Research Article |
Corresponding author: Mat Yunoh Siti-Munirah ( sitimunirahfrim1@gmail.com ) Academic editor: Michal Hroneš
© 2021 Mat Yunoh Siti-Munirah, Nikong Dome, Chris J. Thorogood.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Siti-Munirah MY, Dome N, Thorogood CJ (2021) Thismia sitimeriamiae (Thismiaceae), an extraordinary new species from Terengganu, Peninsular Malaysia. PhytoKeys 179: 75-89. https://doi.org/10.3897/phytokeys.179.68300
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We describe an extraordinary new species in the genus Thismia from the Terengganu State of Malaysia in the Malay Peninsula. The new species, which we name Thismia sitimeriamiae, is distinct from all other Thismia species known to science, most notably in its unique mitre configuration formed by the inner tepals and its floral surface morphology characterised by conspicuous orange trichomes. We discuss our findings in the context of underestimated species diversity in the genus Thismia and implications for their conservation. We recommend assigning T. sitimeriamiae the conservation status as Critically Endangered (CR) according to IUCN criteria.
conservation, forestry, mycoheterotrophy, species diversity, taxonomy
The Thismiaceae is a highly unusual family of flowering plants belonging to the order Dioscoreales (
Many species of Thismia have been seen or collected only once, from a single locality and their biology and ecology are poorly known. These elusive plants are visible only transiently, emerging to flower and set seed after heavy rain (
An area of exceptional diversity of the genus Thismia is the Malaysian State of Terengganu, which contains a significant reservoir of primary rainforest, although this has diminished at a rapid and alarming rate in recent decades. To date, six species of Thismia have been reported in the State of Terengganu: T. alba Holttum & Jonker, T. aseroe Becc., T. domei Siti-Munirah, T. javanica J.J.Sm., T. latiffiana Siti-Munirah & Dome, T. terengganuensis Siti-Munirah (
The distinctive structure, colour and morphology of this exceptionally rare and ephemeral plant make this species amongst the most eye-catching in the genus described from Peninsular Malaysia to date.
Our assessment is based on material collected by the second author in December 2019 and 2020 from Hulu Nerus FR, Setiu District, Terengganu (Map
Thismia sitimeriamiae has a unique combination of morphological traits, by which it differs from all its congeners including its orange colour, its surface characteristics and its floral architecture: the flower is strigose with pale orange simple and stellate trichomes covering the outer surface of the floral tube, mitre and ovary; the upper surface of the annulus is covered by very short trichomes; the outer tepals are reduced and inconspicuous and the inner tepals are curved upwards, connate, forming an umbrella/parasol-like mitre with a flattish apex.
Malaysia. Peninsular Malaysia: Terengganu, Setiu District, Hulu Nerus Forest Reserve, ca. 209 m alt., 23 December 2019, Dome Nikong, FRI 91118 (holotype KEP!, spirit collection, No. barcode 280006).
Achlorophyllous herb, ca. 2.2 cm tall. Roots coralliform, creeping, light brown. Stem 8 mm tall, erect-ascending, unbranched, 2 mm thick, whitish. Leaves ca. 6, spirally arranged, triangular, scale-like, acute, entire, 3–4 mm long and 1 mm wide at base, pale whitish. Bracts 3, widely triangular to ovate, entire, acute to acuminate, ca. 5 mm long, 2 mm wide, pale greenish to brown. Pedicel 1 mm long, elongating after anthesis, greenish. Inflorescence (flower) solitary, actinomorphic, ca. 1.5 cm long; pale to dark orange; floral tube (hypanthium) conical in shape, ca. 1 cm in height, widest (1.2 cm) in the upper part; outer surface bright orange, sparsely covered with pale orange, simple trichomes (occasionally apically stellate); inner surface partially convex/reticulum; outer tepals 3, rather reduced and inconspicuous, divided, forming a narrow overhanging fringe around the mouth of the perianth tube; inner tepals well-developed, each pale orange, distally connate, forming a flattish, umbrella-like mitre ca. 3–4 mm tall, proximally flattened with revolute margins, arching over the floral tube; mitre circular in outline, ca. 8–10 mm wide, the upper surface bright orange, covered sparsely with orange trichomes, the lower surface glabrous, bright orange; annulus (apical part of the floral tube) pale orange, rounded, ca. 1.2 cm wide, the rim raised, connected with the inner tepals; upper surface covered with short trichomes; aperture, ca. 4–5 mm, with a blackish margin; stamens 6, orange, pendent from the annulus; filaments orange, curved downwards, connectives laterally connate, forming a tube, ca. 3 mm long, glabrous on the inner surface, the apex of each connective with two lobes, each pointed with transparent trichomes; outer side of connectives forming a lateral appendage, protruding towards the floral tube, horn-like on each side, shallowly dentate and sparsely hairy on the free margins; thecae pale, surrounded by tufts of hairs; interstaminal glands inserted along the line of fusion between the connectives; ovary inferior, obconical, flushed pale orange and greenish, covered by bracts; placentas 3, parietal; pistil slender, clavate, pale greenish-orange; style ca. 1.5 mm long, slender, erect, glabrous; stigma ca. 1 mm, papillose, 3-lobed, narrowly-rectangle, each without furrowed, orange; fruit a cup-shaped capsule, greenish, borne on an elongated pedicel up to 6 cm long; seeds brown.
Illustration of Thismia sitimeriamiae A cross section of perianth showing pendulous stamens (above) and slender pistil (beneath) B pistil C aerial view of flower showing mitre and portions of apical part of floral tube and outer tepals D fruit E stamen (showing outer side of connective) F flower, lateral view G habit, showing inflorescence (flower) and roots. All illustrated from FRI 91118 (excluding D, in situ).
(paratype). Malaysia. Peninsular Malaysia: Terengganu, Setiu District, Hulu Nerus Forest Reserve, ca. 209 m a.s.l., 25 December 2020, Dome Nikong FRI 91123 (KEP, spirit collection, barcode 28007).
Thismia sitimeriamiae A habit with roots B flower, view from below C aerial view of floral tube (mitre removed) D flower, aerial view E mitre, lateral view F ovary and pistil, lateral view G flower, lateral view H mitre, lateral view I stellate trichomes on the outer surface of floral tube. All from FRI 91118 (A–F) and a plant photographed in situ (G–I). Images not to scale (see dimensions in description and Figure
Endemic to Terengganu, Peninsular Malaysia. Currently known only from the type locality (Map
Lowland dipterocarp forest on moist soil in shade at an elevation of 209 m a.s.l. Flowering and fruiting from December to February.
Thismia sitimeriamiae is dedicated to Siti Meriam, the mother of the second author (Dome Nikong), in honour of her unparalleled support for the conservation activities pursued by Dome Nikong and her help in maintaining his plant collections.
In accordance with the IUCN Red List Categories and Criteria (
Flower structure of Thismia sitimeriamiae A longitudinally dissected flower, showing inner side of stamens and pistil B stamens, (inner view) C lateral view of stamens showing lateral appendage (arrow) D lateral view of outer stamens in which interstaminal glands (arrow) are discernible. All photos from FRI 91123. For dimensions, see description and Figure
Thismia sitimeriamiae is markedly distinct from all other species of Thismia reported to date. This species possesses unique morphological features including an outer floral surface covered with mixed simple and stellate trichomes, a connate mitre formed by the inner tepals with a flat elevated, umbrella-like portion and a pistil far more slender than those of other species described which normally possess a short and thick style. Thismia sitimeriamiae is morphologically most similar to T. coronata Hroneš, Dančák & Sochor (
Morphological comparison of Thismia sitimeriamiae, T. coronata and T. kelabitiana (
Character | T. sitimeriamiae | T. coronata | T. kelabitiana |
---|---|---|---|
Height (cm) | 2.2 | 4.5–8 | 5–18 |
Stem | |||
Length (cm) | 0.8 | 2.4–4.2 | 1.5–16 |
Form | simple | branched | branched |
Colour | whitish | reddish-brown to orange | dark pinkish to reddish-brown (to almost grey or orange) |
Inflorescence (flower number) | Solitary | 1–6 | 1–3 |
Leaves | |||
Number | 6 | 4–11 | 3–10 |
Size | |||
Length (mm) | 3–4 | 2–5 | 4.5–5.5 |
Width (mm) | 1 | 1–2 | 1.8–2 |
Colour | pale, whitish | light brown to reddish | light brown to pinkish |
Bracts | |||
Shape | broadly triangular to ovate | lanceolate triangular | broadly triangular to ovate |
Margin | entire | entire to irregularly dentate | entire to irregularly dentate, often deeply dissected |
Size | |||
Length (mm) | 5 | 4–8 | 6–8 |
Width (mm) | 2 | 2–3 | 2.5–4 |
Colour | pale greenish to brown | reddish to brown | pinkish to brown |
Pedicel colour | greenish | reddish-brown to orange | dark pinkish to reddish brown (to almost grey or orange) |
Flowers | |||
Size | |||
Length (cm) | 1.5 | 1.8–2.3 | 2.6–2.8 |
Width (cm) | 1.2 | 0.7–1 | 1.2–1.3 |
Colour | pale to dark orange | dark yellow to orange | white to bright yellow |
Floral tube (hypanthium) | |||
Shape | conical | funnel-shaped towards the base, apically urceolate |
funnel-shaped towards the base, apically urceolate |
Colour | outer surface more or less uniformly bright orange | dark yellow to orange, with 6 brownish-orange, prominent longitudinal ribs alternating with 6 brown-orange longitudinal stripes on outer surface | white to bright yellow at the top, with six brownish non-prominent longitudinal ribs and six yellow to brown longitudinal stripes on outer surface |
Surface texture | |||
Outer | sparsely covered with pale orange, simple trichomes (occasionally apically stellate) | glabrous (trichomes absent) | glabrous (trichomes absent) |
Inner | inner surface partly convex/reticulum | inner surface weakly reticulated, especially apically | inner surface reticulated |
Outer tepals | 3, rather reduced and inconspicuous, somewhat divided along the margin to form a narrow, inconspicuous fringe around the floral tube mouth | 3, conspicuous, entire or slightly sinuate, often single-toothed, forming a fringe around the floral tube mouth | 3, deeply divided into 8-10 acute lobes forming a conspicuous fringe around the floral tube mouth |
Inner tepals (and mitre) | pale whitish-orange, distally connate, forming an elevated, more or less circular, umbrella-like mitre; lobes proximally flattened with revolute margins (not filiform), arched over the floral tube; upper surface covered sparsely with conspicuous orange trichomes | orange, distally connate, forming an elevated, more or less flat, triangular mitre; lobes proximally filiform, pillar-like, arched over the floral tube; trichomes absent | bright yellow to brownish-yellow, distally connate, forming a conspicuously elevated, more or less triangular mitre; lobes proximally filiform, pillar-like, arched over the floral tube; trichomes absent |
Annulus (apical part of floral tube) | present (upper surface covered with short trichomes) | absent | absent |
Connectives | |||
Colour | orange | white | white |
Length (mm) | 3 | 5–6 | 7 |
Inner surface | glabrous | with prominent longitudinal rib extending along inner side | with prominent longitudinal rib extending along inner side |
Apex of each connective | 2 lobes, each pointed with a transparent trichome | 1 central lobe (extension of rib) and 2 smaller lobes, each lobe with a long transparent trichome | 1 central lobe (extension of the rib) and 2 smaller lobes pointing somewhat centrifugally, each with a transparent trichome |
Outer surface | lateral appendage protruding towards floral tube, horn-like on each side, shallowly dentate and sparsely hairy on free margins | lateral appendage box-shaped, protruding towards floral tube, not reaching apex of connective, shallowly dentate and hairy on apical margin, with tufts of hairs on lateral margins | lateral appendage box-shaped, protruding towards perianth tube, not reaching the apex of the connective, shallowly dentate and sparsely hairy on free margins |
Ovary | |||
Colour | flushed pale orange and greenish | dark brown | dark reddish-brown |
Pistil | |||
Style | slender | short | short |
Stigma | lobes narrowly-rectangular, not furrowed; orange | lobes rectangular, longitudinally furrowed; dark brown | lobes rectangular, longitudinally furrowed; dark reddish-brown |
Capsule | |||
Colour | greenish | pale brown to reddish at maturity | dark brown to blackish or reddish, maturing to become pinkish |
Pedicel | elongated to 60 mm | 10–25 mm | very short (dimensions not known) |
We should note that our assessment of T. sitimeriamiae is based on a very limited sample due to the rarity of the plant and a paucity of material. Similar challenges were encountered for other species in this taxonomically difficult genus in PM, for example, T. chrysops, T. fumida, T. racemosa and T. kelantanensis (
The mating system and reproductive ecology of T. sitimeriamiae are unknown, as with most species of Thismia.
We assess T. sitimeriamiae as Critically Endangered (CR B2 ab (ii,iii)) in accordance with the IUCN Red List Categories and Criteria because it is known only from the type locality, where just four individuals have been observed in total, including two flowering specimens in December 2019, one in fruit in February 2020 and a further specimen in flower in December 2020. The type locality is on a tourist trail within a forest reserve. Due to the sensitivity and human footfall of the habitat, the risk of disturbance is high. T. sitimeriamiae is probably unpredictable in appearance, like other species in the genus. Based on the authors’ long-term observations of the type locality and associated areas, the species is exceptionally rare or absent elsewhere. Furthermore, based on recent observations by the second author (June 2021), the only known location of the plant has been destroyed by wild boar activity, meaning that the species is now at considerable risk of extinction.
Mycoheterotrophic plants, such as Thismia, present an interesting challenge in plant conservation. Most are probably intractable to cultivation due to their very exacting ecologies and dependency on specific fungal partners. Botanic gardens could play a part in the conservation of Thismia as they have for other intractable plants. For example, botanic gardens have played a role in the conservation of the mycoheterotrophic orchid Rhizanthella gardneri in Australia through survey work and successful transplant and propagation (
Since the most comprehensive taxonomic revision of the genus Thismia in the 1930s and 40s (
This research was carried out as part of the Flora of Peninsular Malaysia Project (FPM) at the Forest Research Institute Malaysia (