Gastrodia sabahensis J.J. Wood & A. Lamb (in Wood 2008: 39)

Type:— MALAYSIA, Sabah, Sandakan distr., Kebun China Forest Reserve, lowland mixed dipterocarp forest on sandstone, ca. 50 m alt., 28 MAY 2003 (Lamb AL 525/2003 SAN). Figs 1, 2.

Description:— Terrestrial, achlorophyllous herbs up to 7.5 cm tall. Rhizome ca. 50 mm long, 4–6 mm wide in nodes, tuberous, fleshy, with many internodes, constricted in nodes, densely covered by filiform scales. Stem basally ascending, erect, dark brown, 50–60 mm long, 1.5–2 mm in diameter, with 4–6 nodes. Leaves 4.5–5.5 mm long, 1.6 mm wide at base, scale-like, broadly triangular, dark brown, basally clasping. Bracts 2, unequal in shape and size, dark brown, shorter one 4.0 mm long, 0.5 mm wide at base, 2.5 mm wide in the middle part and 1.5 mm wide in thin apical part, stipitate ovate with tapering tip, longer one 5.0 mm long and 1.5 mm wide, broadly triangular. Inflorescence loose, 1–2 flowered. Pedicel 5.0 mm long, 1.0 mm in diam., beige to pinkish brown. Flower 15.5 mm long, 12.5 mm in diam., facing upwards, wide open, with sepals and petals basally fused for ca. 1/2 to 2/3 of their length, forming a five-lobed, widely campanulate perianth tube; flower bud dark brown with almost black tip. Sepals externally whitish brown, pale brown to medium brown, with dark brown tips, sparsely covered by low blunt processes, internally orangish brown to reddish brown at base and yellowish white to cream yellow apically. Free portion of lateral sepals 3.5 × 6.0 mm, broadly triangular, internally with white to yellowish white, cushion-like verrucose tissue, ca. 9.5 × 4.0 mm. Free portion of dorsal sepal 6.0 × 8.0 mm, broadly triangular. Free portion of petals 1.5 × 2.0 mm, widely triangular to ovate triangular, bent upwards in matured flowers, yellow to orange, with a translucent margin. Lip ca. 9.0 × 4.5 mm, adnate to base of column, adpressed to perianth tube, orange; hypochile ca. 5.0 × 4.5 mm, thick and fleshy, almost flat, broadly elliptic to orbicular; epichile 1.5 × 2.0 mm, oblong with rounded apex, yellowish white to yellow; keel 1.0– 1.5 mm wide, positioned at the transition of hypochile and epichile, whitish, with margins raised into two ridges which have the tallest part at their origin in hypochile; calli globose, yellowish orange. Column ca. 5.0 × 3.0 mm, straight, oblong, winged, central part whitish brown, wings beige, ventricose, each abruptly ending in triangular, brown to reddish brown rostellum; stelidia brown to reddish brown, terete, obtuse, equal to anther; anther cap ca. 1.0 × 1.0 mm; pollinia not seen; stigma greenish brown, trapezoid. Ovary 4.0 × 2.5 mm, obconical, slightly bent and ventricose, dark brown. Capsule not seen.

Specimens examined:— BRUNEI DARUSSALAM. Temburong distr.: Kuala Belalong, E ridge of Sungai Belalong, ca. 1.5 km SE from its confluence with Sungai Temburong, ecological plot 2, 24 JAN 2016 (Dančák 2016/157 OL!); ibidem. 30 JAN 2016 (Sochor 2016/368 BRUN!); Kuala Belalong, E ridge of Sungai Belalong, ca. 800 m SE from its confluence with Sungai Temburong, near ecological plot 1, 28 JAN 2016 (Sochor, uncollected; Fig. 2A); Kuala Belalong, E ridge of Sungai Belalong, ca. 1.5 km SE from its confluence with Sungai Temburong, small stream ravine on the trail to ecological plot 2, 2 DEC 2022 (Dančák & Hroneš, uncollected; Fig. 2B).

Distribution:— Gastrodia sabahensis is endemic to Borneo and it occurs in Sabah and Brunei Darussalam (Fig. 3). The report of its occurrence from the Philippines by Pelser et al. (2018) is here considered erroneous (see Discussion). In Brunei Darussalam, it is currently observed only from three closely located populations in the Temburong district of Brunei Darussalam where it grows on the ridge above the confluence of Temburong and Belalong rivers.

Habitat and ecology:— Gastrodia sabahensis occurs in pristine lowland mixed dipterocarp forest. All observed populations grow on moderate, shady and quite humid slopes above small streams. Several other mycoheterotrophic species were also observed growing in their vicinity (cf. DančÁk et al. 2017, Sochor et al. 2017)., e.g., Epirixanthes elongata Blume (1823: 82), Gymnosiphon sp., Thismia inconspicua Sochor & DančÁk in Sochor et al. (2017: 264) and Tropidia saprophytica J.J. Smith (1927: 27).

Conservation status:— Wood (2008) reported G. sabahensis from three populations in Sandakan Peninsula, Sabah. Current report of the species from Brunei Darussalam raises the total number of subpopulations to six. The extent of occurrence (EOO) is calculated as 1,115 km 2 and the area of occupancy ca. 16 km 2. Populations in Brunei Darussalam are located in the Ulu Temburong National Park. These three subpopulations in Brunei Darussalam are all located on the same ridge in close vicinity to each other, and hence, in a single threatening event, there is a high probability of all these subpopulations getting affected simultaneously. Populations in Sabah occur in Kebun Cina Forest Reserve (type locality), Kabili Sepilok Forest Reserve, and in an unprotected area near Ulu Dusun village. In this unprotected area, there is an inferred decline in the quality of habitat as a result of urbanisation, and forest conversion to oil palm plantation. Accordingly, these known six sites are considered as four locations following guidelines by the IUCN Standards and Petitions Committee (2022) and the species is assessed as Endangered [EN B1ab(iii) + B2ab(iii)].