Dendrobium chiangdaoense Promm., Kidyoo, Buddhawong & Suddee, 2017

Prommanut, Phattaravee, Kidyoo, Manit, Buddhawong, Wins & Suddee, Somran, 2017, Dendrobium chiangdaoense (Orchidaceae), a new species from Thailand, Phytotaxa 307 (1), pp. 84-88 : 84-87

publication ID	https://doi.org/ 10.11646/phytotaxa.307.1.8
persistent identifier	https://treatment.plazi.org/id/03BE878C-0305-4E44-6697-F907793AF8E8
treatment provided by	Felipe
scientific name	Dendrobium chiangdaoense Promm., Kidyoo, Buddhawong & Suddee
status	sp. nov.

Treatment

Dendrobium chiangdaoense Promm., Kidyoo, Buddhawong & Suddee View in CoL sp. nov. ( Figs. 1 View FIGURE 1 & 2 View FIGURE 2 )

Dendrobium chiangdaoense is most similar to D. dixonianum but differs in having bract longer than pedicel plus ovary, inflorescences not exceeding leaves, lateral sepals obliquely falcate-triangular not recurved, labellum bright green, apex of keel acute and not divided to lobes.

Type:— THAILAND. Chiang Mai Province: Chiang Dao District, road to Ban Huay Ja Khan, ca. 800 m elev., 13 October 2015, Buddhawong & Suddee 018 (holotype BKF!).

Plant epiphytic, tufted, with smooth roots. Pseudobulbs erect, fusiform or cylindric, base slightly contracted, become narrowed toward apex above middle, sulcate, light green, 0.9–2.2 cm tall, internodes 3–8 mm long, 4–6 mm in diam., fleshy, with 2–3 nodes, developing young pseudobulb enclosed by leaf sheaths; leaf sheath membraneous, glabrous on both sides, bright creamy brown, mature old pseudobulb naked, dull greenish-yellow or bright yellow. Foliage leaves 2–3, distichous, spreading, slightly recurved, linear-oblong, elliptic or oblong, 2–3 × 3–5 mm, apex unequally and shortly 2-lobed, each lobe acute, base expanded into sheaths, chartaceous, glabrous on both sides, lowermost smaller than upper, light green above, pale green or greenish-yellow beneath, mid-vein grooved above and ribbed below. Inflorescences raceme, 1–2-inflorescenced, axillary and terminal, erect, 1.3–2.5 cm long, lax, 3–5-flowered; peduncle and rachis glabrous, bright green, peduncle 6–9 mm long, rachis 2–7 mm long, covered with bracts; floral bracts pale green, slightly concave, oblong or narrow lanceolate, 4–5 × 1–1.5 mm, apex acuminate, base truncate, margin entire, 1-veined, glabrous on both sides, abaxial surface distinctly keeled, bracteoles pale green or greenish-white, narrowly lanceolate, 4–5 × 1–1.2 mm, apex acuminate, base truncate, margin entire, 1-veined, glabrous on both sides, distinctly keeled below. Flowers resupinate, waxy and polished, scented, long-lasting, 6–8 mm in diam. Sepals pale green with dull green at base, spreading, often recurved distally, margin entire, abaxial surface distinctly keeled; dorsal sepal linear-lanceolate, 6.8–7 × 1.4–1.5 mm, apex acuminate, base truncate, 3-veined, distinctly visible, mid-vein grooved above; lateral sepals obliquely falcate-triangular, 7–7.5 × 5–5.2 mm wide at base, not recurved, apex acuminate, base obliquely truncate, 3–4-viened, distinctly visible. Petals green, with 3 longitudinal light reddish-purple veins, spreading, linear-oblanceolate, 6.3–6.5 × 0.9–1 mm at middle, apex acute, base truncate, margin entire, 3-veined, distinctly visible. Labellum light green with reddish-purple dots, recurved at apex, 3-lobed, 6–6.5 × 4–4.5 mm across side lobes, attenuate at base; side lobes bright green, triangular, forwards and upwards pointed, ca. 1 × 0.4–0.5 mm, margin serrate; disc narrowly oblong, adaxial surface smooth, waxy, distinctly with greenish-white thickened keel, shining, raising at hypochile, continuing to base of mid-lobe, apex of keels acute; mid-lobe dull green with 3 light reddish-purple veins, triangular, recurved, apex acuminate, margins undulate-serrate. Mentum light green with purple dots, narrowly conical, 6–6.5 mm long, 1–1.2 mm in diam., margin and surface papillate, straight or incurved distally. Column glossy green with slight purple tinge, short, 1.9–2 × 0.9–1 mm at base, margin entire, surface colliculate; foot concave, stout at base, waxy, 1–2 × 0.9–1 mm at base; stigmatic cavity whitish-green, elliptical shaped, stelidia acute, anther cap yellowish-green, subglobose or widely obovate, 0.9–1 × 0.8–1 mm, apex emarginate, basal margin denticulate or ciliate, surface bullate, adaxial side sulcate; pollinia 4, bright yellow, in 2 pairs, each pollinium narrowly elliptic, 0.9–1 × ca. 0.5 mm, without caudicle and visidium. Ovary (including pedicel) narrowly clavate, curved, 2.3–2.5 mm long, glabrous, somewhat waxy, 6-grooved. Capsule not seen.

Distribution. — Northern Thailand (Chiang Mai Province).

Habitat & Ecology.— Epiphytic herb on tree trunks in mixed deciduous forest on limestone hills at ca. 800 m elev. Flowering from October to November.

Etymology.— The epithet “ chiangdaoense ” refers to the Chiang Dao District, the locality where the plants were found and collected.

IUCN Red List category:— Dendrobium chiangdaoense is known only from the type locality and the estimated number of mature plants is less than 10 in a single population. Furthermore, the habitat has been partially destroyed for agricultural purposes. The species is considered to be facing an extremely high risk of extinction in the wild. Following the IUCN Red List Categories and Criteria (2016), it is strongly suggested that D. chiangdaoense should be treated as a critically endangered species (CR).

Observations:— Dendrobium chiangdaoense is similar to D. dixonianum Rolfe ex Downie (1925: 373) by having labellum with distinct side lobes and adaxial surface with keel, but differs by characters shown in Table 1 & Figure 2 View FIGURE 2 . In addition, D. chiangdaoense has fusiform or cylindrical pseudobulb, 0.9–2.2 cm tall (inflorescence length not included), bract longer than pedicel plus ovary, and grows in mixed deciduous forest on limestone hills at ca. 800 m elev. On the other hand, D. dixonianum has fusiform or cylindrical pseudobulb, up to 5 cm tall, bract shorter than pedicel plus ovary, and grows in upper montane rain forest at 1,650 –1,800 m elev.