Monday, March 20, 2023

[Botany • 2023] Spiranthes hachijoensis (Orchidaceae: Orchidoideae) • A New Species within the S. sinensis Species Complex in Japan, based on Morphological, Phylogenetic, and Ecological Evidence

Spiranthes hachijoensis Suetsugu, 

in Suetsugu, Hirota, Hayakawa, Fujimori, Ishibashi, Hsu & Suyama, 2023. 

The systematics of the Old World Spiranthes sinensis (Pers.) Ames species complex (Orchidaceae) has been complicated by its wide distribution and morphological variations. Within the species complex, S. australis Lindl. has been generally accepted as the only Spiranthes Rich. species distributed on the Japanese mainland. The present study provides morphological, phylogenetic, and ecological evidence for the recognition of S. hachijoensis Suetsugu as a new species of the S. sinensis species complex on the Japanese mainland. Spiranthes hachijoensis is morphologically similar to S. hongkongensis S.Y. Hu & Barretto and S. nivea T.P. Lin & W.M. Lin, sharing a degenerated rostellum, pollinia without a viscidium, and distinctly trilobed stigma. However, the taxon can be morphologically distinguished from S. hongkongensis by its glabrous rachis, ovaries, and sepals, and from S. nivea by its papillate labellum disc, larger papillate basal labellum callosities, and glabrous rachis, ovaries, and sepals. The autogamy and flowering phenology (i.e., earlier flowering) of S. hachijoensis are most likely responsible for premating isolation from the sympatric S. australis. A MIG-seq-based high-throughput molecular analysis indicated that the genetic difference between S. hachijoensis and its putative sister species S. sinensis is comparable to, or even greater than, the genetic difference between pairs of other species within the S. sinensis species complex. Our multifaceted approach strongly supports the recognition of S. hachijoensis as a morphologically, phenologically, phylogenetically, and ecologically distinct species.
Keywords: Integrative taxonomy, Orchidaceae, Reproductive isolation, SNP data, Speciation, Species delimitation, Spiranthes sinensis species complex

Spiranthes hachijoensis in its natural habitat in Japan.
a–d Flowering individual observed on Hachijo Island.
e, f Flowering individual observed in Ichihara-shi, Chiba Pref. g Flowering individual observed in Kimitsu-shi, Chiba Pref. h Flowering individual observed in Nagoya-shi, Aichi Pref. i Flowering individual observed in Kagoshima-shi, Kagoshima Pref.
 Scale bars: 30 mm

Spiranthes hachijoensis Suetsugu, sp. nov.
Diagnosis: Spiranthes hachijoensis is most morphologically similar to S. hongkongensis but can be distinguished by its glabrous rachis, ovaries, and sepals.

Japanese name: Hachijo-neji-bana. ネジバナ

Kenji Suetsugu, Shun K. Hirota, Hiroshi Hayakawa, Shohei Fujimori, Masayuki Ishibashi, Tian-Chuan Hsu and Yoshihisa Suyama. 2023. Spiranthes hachijoensis (Orchidaceae), A New Species within the S. sinensis Species Complex in Japan, based on Morphological, Phylogenetic, and Ecological Evidence. Journal of Plant Research. DOI: 10.1007/s10265-023-01448-6