﻿Thismialimkokthayi (Thismiaceae): A new mycoheterotrophic species from Genting Highlands in Pahang, Malaysia

﻿Abstract Thismialimkokthayi, a distinct mitriform species of the mycoheterotrophic genus Thismia, is described and illustrated. It was found at a locality in the upland areas of Genting Highlands, Pahang, Malaysia. This new species is morphologically similar to members of Thismiasect.Geomitra, but differs in several characteristics, including the colour of the floral tube, the inner surface of the floral tube with longitudinal ribs and absent transverse bars, a stamen apex with a central lobe (prolongation of the rib) and two lateral lobes (the tips of each are recurved) and a black-purplish stigma. Thismialimkokthayi is provisionally classified as Critically Endangered according to the IUCN Red List Categories and Criteria.


Introduction
Fairy lanterns, Thismia Griff. (1844) (Thismiaceae), are non-photosynthetic mycoheterotrophic herbs distributed mainly in the tropics. The number of known species of this genus has increased rapidly in recent years. Currently, approximately 96 species are known (Imhof 2010 onwards;Siti-Munirah et al. 2021;Chantanaorrapint and Seelanan 2021;Siti-Munirah and Dome 2022). To date, three species of Thismia are known in Pahang State: T. alba Holttum & Jonker, T. aseroe Becc. and T. racemosa Ridl. (Jonker 1948;Chua and Saw 2006). Morphologically, all of these species belong to Thismia sect. Thismia subsect. Odoardoa, in which all the tepals are fully open, spreading and not forming any mitre as in sect. Geomitra.
During a routine assessment of work progress near the Clearwater Way trail, located in a private forest not far from the Resorts World Genting Awana Hotel (Genting Highlands, Bentong District, Pahang), an unknown plant was discovered. The discovery was made on 1 April 2022, by the third author, who observed the unknown plant in a population growing on the nature trail. Based on images sent to the first author for identification, it was suspected to be a new taxon of Thismia. Later (7 April 2022), we visited the site together and were able to find additional plants within the same population. Several plants were collected for the herbarium and for taxonomic study. After careful examination, the specimens were found to have some novel features in terms of flower tube and tepal morphology. These features formed a unique combination of characteristics that were not matched with any of the described species of Thismia. Therefore, we now describe a new species that we have named Thismia limkokthayi Siti-Munirah & E.Chan. This additional new species brings the number of currently known species of Thismia in Pahang to four. This discovery has also resulted in T. limkokthayi becoming the first mitriform (Geomitra) species reported in the State of Pahang.

Materials and methods
This study is based on material collected on 7 April 2022 from Genting Highlands Forest, Bentong District, Pahang (Map 1), on private land near the Resorts World Genting Awana Hotel, which is one of the flagships for tourism in the mountains of this region. Genting Highlands is a famous mountainous region in Bentong District, Pahang, located approximately 50 km from the capital of Malaysia, Kuala Lumpur. Genting Highlands is renowned for entertainment, hospitality and tourism, as well as nature. As an area with an exceptional diversity of flora and fauna, it is home to a significant reservoir of primary rainforest (more than 15,000 acres); however, part of the area is fully developed.
One of the collected individuals was observed during its flowering growth (in the office at the Forest Research Institute Malaysia (FRIM)) and was selected as holotype (FRI91138c) due to its perfect condition. Morphological characteristics were examined by stereomicroscopy and high-resolution macrophotography. Measurements were made on fresh and liquid preserved material. The specimen was thoroughly compared with original drawings and descriptions in the protologues of Thismia sect. Geomitra.  the presence of mitre fovea between the bases of claviform appendages, the presence of longitudinal ribs and absent transverse bars on the inner side of the floral tube, the apex of stamens with a central lobe (prolongation of the rib) and two lateral lobes (the tips of each are recurved) and dark purple stigma.
Achlorophyllous herbs up to ca. 14 cm. Roots coralliform, surface hairy, apices brownish-white. Stems up to ca. 4.5 cm tall or very short (possibly for young plants), ca. 2-3 mm in diameter, erect, ascending, white and becoming brownish with age, glabrous, terete. Leaves glabrous, pale brown, dark brown in the upper part or towards the apex, scale-like, triangular-ovate to lanceolate, up to 12 mm long, 3 mm wide at the base, apex acute to acuminate, spirally arranged, more crowded in the upper part of the stem. Floral bracts 3, pale brown to dark brown towards the apex, similar to upper leaves, but slightly larger, 10-12 mm long, apex acute to acuminate, 2 mm wide at the base. Pedicels lengthen up to 5 mm during flower growth, 2-3 mm wide. Flowers solitary or in clusters of 2, opening in succession in the latter case and forming loose monochasial inflorescences, lateral flower located in the axil of one of the floral bracts of the terminal flower and also bearing its own floral bracts; each flower up to 8 cm long (including ovary and appendages); perianth actinomorphic with 6 tepals fused to form a floral tube with a dome-shaped mitre with 3 slender, claviform appendages on its top; floral tube black brownish/brown blackish, urceolate, ca. 20-25 mm long, ca. 5-10 mm wide, constricted just above the ovary, widest in the upper part; outer surface with 6 longitudinal ribs, glabrous, rough, black to dark brown; inner surface with 6 greenish longitudinal ribs, without transverse bars, black to dark brown; outer tepal lobes 3, brownish orange, minute, ca. 1 mm long, 7 mm wide at base, broadly triangular, erect; inner tepal lobes 3, black to dark brown, thick, cuneate, surface glabrous, apically adnate to form a dome-shaped mitre; mitre with 3 lateral, round-shaped, ca. 8-10 mm wide apertures, 3 hood-like accessory lobes, more curved during the early stages of flowering and flattening when the flower is older and matured; mitre appendages each ca. 27-30 mm long, their base wide and flattened, forming a fovea in the centre of the mitre, becoming narrower above, claviform at apex, glabrous, dark brown to pale orange towards tip. Stamens 6, pendulous from the apical margin of the floral tube; annulus absent; filaments orange and white, curved downwards, with bases slightly emerged above floral tube apex, not connate, forming 6 apertures apparent when viewed from above; connectives broad, orange-yellowish in lower half and black/dark brown in upper half, laterally connate to form a tube, ca. 12 mm long, each with prominent longitudinal rib extending along the entire length of the inner surface of the connective; supraconnective apex with one central lobe (extension of the rib) and two smaller side lobes with tips recurved inwards/truncate, glabrous; lateral appendage skirt-like, black, protruding towards the floral tube, not reaching connective apex, glabrous including on margins, only sparsely hairy on each horn-like corner; individual stamens with 2 thecae (abaxial, dehiscing towards the inner surface of the floral tube), each theca oblong, 2 mm long; interstaminal glands elliptic-oblong, translucent, inserted on the line of fusion between connectives. Ovary inferior, obconical, ca. 4-5 mm long, brown to dark, with 6 longitudinal ribs, unilocular; placentas 3; style short, ca. 0.3 mm long, black/purplish; stigma 3-lobed, black-purplish, stigma lobe oblong, ca. 3 mm long, folded, bifid at apex, surface slightly papillose. Fruit not observed.
Additional specimens examined (paratypes).  Fig. 3A) and sloping area. This species occurs in a healthy undisturbed forest at an altitude of about 1137 m. The site is in a private forest and within a watershed. The forest area remains intact, apart from where it was affected by recent flooding and water surge (19 December 2021). The impact of this natural disaster completely reshaped part of the river area. However, this area is currently recovering. Fortunately, the only known population of Thismia limkokthayi is located away from the riverbank, on the slope of the main trail. As a result of this discovery, the trail was moved to another part of the forest. The flowering period is from March to April.
Etymology. Thismia limkokthayi was named in honour of Tan Sri Lim Kok Thay, Chairman of the Genting Group, who is closely involved in efforts to develop ecotourism facilities and amenities supporting the preservation and sustainability of important biodiversity assets and sites in Genting Highlands.
Preliminary conservation status. Following the IUCN Red List Categories and Criteria (IUCN 2019), this species has been assessed as Critically Endangered (CR B2ab (iii); D) due to its small population and threats to its microhabitat. It is currently known from only one locality (the type locality) and is certainly a very rare species since only three individuals have been observed. Although the type locality is in a private forest, it may be exposed to future tourist activities in the Resorts World Genting Awana area. The habitat of the species is located on the original trail leading from the entrance of Clearwater Way to Chin Swee Caves Temple. However, since this is private land, the protection of this area from disturbance remains possible. As such, efforts must be made to locate this species in the surrounding area.
Notes. Thismia species are characterised by their peculiar appearance and flower morphology, which are distinctive and simultaneously very diverse (Shepeleva et al. 2020). Most Thismia species have various unique structural combinations. Amongst them, there are species belonging to the Thismia group of which inner tepals are fused together in their upper part and form a roof-like or hat-like structure called a mitre. In Peninsular Malaysia, there are two groups of mitriform Thismia: first including Thismia species with mitre appendages (e.g. Thismia clavigera, Thismia kelantanensis and T. clavigeroides) and Thismia limkokthayi is easily recognised by a combination of the following characteristics: coralliform roots, erect outer perianth lobes, mitriform inner perianth lobes with three erect, slender, claviform appendages that form a mitre fovea with their flattened bases in the centre, absence of the annulus, presence of longitudinal ribs on the inner side of the floral tube (or absence of the reticulate inner side), the apex of stamens with a central lobe (prolongation of the rib) and two lateral lobes (the tips of each are recurved) and black-purple stigma.
Based on the infrageneric classification of Kumar et al. (2017), T. limkokthayi superficially resembles Thismia species in the Thismia subgenus Thismia section Geomitra (Becc.) Kumar & S.W. Gale, mainly based on the presence of inner tepals forming a mitre, each with filiform appendage and central mitral appendages that are free from each other, with the outer tepals always being short (less than 2 mm long). Two species were included in section Geomitra: T. clavigera (Becc.) F. Muell. and T. betung-kerihunensis Tsukaya & H. Okada. To date, T. limkokthayi has not been included in any DNA-based analysis. According to the classification proposed by Shepeleva et al. (2020), T. limkokthayi is possibly related to species in clade 3 because it is characterised by coralliform roots, inner tepals fused into a mitre and free mitre appendages extending from a central point. Within clade 3 (i.e. section Sarcosiphon sensu Jonker 1948), there are two morphologically distinct groups characterised by the presence of a prominent central rib along the inner side of the connective and the absence of an annulus . They can be distinguished by the presence of distinct appendages at the top of the mitre (T. clavigera group) or their absence (T. goodii group). However, their exact relationship cannot be clarified until more species in both groups are sequenced.
Currently, there are five species known in the T. clavigera group: T. betung-kerihunensis, T. clavigera, T. clavigeroides Chantanaorr & Seelanan, T. kelantanensis Siti-Munirah and T. sumatrana Suetsugu & Tsukaya (Tsukaya and Okada 2012;Siti-Munirah 2018;Suetsugu et al. 2018;Chantanaorrapint and Seelanan 2021). Thismia limkokthayi clearly differs from all these species by the absence of transverse bars on the inner surface of the floral tube. Notably, T. limkokthayi clearly resembles T. kelantanensis, an endemic species from Kelantan (Malay Peninsula), which also has three slender, claviform appendages at the tip of the mitre and erect outer tepals. However, T. kelantanensis is easily distinguished from T. limkokthayi by its bluish filaments and stamens, as well as the six-part cap on the mitre. Additionally, it also resembles T. clavigeroides Chantanaorr & Seelanan from Thailand and T. sumatrana Suetsugu & Tsukaya from Sumatra in its general appearance. However, T. limkokthayi differs from both of these species by the curved outer lobes on the supraconnective apex. Moreover, the connective appendage of T. sumatrana is hairy, while it is glabrous in T. limkokthayi and the flower colour of T. clavigeroides (including the stamens) is almost whitish, while that of T. limkokthayi is blackish-brown. A comparison of morphological characteristics between T. limkokthayi and other related species is presented in Table 1. Table 1. Morphological differences between Thismia limkokthayi and related species. The characters of previously-described species are taken from the protologues and recent publications on T. betungkerihunensis (Tsukaya and Okada 2012), T. clavigera (Chantanaorrapint and Chantanaorrapint 2009), T. kelantanensis (Siti-Munirah 2018) and T. sumatrana (Suetsugu et al. 2018).