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| Monotropastrum kirishimense Suetsugu, in Suetsugu, Hirota, Hsu, ... et Suyama, 2022. |
Abstract
Due to their reduced morphology, non-photosynthetic plants have been one of the most challenging groups to delimit to species level. The mycoheterotrophic genus Monotropastrum, with the monotypic species M. humile, has been a particularly taxonomically challenging group, owing to its highly reduced vegetative and root morphology. Using integrative species delimitation, we have focused on Japanese Monotropastrum, with a special focus on an unknown taxon with rosy pink petals and sepals. We investigated its flowering phenology, morphology, molecular identity, and associated fungi. Detailed morphological investigation has indicated that it can be distinguished from M. humile by its rosy pink tepals and sepals that are generally more numerous, elliptic, and constantly appressed to the petals throughout its flowering period, and by its obscure root balls that are unified with the surrounding soil, with root tips that hardly protrude. Based on genome-wide single-nucleotide polymorphisms, molecular data has provided clear genetic differentiation between this unknown taxon and M. humile. Monotropastrum humile and this taxon are associated with different Russula lineages, even when they are sympatric. Based on this multifaceted evidence, we describe this unknown taxon as the new species Monotropastrum kirishimense. Assortative mating resulting from phenological differences has likely contributed to the persistent sympatry between these two species, with distinct mycorrhizal specificity.
Keywords: Fungal association, Integrative taxonomy, Mycoheterotrophy, Mycorrhizas, Reproductive isolation, SNP data, Speciation, Species delimitation
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| Monotropastrum kirishimense and its monotropoid association (holotype). a Flowering scape with root ball. b, c Flowering plants. d Flowers, top view. e, f Magnification of the root ball. Root tips are not apparent, but white fungal hyphae are visible. Arrowheads indicate the root tip apices. Scale bars: 3 cm (a–c), 1 cm (d, e), and 5 mm (f). Photographed by Kenji Suetsugu |
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| Monotropastrum humile and its monotropoid association found at the M. kirishimense type locality (on June 25, 2019, except for the flowering plants). a Flowering plants (on May 17, 2019). Arrowheads indicate spreading sepals. b Fruiting plant. c Fruiting scapes with root ball. d, e Magnification of the root ball. Root tips and branching are easily recognizable. Arrowheads indicate root tip apices. Scale bars: 3 cm (a–c), 1 cm (d), and 5 mm (e). Photographed by Hideo Shimada (a) and Kenji Suetsugu (b–e) |
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| Morphological comparison of the aboveground parts of Monotropastrum kirishimense and M. humile. Monotropastrum kirishimense in a Fujieda-shi, Shizuoka Pref., b Ena-shi, Gifu Pref., and c Kirishima-shi, Kagoshima Pref. Monotropastrum humile in d Waga-gun, Iwate Pref. and e Tarumizu-shi, Kagoshima Pref., and f M. humile f. roseum in Sakyo-ku, Kyoto Pref. Arrowheads indicate spreading sepals. Scale bars: 3 cm. Photographed by Masayuki Sato (a), Katsumi Iwahori (b), Shuichi Kurogi (c), Shin Terui (d), Kazushige Uemori (e), and Kenji Suetsugu (f) |
Monotropastrum kirishimense Suetsugu, sp. nov.
Diagnosis. Monotropastrum kirishimense is similar to M. humile but differs in its rosy pink tepals, more numerous (4–11) elliptic sepals constantly appressed to the petals throughout its flowering period, and obscure root balls unified with the surrounding soil, with little protrusion of the root tips.
Etymology. The species is named after the type locality, Kirishima. To distinguish it from Monotropastrum humile f. roseum (beni-bana-gin-ryo-so, in Japanese) described by Honda (1957), we use Kirishima-gin-ryo-so as a Japanese name, after the type locality.
Japanese name. Kirishima-gin-ryo-so
「キリシマギンリョウソウ」
Kenji Suetsugu, Shun K. Hirota, Tian-Chuan Hsu, Shuichi Kurogi, Akio Imamura and Yoshihisa Suyama. 2022. Monotropastrum kirishimense (Ericaceae), A New Mycoheterotrophic Plant from Japan based on Multifaceted Evidence. Journal of Plant Research. DOI: 10.1007/s10265-022-01422-8
