Saturday 2 October 2021

Thismia sitimeriamiae: A new species of Parasitic Plant from Terengganu State, Peninsular Malaysia.

The Family Thismiaceae comprises 3-5 genera (two genera are sometimes separated out and placed within a family of their own) of Parasitic Monocotyledonous Plants within the Order Dioscoreales, which also includes Yams. These Plants parasitise the Mycorrhizal Fungi of other Plants, obtaining nutrients from the Fungi, but not providing the Fungi with anything in return. The genus Thismia currently contains 86 species, predominantly from tropical Asia and Australasia, although there are species known from the Americas and temperate Asia. However, the diversity of the group is not that well understood, as these Plants, which are non-photosynthetic, only protrude above the ground during their breeding season, when they produce flowers a few centimetres high. This means that many Thismia species are known only from a single specimen, and we have little idea how widespread they really are or how much variation there is within species. 

The Malaysian state of Terengganu appears to be somewhat of a biodiversity hotspot for Thismias, whith six species reported there to date; Thismia alba, Thismia aseroe, Thismia domei, Thismia javanica, Thismia latiffiana, and Thismia terengganuensis. This diversity appears to be linked to the primary rainforests of the state, which have been disappearing rapidly in recent decades, which raises interesting conservation questions for the genus, which is hard to raise in captivity or transplant to new locations, due to its dependence on (unknown) Fungal hosts.

In a paper published in the journal Phytokeys on 29 June 2021, Mat Yunoh Siti-Munirah of the Forest Research Institute Malaysia, Nikong Dome of DigitalDome Photography, and Chris Thorogood of the Department of Plant Sciences at the University of Oxford and the University of Oxford Botanic Garden, describe a new species of Thismia from the Hulu Nerus Forest Reserve in the State of Terengganu.

Hulu Nerus Forest Reserve (black circle), where the new species was discovered. Siti-Munirah Mat Yunoh et al. (2021).

The new species was discovered by Nikong Dome beside a mountain trail in the forest reserve in 2019, and is named Thismia sitimeriamiae, in honour of his mother, Siti Meriam, honour of her unparalleled support for his conservation activities and her help in maintaining his plant collections. The species was originally discovered at two locations beside the trail in December 2019, but a return visit in February 2020 found that one of these sites had been destroyed by Wild Boar activity, and only a single Plant was growing at the other. A follow up visit in December 2020 again found only a single Plant growing at this site, and was unable to locate any other sites where the species was growing.

Thismia sitimeriamiae. (A) The habitat in Gunung Sarut, in the State of Terengganu, Peninsula Malaysia. (B) The habit of flowering specimen. (C) A fruiting specimen (in situ). Siti-Munirah Mat Yunoh et al. (2021).

Thismia sitimeriamiae produces a single conical orange flower on an unbranching stem covered by residual, scale-like, non-photosynthetic white leaves arranged in a spiral pattern. The whole Plant stands about 2.2 cm heigh, and is easily overlooked in the forest leaf-litter. 

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. Siti-Munirah Mat Yunoh et al. (2021).

The new species is currently known only from a single location, in a lowland Dipterocarp forest, growing on moist soil in shade, at an elevation of 209 m above sealevel. Since it is known only from a single location, beside a popular tourist trail where there is a high chance of Human disturbance, and less than five specimens have ever been observed, Siti-Munirah Mat Yunoh et al. recommend that the species be treated as Critically Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species

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. Images not to scale. Siti-Munirah Mat Yunoh et al. (2021).

Thismias, like other non-photosynthetic Parasitic Plants, typically spend much of their time below ground, only emerging to flower, the timing of which can be unpredictable from a Human perspective. Nevertheless, Thismia sitimeriamiae, has only been observed at two localities, flowering and fruiting between December and February, and both of those sites have subsequently been disturbed by the actions of Wild Boars, the first between the initial discovery of the Plant in December 2019 and a follow-up visit to the site in 2020, the second was discovered also to have been destroyed during a visit to the site in June 2021. 

Plants which parasitise Fungi present an interesting challenge to conservationists, since their survival is linked to specific, and usually unknown, Fungal hosts, making them hard to cultivate. Nevertheless, botanic gardens have had some success with other Parasitic Plants, including the Australian Orchid, Rhizanthella gardneri, and Rafflesia in the Philippines, although both of these had known hosts, allowing the transplanting of Plants to new areas. Most members of the genus Thismia have been recorded only once, and the ecology of these Plants is poorly understood, which makes cultivating them unlikely in the near future. This being the case, conservation efforts should be directed at the preservation of their environment as much as possible.

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