Thrixspermum polystictum 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 : 254-260

publication ID	https://doi.org/ 10.11646/phytotaxa.601.3.3
DOI	https://doi.org/10.5281/zenodo.8148388
persistent identifier	https://treatment.plazi.org/id/D62787BA-206C-FF8B-2C95-106AFCA247C6
treatment provided by	Plazi
scientific name	Thrixspermum polystictum Toolmal, Schuit. & Suddee
status	sp. nov.

Treatment

6. Thrixspermum polystictum Toolmal, Schuit. & Suddee , spec. nov.

( Figs. 21–23 View FIGURE 21 View FIGURE 22 View FIGURE 23 , 24A–B View FIGURE 24 ).

Type:— THAILAND. Eastern Thailand, Nakhon Ratchasima Province, Pakchong District , Khao Yai National Park , 10 September 2021, N. Toolmal & W. Tanming 10092102 (holotype: TTM-Spirit; isotypes: BKF, QBG) .

Thrixspermum centipeda View in CoL auct. non Lour.: Seidenfaden (1988: 152).

Thrixspermum polystictum is distingished from T. latisaccatum J.J.Sm. ( Smith 1920: 111) by the smaller flowers 5–6 cm across (vs. 8 cm across), the white lip, with reddish brown spots on the lip between the lateral lobes and on the callus (vs. yellow lip, suffused with reddish brown on the lip between the lateral lobes, without spots on the callus), the shorter and smaller sepals 26–32 × 2.6–3.0 mm, 5-nerved (vs. 38–43 × 3–5 mm, 7-nerved), the shorter and smaller petals 26–30 × 1.8–2.0 mm (vs. 35–40 × 2.0– 2.5 mm), the shorter and smaller spur 2–3 × 2–3 mm (vs. 3–4 × 4–5 mm), the shorter and smaller lateral lobes 5.7–6.0 × 2.4–3.0 mm (vs. 7 × 5 mm), the ovate mid-lobe 5 × 3.4 mm, depressed in the basal 3.2 mm, convex in apical 2 mm (vs. cylindrical mid-lobe 7 × 4 mm, depressed in the basal 2 mm, convex in apical 5 mm).

Epiphytic herb. Stems patent or subscandent, 12 cm to at least 20 cm long, with c. 11 internodes, cylindrical, slightly laterally compressed, curved upwards from the middle, covered with the leaf sheaths, 9–12-leaved; internodes 8–14 × 4.2–5.8 mm. Roots cylindrical, thick, elongate, 10 cm to at least 50 cm long, 1.2–2.8 mm diam., arising from the basal part of the stem and from nodes at the lowest leaf, not or sparsely branching. Leaves green, patent, oblong, 8–10 × 2.2–2.5 cm, sessile, slightly narrowed towards the base, leaves on the same side of the stem 2.0– 2.5 cm apart, dorsiventrally flattened, apex 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 five to nine per plant, patent, racemose, 8–9 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, 4–6 cm long, 1.5–4.5 mm diam., with 3 internodes, the basal internode fairly short, stout, 3–5 mm long, 1.8–2.0 mm diam., the middle internode longer, 4–5 cm long, 1.5–2.7 mm diam., the terminal internode strongly bilaterally compressed distally, 1.0– 1.5 cm long, broadening to 4–4.5 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, 5–6 × 2– 2 mm, apex acuminate, keeled; rachis 2.5–3.0 cm long, depending on the age of the inflorescence, 9–10-flowered, with one or two flowers open at a time, strongly bilaterally flattened, with distichous, persistent floral bracts, 1.5–2.0 mm apart, 8–10 mm wide across the floral bracts. Floral bracts green, bilaterally flattened, ovate to broadly triangular, incurved, concave, thickened, slightly boat-shaped, clasping the rachis, 8–10 × 3.0– 3.4 mm, apex acuminate, keeled. Pedicel-with-ovary yellowish green, cylindrical, 6-grooved, 9 mm long, 1.2 mm diam. Flowers resupinate, opening widely, lasting only one day, membranaceous, 5–6 cm across, mildly sweet-scented; tepals pale yellow, slightly tinged with purplish red at the base, lip white, with purplish red spots on the sac and the lateral lobes on both surfaces, with reddish brown spots between the lateral lobes on both surfaces, the spur with 1 mm diam. orangish rounded warts on the back wall which shine through on the outside, the midlobe white, the callus white with purplish red spots at the base and reddish brown spots at apex, column and column-foot creamy white tinged with purplish red, anther, stipe and viscidium creamy white. Sepals recurved at the base. Dorsal sepal linear, 26–32 × 2.6–3.0 mm, slightly tapering towards the apex, slightly concave, somewhat twisted near the base, apex acuminate, glabrous, 5-nerved, nerves reticulate branching. Lateral sepals linear, obliquely subhorizontal, 28–32 × 2.8–3.5 mm, slightly tapering towards the apex, rather concave, somewhat twisted and expanded near base, apex acuminate, glabrous, 5-nerved, nerves reticulate branching. Petals similar to sepals, slightly smaller, obliquely, 26–30 × 1.8–2.0 mm, recurved from the base, apex acuminate, glabrous, 5-nerved, nerves reticulate branching. Lip oblong to broadly ovate in outline, 3-lobed, c. 10 × 3.0– 3.5 mm in natural position, 7 mm wide when spread, with a broad, sac-like spur at the base; spur broadly conical, 2–3 × 2–3 mm, apex 3-lobed with shallowly obtuse lobes (0.5 × 0.5 mm), on the back wall densely covered with long hairs (0.5 mm long) towards the base of the callus; lateral lobes narrowly triangular to slightly ovate, subfalcate, 5.7–6.0 × 2.4–3.0 mm, free part 1.3 mm long, erect, curving outwards, shortly pubescent on both surfaces, apex obtuse; mid-lobe ovate, 5 × 3.4 mm, depressed in basal part 3.2 mm, densely pubescent on both surfaces, convex and pubescent in apical 2 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 1.5 mm long, 1.3 mm diam., glabrous, apex obtuse, decurved. Column cylindrical, short, stout, 1.3 × 1.5 mm, laterally winged; column-foot short, broad, 1.8 × 1.8 mm. Anther suborbicular in outline, glabrous, 1.5 × 1.5 mm, the median with a longitudinal ridge. Pollinia in 2 pairs, those in a pair unequal, elliptic, 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 not seen ( Figs. 20–22 View FIGURE 20 View FIGURE 21 View FIGURE 22 ). Described from living plants and flowers, and spirit material.

Distribution:— THAILAND. Eastern: Nakhon Ratchasima Province, Pakchong District, Khao Yai National Park ( Fig. 27 View FIGURE 27 ).

Etymology:—From the Latinised Greek polystictus, with many dots, referring to the markings on the lip.

Phenology:—Flowering in July and September (in natural habitat, two records); February (in cultivation, one record). Flowering is probably intermittent throughout the year, as in most species of Thrixspermum .

Habitat and ecology:—Epiphyte in dry evergreen forest at 750 m elevation, growing on twigs of small trees, (introduced) Psidium guajava L. ( Myrtaceae ), in exposed positions at about 1 metre above the ground.

Conservation status:— Thrixspermum polystictum is currently only known from the type locality in eastern Thailand. Its population size has yet to be estimated and its wider distribution remains unknown. This species could be restricted to only one national park or may be distributed in neighbouring protected areas as well. It is, therefore, provisionally assessed as Data Deficient (DD) according to IUCN criteria.

Vernacular ( Thailand):—Maeng Mum Lueang Pakkra (แมงมุมเหลืองปากกระ), Ta Khap Lueang Pakkra (ตะขาบเหลืองปากกระ).

Additional specimens examined:— THAILAND. Eastern: Nakhon Ratchasima Province, Pakchong District, Khao Yai National Park, S. Kaitongsuk 593, 29 September 2020 (BKF 01–00547!), S. Kaitongsuk 689, 06 July 2021 (BKF s.n.!), Seidenfaden & Smitinand GT 4396, October 1962 (C 8340!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 5761, 02 September 1966 (C 8303!, Seidenfaden 1988: 152 as T. centipeda ), Seidenfaden & Smitinand GT 5764B, 16 July 1968 (C 8343!, Seidenfaden 1988: 152 as T. centipeda ), Beusekom, CF van & Charoenphol, C 1813, 21 October 1969 (L 1540359!).

Taxonomic notes:—Although it has been confused with Thrixspermum centipeda , the species most similar to T. polystictum is probably the West Malesian T. latisaccatum ( Fig. 23C–D View FIGURE 23 ), as they share linear, pale yellow tepals, sepals and petals recurved from the base, and a cylindrical midlobe. Thrixspermum polystictum differs in the characters mentioned in the diagnosis, in particular in the white lip with reddish brown spots, shorter and smaller tepals, and the ovate mid-lobe with the apical 2 mm convex.

Because of the convex midlobe, T. polystictum is also similar to T. simile . It differs in having a white lip with numerous fine reddish brown spots, the callus with purplish red and reddish brown spots (vs. a pale yellow lip, adaxially marked with large, irregular, purplish red or brownish orange blotches on the sac towards the base of the mid-lobe, without spots on the callus). In Thrixspermum polystictum , the sepals are recurved, 26–32 × 2.6–3.5 mm, petals 26–30 × 1.8–2.0 mm, whereas the sepals are incurved, 26 × 3.0– 3.5 mm, petals 23–24 × 2.0– 2.5 mm in Thrixspermum simile . In Thrixspermum polystictum , the lip is 10 mm long (vs. lip 8.0– 8.5 mm long), spur 3-lobed at apex (vs. spur obtuse at apex), lateral lobes 5.7–6.0 × 2.4–3.0 mm (vs. lateral lobes 5.0–5.2 × 2.0– 2.2 mm), mid-lobe narrowly ovate 5 × 3.4 mm, depressed in the basal 3.2 mm, convex in apical 2 mm, without lateral swellings between the basal and apical parts (vs. mid-lobe broadly ovate, 3–5 × 3.5–4.5 mm, depressed in the basal 1.5–2.2 mm, convex in apical 4 mm, with lateral swellings between the basal and apical parts).