Diurideae

Averyanov, Leonid V., Nguyen, Van Canh, Truong, Ba Vuong, Nguyen, Khang Sinh, Nguyen, Cuong Huu, Maisak, Tatiana V., Doan, Nga Thi, Nguyen, Tuan Hoang, Pham, Van The, Dat, Pham Thi Thanh, Thai, Tran Huy, Nguyen, Van Khuong & Trinh, Ngoc Bon, 2023, New orchids in the flora of Vietnam VI (Orchidaceae, tribes Arethuseae, Cymbidieae, Diurideae, Epidendreae, Vandeae, and Vanilleae), Phytotaxa 597 (2), pp. 87-110 : 100

Tribe Diurideae

Stigmatodactylus sikokianus Maxim. ex Makino (1891: 70 t. 43), Ohwi (1965: 337), Chen et al. (2009: 88), Pedersen, Suksathan (2013: 65), Lin et al. (2016: 118), Zhou et al. (2016: 128). Type: — JAPAN. Tosa, Mt. Yohogura, Sept. 4, 1859, T. Makino (not located). ( Fig. 6 )

Ecology and phenology:—Small lithophytic and terrestrial herb. Primary evergreen broad-leaved forests, commonly on mossy rocks along streams at an elevations of 1000–1500 m a.s.l. Very rare. Flowers in July–August.

Distribution:— VIETNAM, Dak Lak Province (Lak, and Krong Bong districts). Thailand, E China, Japan.

Conservation status:—In Vietnam, this species is extremely rare. Although numerous particular fieldworks were conducted, only a few plants in one population were found in a vulnerable habitat with miserable occupancy. According to formal Red List IUCN (2022) criteria the species meets in Vietnam with the following conditions: the observed population reduction for 10 years or 3 generations ≥ 80% are not reversible (A2), based on direct observation (a) and observed decline of the area of occupancy, extent of occurrence and habitat quality (b); the area of occurrence <100 km ² (B1) and the area of occupancy <10 km ² (B2), with 1 known population (a) and continuing observed decline of extent of occurrence (bi); the area of occupancy (bii); area, quality of habitat (biii); the number of mature individuals (bv); the number of mature individuals <250, observed, estimated or projected continuing decline in 25% in 3 years or 1 generation (C1) and observed, estimated, projected or inferred continuing decline when the number of mature individuals in each subpopulation (C2(i)) ≤ 50 and % of mature individuals in one subpopulation = 90–100% (C2(ii)); the number of mature individuals <50 (D). Following these conditions, the conservation species status should be evaluated as nationally Critically Endangered (CR), CR A2a,c; B1+ 2a,b(i-iii,v); C1+2(i,ii); D.

Notes:—Species of this genus have a relatively broad distribution in the humid forests of tropical and subtropical Asia ( Robinson et al. 2016). However, individually, all of them are very rare plants, usually with limited distribution. Our discovery of Stigmatodactylus sikokianus in Vietnam, together with its recent report from northern Thailand ( Pedersen & Suksathan 2013), dramatically expands the area of the known species previously known only in Japan and eastern China (including Taiwan). Considering newly discovered locations, the species has the largest area among all other species in the genus.

Studied specimen:— VIETNAM, Dak Lak Province, Chu Yang Sin Mountains , lithophytic, tuberiferous herb on mossy rocks along a stream in evergreen broad-leaved forest, very rare, 7 August 2022, Nguyen Van Canh, s. n. (photo LE01123479 https://herbariumle.ru/?t=occ&id=140359) .

Figures

FIGURE 6. Stigmatodactylus sikokianus Maxim. ex Makino. A, B. Flowering plant in nature. C. Apical part of inflorescence (specimen 7 August 2022, Nguyen Van Canh, s. n.). All photos were made by V.C. Nguyen, with photo correction and design by L. Averyanov and T. Maisak.