A new orchid species, Gastrodia microchila is described and illustrated. The species was found in a mixed dipterocarp forest in the Belait district, Brunei Darussalam, northern Borneo in 2024. It is distinct from most Gastrodia species in western Malesia by its small lip and column, and presence of the smooth cushion-like tissue on the inner side of lateral sepals. Gastrodia microchila is only the second species of Gastrodia recorded for Brunei Darussalam and the seventh known species for Borneo. A determination key for all Gastrodia species occurring in western Malesia is also provided.

Borneo, endemic species, holomycotrophic orchid, Malesia, mycoheterotrophy, tribe Gastrodieae

The mycoheterotrophic flora of north-western Borneo (Sarawak and Brunei Darussalam) is exceptionally rich, including more than twenty species of Thismia (Thismiaceae), five species of Epirixanthes (Polygalaceae) and eleven species of Sciaphila (Triuridaceae) (Dančák et al. 2017; Dančák et al. 2020a, 2020b). The reported occurrence of only two species of Gastrodia, one from Sarawak and one from Brunei Darussalam (Wood et al. 2011; Hroneš et al. 2024), is thus in stark contrast with the diversity of other mycoheterotrophs and, more notably, with the six reported Gastrodia species from neighbouring Sabah (Wood et al. 2011). The more so, considering that Gastrodia is the second most species-rich genus of mycoheterotrophic plants globally (POWO 2024).

The genus, if treated in the wide sense, comprises 107 species (Khanal et al. 2024a, 2024b; POWO 2024; Qin et al. 2024; Chowlu et al. 2025) distributed from tropical western Africa and Madagascar, throughout southern and southeastern Asia, to Japan and eastern Siberia, eastern Australia, New Zealand and Pacific islands (POWO 2024). A comprehensive genus-wide taxonomic revision and phylogeny of Gastrodia is still lacking. The most recent infrageneric taxonomy proposed by Schlechter (1911), who recognised sections Eu-Gastrodia, Codonanthus and Strogadia, is not sufficient as it does not reflect known morphological diversity in the genus. However, an attempt to divide the genus into four separate genera Demorchis, Leptogastrodia, Neoclemensia and Gastrodia s. str. by Clements and Jones (2019) was also not widely accepted (Schuiteman 2021; POWO 2024). The rapidly increasing number of described species therefore requires a deeper focus on the evolution of the genus and the recognition of natural groups.

Species of Gastrodia are achlorophyllous, mycoheterotrophic herbs with reduced vegetative organs and fleshy tuberous rhizomes (Pridgeon et al. 2005; Ong 2015). Tubers of G. elata Blume are used in traditional medicine (Zhan et al. 2016). The flowers are resupinate to double resupinate, with three sepals and two petals connate into campanulate to tubular synsepalum inside which the lip and column are positioned (Pridgeon et al. 2005; Ong 2015). Many species are probably pollinated by small flies and display typical myophily pollination syndrome, i.e., white or brown-coloured flowers which emit a rotting fruit-like odour (Carr 1928; Martos et al. 2015). The flowers of some species are ephemeral, flowering for only a few days (Carr 1928, 1929). Due to their cryptic colours and short flowering period, many Gastrodia species are inconspicuous and easily overlooked in the field, which may explain why they are understudied in some areas such as Borneo (cf. Wong 2023).

In total, the occurrence of sixteen species is reported from western Malesia. Of these, only Gastrodia javanica (Blume) Lindl. is widespread, G. bambu Metusala occurs in Java and Vietnam, G. effusa P.T. Ong & P. O’Byrne in Borneo and Malay Peninsula, G. exilis Hook.f. in southern India, Assam, Thailand, Cambodia and Sumatra, G. spathulata (Carr) J.J. Wood in Borneo and Java and G. verrucosa Blume in Java, Sumatra and Thailand (Ong and O’Byrne 2012; Metusala and Supriatna 2017; Suetsugu et al. 2017; Suetsugu et al. 2018a; POWO 2024). The remaining species are endemic to the respective island or peninsula, i.e. Borneo (3 species), Java (4 species), the Malay Peninsula (2 species) and Sumatra (1 species). In Borneo, the species diversity is concentrated in Sabah, with the presence of all six species reported from the island: G. effusa, G. grandilabris Carr, G. javanica, G. maliauensis Suetsugu, M. Suleiman & Tsukaya, G. sabahensis Wood & Lamb, and G. spathulata (Wood 2008; Wood et al. 2011; Suetsugu et al. 2018b). Gastrodia javanica occurs also in Sarawak and G. sabahensis has recently been recorded from Brunei Darussalam (Wood et al. 2011; Hroneš et al. 2024). No species is known from Kalimantan. New discoveries are therefore likely.

During our ongoing research on mycoheterotrophic plants of Brunei Darussalam, we found a second species of Gastrodia for the country which did not resemble any species reported from Borneo. After a thorough examination of its morphology, it is described here as a new species.

This study is based on the material collected in November 2024 in a forest on the northern slopes of Telingan Hill (Belait district), Brunei Darussalam. Morphological characters were studied on living plants and documented by macro photography. Morphological characters were compared with the protologues and relevant floristic literature of Gastrodia species from western Malesia, i.e. Borneo, Java, Peninsular Malaysia and Sumatra (Blume 1825, 1856; Smith 1903, 1921, 1931; Carr 1929, 1935; Wood 2008; Wood et al. 2011; Ong and O’Byrne 2012; Ong 2015; Tsukaya and Hidayat 2016; Metusala and Supriatna 2017; Suetsugu et al. 2018b; Schuiteman 2021). A voucher specimen has been deposited in BRUN (Thiers 2025). The morphological description was prepared from several individuals, but several floral characteristics (morphology of calli and column) are based on a single flower. Morphological description follows the terminology given in Ong (2015) and the level of information presented in Hroneš et al. (2024). The preliminary conservation assessments are based on the most recent version of the guidelines of the IUCN Standards and Petitions Committee (2024).

The discovery of G. microchila represents the second known species of the genus in Brunei Darussalam (Hroneš et al. 2024). It is a valuable addition to the already rich mycoheterotrophic flora of northwestern Borneo and indicates that, despite the current progress, little is known about the actual diversity of these elusive plants.

The most (and only) similar species to G. microchila in western Malesia is G. holttumii from Peninsular Malaysia (Carr 1929; Ong 2015). Both species have lateral sepals internally with cushion-like smooth tissue covering most of the sepal space and very similar size and shape of lip and column but differ in dimension, shape and colour of several traits, especially the floral ones (see also Diagnosis). Unfortunately, the holotype of G. holttumii in SING contains only a fruiting plant, the flowers have not been preserved to the present (Ong 2015). Therefore, Ong (2015) selected a well-preserved flowering plant as an epitype which slightly differs in flower size and the shape of lip and column from the original description. Overall, G. microchila is more similar to the original description of G. holttumii (Carr 1929). Gastrodia holttumii has relatively short and thick, “potato-like” tubers interrupted by very thin internodes, while G. microchila has long and relatively slender cylindrical tuber without distinct interruptions. The flowers of G. holttumii are 5–7 mm longer and ca. 2 mm wider than those of G. microchila. The colour of G. holttumii flowers differs between the original description and the epitype. It is described as pale yellow-brown (Carr 1929) or orange-brown with darker tips (Ong 2015), while it is pale pinkish orange in G. microchila. The lip colour in G. microchila is richer than in G. holttumii. Fruiting pedicel elongates in G. holttumii to 40 cm which is the longest in any Gastrodia from the Malay Peninsula (Carr 1929; Ong 2015). The pedicel elongation in G. microchila is quite variable, spanning 1–10 cm but does not reach the length observed in G. holttumii.

Due to its tubular-campanulate flowers covered by low blunt verrucae, G. microchila is also superficially similar to several Gastrodia species from western Malesia, especially G. abscondita J.J.Sm., G. bambu, G. crispa J.J.Sm., G. maliauensis, G. selabintanensis Tsukaya & A.Hidayat, and G. verrucosa. However, it differs from them by its very small lip and column which both are only ca. 3.0 mm long (vs. 4.0–12.0 mm long lip and 5.5–12.0 mm long column in the rest of the species). Gastrodia microchila also has very short petals when compared to other species. Its petals are less than 1 mm long, almost indistinct in some flowers. Another distinct morphological trait of G. microchila is the smooth cushion-like tissue located on the inner side of lateral sepals. To the best of our knowledge, this tissue is absent in the above-mentioned species, but we cannot rule out the possibility that it was overlooked, especially in species described from dry specimens (Hooker 1894; Carr 1929). This tissue is to some extent similar to verrucose tissue present in G. callosa J.J.Sm., G. sabahensis and G. tembatensis P.T.Ong & P.O’Byrne (Smith 1931; Wood 2008; Ong 2015; Hroneš et al. 2024) but differs from it by smooth surface.

We would like to thank field assistants from the Institute for Biodiversity and Environmental Research (IBER) and Brunei National Herbarium (BRUN), in particular Mohamad Farid bin Abdullah and Watu bin Awok for their help in the field, and to Vojtěch Blažek, who kindly prepared an illustration of the species. We also thank the UBD Botanical Research Centre, in particular Nur Ammy Marliana Liming, for assistance with herbarium specimens. André Schuiteman and Ong Poh Teck kindly provided literature.