Didymoplexiella laosensis S.W.Gale & Kumar

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 : 21-24

1. Didymoplexiella laosensis S.W.Gale & Kumar in Kumar et al. (2020: 2, Fig. 1 , 2 , 3A,B ) ( Fig. 2 , 3 )

Kumar et al. (2016: 2, Fig. 1b , as Didymoplexiella sp. 1 ).

TYPE: — LAOS. Vientiane Province: Vang Vieng District, Phone Ngueng Area , 280 m elevation, 26 April 2012, Gale, Kumar, Santainsy, Phunthavong, HNL-KFBG 0007 (holotype HNL , isotype KFBG ).

Ecology and phenology: —The species occurs between rocky crevices under broad-leaved lowland forest on limestone karst, under dry semi-deciduous forests on slopes of sandstone ridges, in humid evergreen submontane forests, usually among leaf litter in shady places, at elevations of 200– 850 m. Flowers from April to September (October).

Distribution: — Laos: Vientiane Province (Vang Vieng District), Khammoune Province (Nakai-Nam Theun National Park, Hin Nam No National Park). Vietnam: Quang Nam Province (Cu Lao Cham Island), Gia Lai Province (Kon Ka Kinh National Park).

Conservation status: —In the protologue of D. laosensis , its conservation status was reasonably assessed as Endangered (EN B1+B2ab(iii)) based on the study of three scattered populations found in Vang Vieng District (Kumar et al. 2020). Additional locations of this species reported here considerably expand its known occurrence area and lead to the following amendment according to the criteria proposed by the IUCN Red List (2023): less than 10 distribution sites are recorded, the AOO does not exceed 500 km 2, and therefore the global conservation status is estimated as Endangered (EN B2ab(iii); B2 for AOO<500 km 2, a for severely fragmented populations, b for continuously declined quality of habitat).

Notes:

1. Didymoplexiella laosensis shows considerable morphological similarity with D. trichechus , and appears to differ from the latter species by oblong rectangular (vs obliquely quadrate to angular-round) side lobes of the labellum that project (vs do not project) beyond the median lobe (along the median axis of flower). Some of the specimens assigned here to D. laosensis (e.g. Averyanov et al. AL 891: Fig. 3G , Tran Minh Duc et al. LTA 984) have side lobes of the labellum somewhat shorter than those described and illustrated in the protologue, hardly projecting beyond the median lobe. Such specimens approach D. trichechus in their morphology and make the delimitation between the two species imperfect.

Additionally, an uncertainty exists regarding the range of variation of the labellum shape in D. ornata , which complicates consideration of the distinctness of D. laosensis from this species (see below).

2. Kumar et al. (2020) stated that in D. laosensis the longitudinal callus of the labellum terminates in more than 0.5 mm from the apex of the median lobe, and used this feature for differentiation of the species from D. ornata , D. siamensis and D. trichechus . However, this statement contradicts their drawing Fig. 2E , and furthermore, additional specimens of D. laosensis studied here demonstrate this character to be equal to that of the other Indochinese species of Didymoplexiella .

3. Didymoplexiella laosensis is reported here for the flora of Vietnam for the first time.

Three of the specimens cited here under D. laosensis were earlier assigned to other species of the genus: Averyanov et al. AL 891 from Laos was listed as D. ornata ( Averyanov et al. 2019b) , Averyanov et al. AL 1086 from Laos was listed as D. ornata ( Averyanov et al. 2019b) or D. trichechus ( Averyanov et al. 2019a) , and Nuraliev 1781 from Vietnam was listed as D. ornata ( Nuraliev et al. 2019) . After the description of D. laosensis , it became clear that these three specimens fit best the concept of this species in their long rectangular side lobes of the labellum usually projecting beyond the median lobe.

4. For D. trichechus , the indication by Averyanov et al. (2019a) based on the specimen Averyanov et al. AL 1086 was the only published record from the countries of Eastern Indochina, and therefore we here reconsider the species as unknown from their territories.

Additional specimens examined:— LAOS. Khammoune Province: Boualapha District, Langkhang Village, Nakai-Nam Theun Protected Area, steep southern slopes of sandstone ridge allied to the road from the north, around point 17°34’02.2’’N 105°42’42.6’’E, 200–535 m a.s.l., primary lowland semi-deciduous and evergreen dry forest on very steep rocky slopes, terrestrial achlorophyllous aphyllous herb to 20 cm tall on steep rocky slope, rare, 15 May 2018, L.V. Averyanov, Khang Sinh Nguyen, T.V, Maisak AL 1086 ( LE: LE 01048691 https://en.herbariumle.ru/?t=occ&id=478);

Boualapha district, Ban Dou Village, Hin Nam No Nature Protected Area, around Khuay Cave, 17°30’35.1’’N 105°51’28.7’’E, primary dry evergreen and semi-deciduous broad-leaved forest on very steep rocky slope near karstic hill top composed with solid, marble-like highly eroded limestone at 250–390 m a.s.l., achlorophyllous terrestrial herb on shady rocky slope, locally common, 10 May 2018, L.V. Averyanov, Khang Sinh Nguyen, T.V. Maisak, Littideth Xaiyavongsa, Siphanom Keovankham AL 891 ( LE: LE 01048669 https://en.herbariumle.ru/?t=occ&id=53, LE 01048781 https://en.herbariumle.ru/?t=occ&id=3050).

VIETNAM. Quang Nam Province: Hoi An City, Tan Hiep Municipality, Cu Lao Cham Island, 29 September 2020, Tran Minh Duc, Dinh Dien, Le Tuan Anh LTA 984 (photos LE: LE 01088173 https://en.herbariumle.ru/?t=occ&id=43691);

Hoi An City, Tan Hiep Municipality, Cu Lao Cham Island, primarily dry semi-evergreen broad-leaved forests on sandstone mountains, around point 15.95000°N 108.52542°E, terrestrial holomycotrophic herb up to 20 cm, flower pinkish white, elevation of 200–450 m a.s.l., occasional, 23 June 2022, Nguyen Sinh Khang, Nguyen Huu Cuong, Dang Van Ha, Cao Xuan Hai 001 (photos LE: LE 01123549 https://en.herbariumle.ru/?t=occ&id=141856); same location, 24 June 2022, Nguyen Huu Cuong, Dang Van Ha, Nguyen Sinh Khang, Cao Xuan Hai CHKH 202206243073 (photos LE: LE 01123550 https://en.herbariumle.ru/?t=occ&id=141857);

Gia Lai Province: K’Bang District, K’rong Municipality, Kon Ka Kinh National Park, 25 km NW of K’Bang Town, forest, 14°18’25’’N 108°26’21’’E, elevation 820 m, 14 May 2017, M. S. Nuraliev 1781 ( LE: LE 01067821 https://en.herbariumle.ru/?t=occ&id=17410, photos LE 01089023 https://en.herbariumle.ru/?t=occ&id=65552).

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.