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| Relictithismia Suetsugu & Tagane, Relictithismia kimotsukiensis Suetsugu, Yas.Nakam. & Tagane, in Suetsugu, Nakamura, Nakano et Tagane, 2024. |
Abstract
The family Thismiaceae, known as “fairy lanterns” for their urn- or bell-shaped flowers with basally fused tepals, consists of non-photosynthetic flowering monocots mainly in tropical regions, extending into subtropical and temperate areas. Here, we propose a new mycoheterotrophic genus, Relictithismia Suetsugu & Tagane (Thismiaceae), with its monotypic species Relictithismia kimotsukiensis Suetsugu, Yas.Nakam. & Tagane from Kimotsuki Mountains in the Osumi Peninsula, Kagoshima Prefecture, Kyushu Island, southern Japan. Relictithismia resembles Haplothismia Airy Shaw in having a cluster of tuberous roots, a feature previously observed only in this genus within the family Thismiaceae. However, it differs in having solitary flowers (vs. 2–6-flowered pseudo-raceme in Haplothismia), anther thecae largely separated (vs. connate), and the presence of an annulus (vs. absent). Additionally, Relictithismia differs from the geographically overlapping genus Thismia Griff. in its stamen structure and the position of the annulus. In Relictithismia, the stamens lack connectives, and its free filaments arise from the annulus located inside the perianth mouth, while in Thismia, the stamens typically have connate connectives, forming a staminal tube pendulous from the annulus located at the mouth of the floral tube. Our morphological and phylogenetic data indicated that R. kimotsukiensis holds an early-diverging position within the family, situated outside the Old World Thismia clade. This paper offers an extensive description and color photographs of R. kimotsukiensis, complemented by notes on its phylogenetic relationship and evolutionary history.
Keywords: Angiosperms, Endemic, Flora, Dioscoreales, East Asia, Taxonomy
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| Relictithismia kimotsukiensis. a Habit. b Close-up of root surface. c Longitudinal section of flower. d Anther. e Stigma surface. f Immature fruit. Materials from Y. Nakamura & S. Tagane 23060901 (KAG). Drawn by S. Tagane |
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| Relictithismia kimotsukiensis. a Habit. b Flower, top view. c Flower, diagonal top view. d Flower, lateral view. e Tuberous roots. f Close-up of root. g Longitudinal section of floral tube showing stamens, style, and stigma. h Longitudinal section of floral tube with stamens. i Style and stigma. j Annulus and stamens. k Anthers. l Transverse section of ovary with three equal placentas and numerous ovules. Materials from Y. Nakamura & S. Tagane 23060901 (a–f, h–l for TNS, g for KAG). Scale bars: 10 mm (a), 5 mm (b–e and g–h), and 1 mm (f and i–l) |
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| Relictithismia kimotsukiensis and its habitat at the type locality. a & b A secondary evergreen broad-leaved forest where R. kimotsukiensis was found. c & e Flower, top view. d & f Flower, lateral view. Scale bars: 10 mm. Photos (a & b) were taken by Yasunori Nakamura on 3 June 2022, and photos (c–f) were taken by Shuichiro Tagane on 9 June 2023. Photos (e & f) were captured after collection |
Relictithismia Suetsugu & Tagane, gen. nov.
Diagnosis Relictithismia resembles Haplothismia in possessing a cluster of tuberous roots, yet it is clearly distinguished by its solitary flowers (vs. 2–6-flowered pseudo-raceme in Haplothismia), largely separate anther thecae (vs. connate), and the presence of an annulus (vs. absence).
Etymology: The name of the new genus, Relictithismia, is a combination of the Latin word “relictus”, meaning “left behind”, and the generic name Thismia. The name reflects its morphological characteristics that serve as a bridge between the early-diverging genera in Thismiaceae and the genus Thismia, showcasing the putative ancestral condition of these plant groups.
Relictithismia kimotsukiensis Suetsugu, Yas.Nakam. & Tagane, sp. nov.
Etymology: The species epithet refers to the type locality of the new species.
Vernacular name: Mujina-no-shokudai (in Japanese). The vernacular name is inspired by its apparent resemblance to and the distinct diffrences from species of Thismia, locally referred to as “tanuki-no-shokudai,” meaning a candlestick used by a raccoon dog. The term “mujina” is an old Japanese name for a badger, known as “anaguma” in Japanese, although historically and regionally, it has sometimes also been associated with raccoon dogs. Therefore, we consider that this name aptly represents the similarity and differences between Thismia and Relictithismia. Moreover, the name “mujina-no-shokudai” (= a candlestick used by a badger) fits its ecology, as the majority of the plant, even during the flowering stage, remains buried underground beneath fallen leaves, reminiscent of a badger burrowing underground.
Distribution Japan, Kagoshima Pref., Kimotsuki-gun, Kimotsuki-cho (currently known only from the type locality).
Kenji Suetsugu, Yasunori Nakamura, Takafumi Nakano and Shuichiro Tagane. 2024. Relictithismia kimotsukiensis, A New Genus and Species of Thismiaceae from southern Japan with discussions on its phylogenetic relationship. Journal of Plant Research. DOI: 10.1007/s10265-024-01532-5