Spiranthes hachijoensis occurs in Kyushu, Shikoku, Chubu, and Kanto districts of Japan.
Spiranthes hachijoensis in Ena-shi, Japan: (a) inflorescence; (b) flower, lateral view; (c) flower, top view; (d) dorsal sepal; (e) petal; (f) lateral sepal; (g) labellum; (h) close-up of basal labellum callosities; (i) ovary and column; (j, k) column, bottom view; (l) column, top view; (m) pollinia without a viscidium. Scale bars – 20 mm in (a), 3 mm in (b-g), 0.5 mm in (h), and 1 mm in (i-m). Image credit: Suetsugu et al., doi: 10.1007/s10265-023-01448-6.
Spiranthes is a genus of orchids in the subfamily Orchidoideae, commonly known as ladies tresses.
It includes approximately 50 species widely distributed across the tropical and temperate regions of the Americas, Eurasia, and Australia.
Nonetheless, the delimitation of closely related Spiranthes species based on morphology alone is hindered by phenotypic plasticity, convergent morphological features, and hybridization.
In particular, the systematics of the Old World Spiranthes sinensis species complex has been complicated by the wide distribution and morphological variation of the group.
“The genus Spiranthes encompasses a captivating and gorgeous variety of orchids, which exhibit an array of distinctive morphological traits,” said Kobe University’s Professor Kenji Suetsugu and colleagues.
“The flowers are typically small and white or pinkish, and arranged in a spiral around a central stalk, hence the moniker ladies’ tresses.”
“For a long time, it was believed that Spiranthes on the Japanese mainland constituted a single species: Spiranthes australis.”
“However, while conducting extensive field surveys focused on Japanese Spiranthes specimens, we came across several populations of an unknown Spiranthes species with hairless flower stems, on the mainland of Japan.”
Named Spiranthes hachijoensis, the new species grows alongside Spiranthes australis but blooms about a month earlier, thus leading to reproductive isolation between the two species.
It is between 8 and 25 cm tall, and has fleshy, slender to tuberous, roots up to 5 mm in diameter.
“We embarked on a comprehensive and multifaceted ten-year study to determine precisely how these plants differed,” the researchers explained.
“Specimens were collected from various locations in Japan, Taiwan, and Laos.”
“By integrating results from DNA analysis, morphology, field observations, and reproductive biology, we discovered that it is a cryptic species that exhibits a high level of molecular divergence, albeit with minimal morphological differentiation.”
“While we found that the new species is distributed in Kyushu, Shikoku, Chubu, and Kanto districts, Spiranthes hachijoensis is much rarer than its sympatric closely related species Spiranthes australis,” the authors said.
“Each population often harbors less than 20 individuals, and even in the type locality that sustains the largest number of individuals, the population size is approximately 100.”
“Therefore, we classify its conservation status as Vulnerable based on IUCN criteria under criterion D1, which states that the number of mature individuals is less than 1,000.”
The discovery of Spiranthes hachijoensis is described in a paper published in the Journal of Plant Research.
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K. Suetsugu et al. Spiranthes hachijoensis (Orchidaceae), a new species within the S. sinensis species complex in Japan, based on morphological, phylogenetic, and ecological evidence. J Plant Res, published online March 17, 2023; doi: 10.1007/s10265-023-01448-6
