Didymoplexiella siamensis (Rolfe ex Downie) Seidenfaden (1972: 99)

Nuraliev, Maxim S., Averyanov, Leonid V., Nguyen, Khang Sinh, Nguyen, Cuong Huu, Le, Tuan Anh, Maisak, Tatiana V., Lyskov, Dmitry F., Kuznetsov, Andrey N. & Kuznetsova, Svetlana P., 2023, The mycoheterotrophic genus Didymoplexiella (Orchidaceae) in Cambodia, Laos and Vietnam, Phytotaxa 620 (1), pp. 18-32 : 26-30

3. Didymoplexiella siamensis (Rolfe ex Downie) Seidenfaden (1972: 99) ( Fig. 5 , 6 )

Maekawa (1977: Fig. 1 , 2 ), Seidenfaden (1978: 176: Fig. 109), Su (2000: 851, Pl. 360), Averyanov & Averyanova (2002: 74, 2003: 31), Averyanov (2006: 62, 2013: 159, Fig. 80e–g, 81d), Chen et al. (2009: 206, Fig. 275), Hu et al. (2014: 178, Fig. 1A–D , 2 ), Suddee (2014: 481, Fig. 267, Pl. 40-1), Shen et al. (2015: 286, Pl. 1), Inoue (2016: 260), Lin et al. (2016: 94), Zhou et al. (2016: 52), Gale et al. (2018: 127), Suetsugu et al. (2019: 190, Fig. 1 ), Kumar & Gale (2020: 52), Schuiteman et al. (2022: 132, Fig. 16, 17).

≡ Leucolena siamensis Rolfe ex Downie (1925: 416) . Seidenfaden & Smitinand (1959: 73, Fig. 54).

≡ Didymoplexis siamensis (Rolfe ex Downie) Suetsugu & T.C.Hsu (2019: 177) .

LECTOTYPE (designated by Seidenfaden 1978: 176):— THAILAND. Chiang Mai Province: Doi Suthep , on humus in evergreen jungle, 2300 ft [700 m], 8 May 1910, A.F.G. Kerr 245 ( K: K000942689 https://www.gbif.org/occurrence/912692189 photo!).

= Didymoplexiella denticulata Averyanov (2010: 92 , Fig. 3 , 4 ). Averyanov (2011: 57, Fig. 26, 27h,i, 35).

TYPE: — VIETNAM. Quang Binh Province: Le Thuy District, Kim Thuy Municipality, around Lang Ho village at 16°59’31’’N 106°38’31’’E, old secondary broad-leaved closed forest on steep shale slopes of Khe Nuoc Trong River at elevation 150–200 m a.s.l., terrestrial achlorophyllous herb on steep shady slope, flowers light violet-brown, lip light violet with white apex, column white, not common, 9 April 2008, L. Averyanov , P. K. Loc , N. T. Vinh , N. S. Khang HAL 11443 (holotype HN!, isotypes LE: LE01067829 ! https://en.herbariumle.ru/?t=occ&id=17417, MO: 100182465!, photos LE01089015 https://en.herbariumle.ru/?t=occ&id=65544, LE01089016 https://en.herbariumle.ru/?t=occ&id=65545) .

= Didymoplexis siamensis var. amamiana Suetsugu in Suetsugu & Hsu (2019: 177) .

TYPE: — JAPAN. Ryukyu Islands: Kagoshima Prefecture, Amami-Oshima Island, Amami City , Naze , 5 May 2018, Morita N15-04 (holotype TNS, a flower in the spirit collection).

Ecology and phenology: —The species grows in tropical to warm temperate regions, among leaf litter in shady primary to secondary humid to dry evergreen (or semi-evergreen and rarely deciduous) broad-leaved and mixed forests on limestone, shale and sandstone, at elevations of 100–1000 m. Flowers from March to July.

Distribution in the region of study: — Laos: Sekong Province (La Mam district). Cambodia: Koh Kong Province (Ta Tey Leu). Vietnam: Tuyen Quang Province (Na Hang District), Nghe An Province (Pu Mat National Park), Quang Binh Province (Phong Nha-Ke Bang National Park and districts Quang Ninh and Le Thuy), Quang Tri Province (Huong Hoa District and Da Krong District), Lam Dong Province (Bao Lam District).

Distribution worldwide: —S Japan: Kagoshima Prefecture (Tanegashima, Yakushima and Amami Oshima islands). S China: Guangxi (Shiwandashan National Nature Reserve), Hong Kong. Taiwan: Taipei County (Chachiao), Pingtung County (Hengchun Peninsula). Thailand: Chiang Mai Province (Doi Suthep), Lampang Province (Doi Luang National Park), Phitsanulok province (Thung Salaeng Luang), Phetchabun Province (Nam Nao).

Hainan is excluded from the known distribution of the species following the clarification by Hu et al. (2014).

Conservation status: —Locations of the species are confirmed in S Japan, S China, Taiwan, Thailand, SE Laos, SW Cambodia and Vietnam, forming a polygon with an extent of occurrence (EOO) greater than 1,000,000 km 2. The species therefore does not fit any criteria of threatened conservation categories proposed by the IUCN Red List (2023). Meanwhile, D. siamensis , as well as all its congeners, is strongly habitat-conservation-dependent and surely cannot survive on degraded soils in secondary plant communities. Taking into consideration the pronounced ongoing deforestation in the area inhabited by D. siamensis , we tentatively assess its conservation status as Near Threatened (NT).

Notes:

1. Hu et al. (2014) analysed the type material of D. siamensis and stated that they have designated a lectotype for this species. However, the lectotypification was performed prior to their study by Seidenfaden (1978), as shown below. Seidenfaden’s choice (which is identical with the one made by Hu et al.) has a priority according to Art. 9.19 of ICN ( Turland et al. 2018).

Downie (1925) cited two gatherings in the protologue of Leucolena siamensis, Kerr 245 and Kerr 305, both made in Doi Suthep. These gatherings should be treated as syntypes following Art. 9.6 of ICN ( Turland et al. 2018). Downie did not indicate the place of their deposition. Seidenfaden (1978) indicated the specimen Kerr 245 at K as “type”, which at that time met the conditions for effective lectotypification (Art. 7.11 of ICN, Turland et al. 2018).

Kumar & Gale (2020) cited the barcode K000942688 for the lectotype of D. siamensis (Kerr 245), which is a mistake, because this barcode belongs to another gathering, Kerr 305 (a remaining syntype of this species), mounted on the same sheet with K000942689.

2. Didymoplexis siamensis var. amamiana was described by Suetsugu & Hsu (2019) within their broad concept of the genus Didymoplexis , which implied merging of Didymoplexiella with Didymoplexis . This variety is treated as a synonym of Didymoplexiella siamensis in the POWO online database ( Govaerts et al. 2023). We find this decision reasonable, because the variety was described as differing from Didymoplexiella siamensis s.s. solely by the very short stelidia. Indeed, the stelidia of Didymoplexis siamensis var. amamiana are much shorter than the anther, as seen in Fig. 1 from Suetsugu & Hsu (2019), whereas in Didymoplexiella siamensis s.s. (and in all the other species of Didymoplexiella ) the stelidia are linear and at least twice longer than the anther (see references above). Suetsugu & Hsu (2019) described the variety on the basis of a single population, located in several hundred meters from a population characterised by long stelidia.

Additional specimens examined:— THAILAND. Chiang Mai Province: Doi Suthep, deer valley, on humus in evergreen jungle, 3000 ft [915 m], 19 May 1912, A. F. G. Kerr 305 (remaining syntype, K: K 000942688 https://www. gbif.org/occurrence/912692245).

LAOS. Sekong Province: photo provided by Gale et al. (2018).

CAMBODIA. Koh Kong Province: east of Ta Tey Leu, damp forest on a slope above a stream, 490 m elevation, 22 April 2018, Schuiteman et al. 18-44 ( K, photos seen).

VIETNAM. Tuyen Quang Province: Na Hang District, Xuan Tam Municipality, near Ban Cai village (22°29’18’’N 105°19’47’’E), primary broad-leaved evergreen dry forest on very steep slopes of highly eroded remnant limestone ridge at elev. 450–500 m a.s.l., dry steep slope with bamboo, terrestrial tuberiferous saprophyte, flowers with strong, very pleasant fragrance, tepals light purple-violet, column white, rare, 22 March 2001, P. K. Loc, N.X. Tam, L. Averyanov HAL 218 (paratypes of D. denticulata ; HN, LE: LE 01067841 https://en.herbariumle.ru/?t=occ&id=17428, photos LE 01089014 https://en.herbariumle.ru/?t=occ&id=65543);

Nghe An Province: Tuong Duong District, Tam Quang Municipality, Tung Huong village, [Pu Mat National Park,] along Khe Mat stream around point 19°03’07’’N 104°36’57’’E at elevation about 400–500 m a.s.l., lowland closed secondary old evergreen forest on steep slopes along rocky stream valley composed with stratified solid shale and sandstone, along ridge, terrestrial achlorophyllous herb, flowers bluish, very fragrant, very rare, 17 March 2007, L. Averyanov, P. K. Loc, N.V. Trai, N. T. Vinh, N.D. Phuong, A. Averyanova HLF 6672 (paratypes of D. denticulata ; HN, LE: LE 01067845 https://en.herbariumle.ru/?t=occ&id=17433, MO: 100178408);

Quang Binh Province: Bo Trach District, Tan Trach Commune, Phong Nha-Ke Bang National Park, forest, 17°27’30’’N 106°12’56’’E, elevation 550 m, 26 March 2022, M. S. Nuraliev, D. F. Lyskov, L.X. Dac, L.M. Ha, D.Q. Thang NUR 3540 ( LE: LE 01168129 https://en.herbariumle.ru/?t=occ&id=134412, photos LE 01123111 https:// en.herbariumle.ru/?t=occ&id=134290);

Bo Trach District, Tan Trach Commune, Phong Nha-Ke Bang National Park, forest, not far from dry river bed, 17°26’44’’N 106°13’05’’E, elevation 320 m, 27 March 2022, M. S. Nuraliev, D. F. Lyskov, L.X. Dac, L.M. Ha, D.Q. Thang NUR 3557 ( LE: LE 01168130 https://en.herbariumle.ru/?t=occ&id=134413, photos LE 01123115 https:// en.herbariumle.ru/?t=occ&id=134294);

Quang Ninh District,Truong Son Municipality, around Chan Trong village at 17°10’49’’N 106°29’22’’E, secondary dry broad-leaved forest on tops and steep slopes of highly eroded karst limestone mountain composed with gray solid marble limestone allied to Long Dai River, at elevation 300–400 m a.s.l., terrestrial achlorophyllous dull graybrownish saprophyte, flowers light violet, not rare, 13 April 2008, L. Averyanov, P. K. Loc, N. T. Vinh, N. S. Khang HAL 11521 (paratypes of D. denticulata ; HN, LE: LE 01067833 https://en.herbariumle.ru/?t=occ&id=17421, LE 01067853 https://en.herbariumle.ru/?t=occ&id=17441, MO: 100182792, photos LE 01089017 https://en.herbariumle.ru/?t=occ&id=65546);

Quang Tri Province: Huong Hoa District, Huong Phung Municipality, Sa Mui pass, around point 16°47’42’’N 106°35’50’’E at elevation about 1000 m a.s.l., secondary broad-leaved evergreen submontane forest on shale mountains, rocky shady stream slope with bamboo, terrestrial achlorophyllous olive-brownish to nearly black saprophyte, flowers white, lip light blue-violet, not common, 28 March 2006, L. Averyanov, P. K. Loc, P.V. The HLF 6263 (paratypes of D. denticulata ; HN, LE: LE 01074683 https://en.herbariumle.ru/?t=occ&id=17594, photos LE 01089021 https:// en.herbariumle.ru/?t=occ&id=65550, LE 01089022 https://en.herbariumle.ru/?t=occ&id=65551);

Da Krong District, Huc Nghi Municipality, in vicinities of La To village around point 16°29’16’’N 107°00’32’’E at elevation about 414 m a.s.l., secondary broad-leaved evergreen lowland forest on montane hills composed with shale, very steep shady wet slope, achlorophyllous terrestrial saprophyte, flower white, very rare, 26 March 2006, L.Averyanov, P. K. Loc, P.V. The, N. S. Khang, N.V. Huy, D. C. Tri, L.M. Tuan, T. T. Tu, P. K. Vuong, P.V. Bao, P.X. Dieu, H. T. Phuong HLF 6216 (paratypes of D. denticulata ; HN, LE: LE 01067837 https://en.herbariumle.ru/?t=occ&id=117679, photos LE 01089019 https://en.herbariumle.ru/?t=occ&id=65548, LE 01089020 https://en.herbariumle.ru/?t=occ&id=65549);

Lam Dong Province: Bao Lam District, Loc Bao Municipality, 7 km NW of Loc Bao town, forest, near rocky river bank, 11°50’19’’N 107°38’37’’E, elevation 500 m, 21 April 2012, M. S. Nuraliev 586 ( LE: LE 01067825 https:// en.herbariumle.ru/?t=occ&id=17413, photos LE 01089025 https://en.herbariumle.ru/?t=occ&id=65554).

Figures

FIGURE 1. Distribution map of the species of Didymoplexiella in Cambodia, Laos and Vietnam (the map is not aimed to show countries in their entire borders).

FIGURE 2. Didymoplexiella laosensis. A. Inflorescence.B–D. Flowers in different views.E, F. Labellum and column (side and semi-side view). G. Flower (back view). H. Column (front view). I. Rhizome. Nuraliev 1781. Photos by M.S. Nuraliev.

FIGURE 3. Didymoplexiella laosensis. A. Habit. B–H. Flowers in different views. I. Column (semi-adaxial view).A–C: Averyanov et al. AL 1086; D, E. Nguyen S.K. et al. 001; F, G: Averyanov et al. AL 891; H, I: Nguyen H.C. et al. CHKH 202206243073. Photos A–C, F, G by L.V. Averyanov; D, E. by S.K. Nguyen; H, I by H.C. Nguyen.

FIGURE 4. Didymoplexiella ornata, dried material. A. Flower with labellum removed. B. Sepals and petals. C, D. Labella (adaxial view). E. Column (adaxial view). F. Flower. Hiep NTH 6271. Photos by L.V. Averyanov from LE01067822.

FIGURE 5. Didymoplexiella siamensis. A. Inflorescence. B–E. Flowers in different views. F. Labellum and column (semi-side view). G. Labellum (side view). H. Labellum and column (top view). I. Column (adaxial view). J. Rhizome.A–I: Nuraliev et al. NUR 3557; J: Nuraliev et al. NUR 3540. Photos by M.S. Nuraliev.

FIGURE 6. Didymoplexiella siamensis (paratypes of D. denticulata). A. Habit. B–E. Flowers in different views. F. Inflorescence. G, H. Flowers (semi-side views). A–E: Averyanov et al. HLF 6263; F: Averyanov et al. HLF 6216; G, H: Averyanov et al. HAL 11521. Photos by L.V. Averyanov.