Spiranthes minamitaniana Suetsugu, 2023

Suetsugu, Kenji & Suyama, Yoshihisa, 2023, Spiranthes minamitaniana (Orchidaceae), a new orchid species from Japan based on morphological and phylogenetic data, Phytotaxa 599 (3), pp. 139-149 : 145-147

Spiranthes minamitaniana Suetsugu , sp. nov. ( Figs. 1–3 )

Type. JAPAN. Miyazaki Pref.: Koyu County, Kawaminami Town, Kawaminami Marsh , 13 May 2018, Tadashi Minamitani Ss 146-1 (holotype: KYO!, herbarium sheet and spirit collection labeled as the same specimen) .

Diagnosis. Spiranthes minamitaniana is morphologically most similar to S. hachijoensis but differs from S. hachijoensis by semicircular, weakly- or non-3-lobed stigma, and more conspicuous anther cap.

Description. Plants 15–35 cm tall. Roots fleshy, fasciculate, slender to tuberous, up to ca. 5 mm in diameter. Leaves 2–6, basal, forming a rosette, erect and spreading, narrowly lanceolate, 21–76 × 3–7 mm, apex acute to acuminate, with an indistinct petiole-like base. Inflorescence terminal, racemose erect, 15–35 cm, glabrous, with 1–3 sterile bracts sheathing the peduncle; rachis 4.1–14.3 cm, with 24–49 spirally arranged flowers; floral bracts shorter or longer than pedicellate ovary, ovate-lanceolate, 5.4–8.6 mm long, 2.0– 3.6 mm wide, glabrous, apex acuminate. Ovary sessile or with inconspicuous pedicel, pale green, ellipsoid-obovoid, 3.5–6.9 mm long, 1.5–2.7 mm wide, glabrous. Flowers resupinate, horizontal or nodding, barely to weakly opening. Dorsal sepal entirely white or pinkish purple with a basal white part, narrowly triangular, 3.3–4.2 mm long, 1.2–1.5 mm wide, glabrous, apex obtuse or rarely acute, connivent with petals and forming a hood over column. Lateral sepals entirely white or pinkish purple with a basal white part, narrowly triangular to lanceolate, slightly oblique at approximately halfway of the length, 3.3–4.2 mm long, 0.8–1.0 mm wide, glabrous, apex obtuse or acute. Petals entirely white or pinkish purple with a basal white part, linear to oblanceolate, occasionally slightly oblique at approximately halfway of the length, 2.7–3.3 mm long, 0.8–1.0 mm wide, glabrous, apex rounded. Labellum white, weakly recurved downward at about two-thirds the distance from the claw to labellum apex, oblong to slightly constricted near the reflection and then dilating below, centrally papillate near the apex, 3.2–4.1 mm long, 1.4–1.6 mm wide below the callosities, 1.4–1.6 mm wide at widest point below recurvature; margin entire to slightly undulating from the base until the area of recurvature, below point of recurvature margin becoming ruffled and lacerate; two basal callosities transparent, obovate to subglobose, papillate, 0.5–0.7 mm long, 0.5–0.6 mm wide. Column translucently white to pale green dorsally, pale green ventrally, clavate, 1.6–1.9 mm long; anther cap yellow-brown, ovate, partly embedded on the upper part of column, 1.0– 1.6 mm long; pollinia 2, each 2-partite, yellow, granular-farinaceous, without viscidium at the narrower end, 1.0– 1.1 mm long; rostellum narrow, typically lacking; stigma semicircular, weakly- or non-3-lobed, filled with viscid liquid, 0.4–0.9 mm long. Fruit ellipsoid-obovoid, 4.9–9.4 mm long, 2.2–4.0 mm wide, glabrous. Seed fusiform, ca. 0.6 mm long; embryo 1, ellipsoid, ca. 0.15 mm long.

Japanese name. Osuzu-neji-bana

Distribution. Japan (Kawaminami Marsh and Takanabe Marsh, Miyazaki Pref.). Despite the long-term searches by the authors during the flowering season around the populations, the species has yet to be discovered elsewhere. The scarcity of additional sightings during surveys specifically targeting S. minamitaniana suggests that the species is quite rare and has a highly fragmented distribution. However, S. minamitaniana may have been mistaken for more widespread species, such as S. hachijoensis , which share a similar morphology. Further surveys and detailed morphological examination of Spiranthes in wetlands may reveal a broader distribution, given that S. minamitaniana has only been observed in wetlands or marshes.

Conservation status. Spiranthes minamitaniana is currently recognized in only two populations located ca. 10 km apart, where approximately 30 individuals have been observed in total. Therefore, it can be considered critically endangered, according to IUCN criteria ( IUCN 2019) under D1 criteria, in which the number of mature individuals is less than 50.

Additional specimens examined (paratype). JAPAN. Miyazaki Pref.: Koyu County, Kawaminami Town , Kawaminami Marsh, 13 May 2018, Tadashi Minamitani Ss 146-2 ( KYO) ; loc. cit., 6 May 2021, Tadashi Minamitani Ss 204-1 ( KYO) ; loc. cit., 6 May 2021, Tadashi Minamitani Ss 204-2 ( KYO) ; loc. cit., 6 May 2021, Tadashi Minamitani Ss 204-3 ( KYO) ; loc. cit., 6 May 2021, Tadashi Minamitani Ss 204-4 ( TNS) ; loc. cit., 6 May 2021, Tadashi Minamitani Ss 204-5 ( TNS) ; Koyu County, Takanabe Town, Takanabe Marsh , 14 May 2018, Tadashi Minamitani Ss 147-1 ( KYO, herbarium sheet and spirit collection labeled as the same specimen) ; loc. cit., 14 May 2018, Tadashi Minamitani Ss 147- 2 ( KYO) .

Figures

FIGURE 1. Spiranthes minamitaniana in its type locality. (A) Habit. (B) Inflorescence with whitish cleistogamous flower. (C–D) Flower. Scale bars: 30 mm (A) and 5 mm (B–D).

FIGURE 2. Spiranthes minamitaniana with reddish pink normal flower (Tadashi Minamitani Ss146, KYO). (A) Inflorescence. (B) Flower, lateral view. (C) Flower, dorsal view. (D) Dorsal sepal. (E) Petal. (F) Lateral sepal. (G) Labellum. (H) Close-up of basal callosities of labellum. (I) Ovary and column. (J) Column, ventral view. (K) Column, dorsal view. (L) Pollinarium. Scale bars: 20 mm (A), 3 mm (B–G), 0.5 mm (H) and 1 mm (I–M).

FIGURE 3. Spiranthes minamitaniana with whitish cleistogamous flower (Tadashi Minamitani Ss147, KYO). (A) Inflorescence. (B) Flower and bract. (C) Flower. (D) Ovary and column. (E) Column, ventral view. (F) Column, dorsal view. Scale bars: 1 mm. Photographed by Masayuki Ishibashi.