampongense. E–F. T. centipeda. Photographed by Wattana Tanming (A–B. Cultivation, QSBG), Nopparut Toolmal (C–D. Cultivation, QSBG) & Pilchar Ngai (E–F, Cultivation, Hong Kong). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 19. Thrixspermum flammeum. A–B. Plant habit. C. Inflorescences with flowers. D–E. Flower (ventral view). F. Flower (lateral view). Photographed by André Schuiteman (A. In situ, Champasak, Laos), Chaiwat Tunkpradit (B. In situ, Thailand), Wattana Tanming (C–E. Cultivation, QSBG) & Nopparut Toolmal (F. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 24. A comparison of allied species. A–B. Thrixspermum polystictum. C–D. T. latisaccatum. E–F. Thrixspermum simile. Photographed by Wattana Tanming (A–F. Cultivation, QSBG). Illustration assembled by Yongyuth Rattanasootr.

FIGURE 27. Distribution map of Thrixspermum simile and T. polystictum in Thailand and Cambodia. It could represent a different taxon.