Thismia limkokthayi Siti-Munirah & E.Chan, 2022

Siti-Munirah, Mat Yunoh, Suhaida, Mustafa & Eddie, Chan, 2022, Thismia limkokthayi (Thismiaceae): A new mycoheterotrophic species from Genting Highlands in Pahang, Malaysia, PhytoKeys 211, pp. 1-11 : 1

Thismia limkokthayi Siti-Munirah & E.Chan sp. nov.

Figs 1 , 2 , 3

Diagnosis.

Thismia limkokthayi is distinguished from closely-related species by the following combination of characteristics: black to dark brown floral tube and appendages, 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.

Type.

Malaysia. Peninsular Malaysia: Pahang, Bentong District, Genting Highlands , ca. 1137 m elev., 28 April 2022, Siti-Munirah MY, FRI91138 c (holotype KEP!, spirit collection, barcode no. SC12022) .

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).

Peninsular Malaysia: Pahang, Bentong, Genting Highlands, ca. 1137 m elev., 7 April 2022, Siti-Munirah MY, Eddie C & Suhaida M, FRI91138 a (KEP, spirit collection, barcode no. SC12021) ; 7 April 2022, Siti-Munirah MY, Eddie C & Suhaida M, FRI91138 b (KEP, spirit collection, barcode no. SC12020)

Distribution.

Endemic to Peninsular Malaysia, Pahang. Currently known only from the type locality.

Ecology and habitat.

In lower montane forest and upper dipterocarp forest, on moist soil in shade, near an open space (hiking trail; 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 eco-tourism 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 second including Thismia species without appendages (e.g. T. latiffiana Siti-Munirah & Dome and T. sitimeriamiae Siti-Munirah, Dome & Thorogood).

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 Thismia 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 Thismia 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 ( Dančák et al. 2020). 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 .

Figures

Figure 1. Thismia limkokthayi with scale (all in centimetres (cm )) A plants with mature (FRI 91138 c) and young flowers with long stems B mature flower with a very short stem (FRI 91138 b) C stamens (FRI FRI 91138 a). Photos by Siti-Munirah MY.

Figure 2. Thismia limkokthayi A coralliform roots B full flower C claviform tip of mitre appendage D longitudinal section of floral tube, showing inner surface E outer tepal and inner tepal F side view of mitre G mitre viewed from above H six stamens, viewed from below I outer view of a stamen J inner view of two pendulous stamens K detail of the side lobe on the supraconnective apex (side lobe with truncate tips that are recurved inwards) L ovary with style, stigma and flower bud surrounded by bracts M stigmas. All from FRI FRI 91138 a (A, D, I, J, K, L, M), FRI 91138 b (H) and FRI 91138 c (B, C, E, F, G). Photos by Siti-Munirah MY; images not to scale (see dimensions in description and Fig. 1).

Figure 3. Thismia limkokthayi Siti-Munirah & Eddie Chan A group photo with the T. limkokthayi (white arrow) in its habitat (from left; Angan A, Siti-Munirah MY, Eddie C, Ahmad Norsidar AH and Suhaida M) B-C different stages of anthesis of T. limkokthayi in its habitat (in situ) B two mature flowers from one individual C a fresh flower (on the left) and a new young flower starting to bloom (on the right). Photos by Siti-Munirah MY.