Dendrobium sect. Distichophyllum

Averyanov, Leonid V., Nguyen, Van Canh, Vuong, Truong Ba, Nuraliev, Maxim S., Nguyen, Khang Sinh, Maisak, Tatiana V., Yudova, Daria A., Saidov, Nikita T., Nguyen, Cuong Huu & Nong, Duy Van, 2024, New orchids in the flora of Vietnam VIII (Orchidaceae: Epidendroideae, tribes Malaxideae, Neottieae and Podochileae), Phytotaxa 658 (1), pp. 1-49 : 26

Dendrobium sect. Distichophyllum

Dendrobium deltatum Seidenfaden (1985: 185 , 1992: 239), Newman et al. (2007: 263), Schuiteman et al. (2008: 281), Phonepaseuth et al. (2023: 33).

( Fig. 12A–C )

Type: — THAILAND. Eastern part of Khao Yai National Park, 80 km at the Korat-Sattahip highway, wet evergreen forest, with Corypha and Tetrameles , epiphytic, white flowers, 300 m, 10 August 1968, K. Larsen, T. Santisuk, E. Warncke, 3256 (lectotype, designated here: AAU photo!, isolectotypes C C 10016195 photo!, K K 001085040 photo!).

Habitat and phenology in Vietnam: —Clustering epiphyte. Primary and secondary lowland evergreen broad-leaved forests on granite at about of 500 m a.s.l. Flowers in October–December (under cultivation).

Distribution in Vietnam: —Vietnam: provinces Quang Ngai (sine loc.), Dak Lak (sine loc.) and Khanh Hoa (sine loc.). Thailand, Laos.

Conservation status in Vietnam: —The species was once collected in the wild in Quang Ngai Province, and several times it was observed among the wild-collected plants offered for sale at local markets in Dak Lak and Khanh Hoa provinces. Taking into consideration the wide degradation of lowland forests across the area of species distribution and the high level of forest exploitation, we estimate the national conservation status of the species as Near Threatened (NT). The conservation status of this species outside Vietnam has never been evaluated.

Notes: —In the protologue of D. deltatum, Seidenfaden (1985) indicated the collection Larsen et al. 3256 as a type, and listed its duplicates deposited in three Herbaria (AAU, C and K) without designation of a place of holotype deposition. At that time, it has not precluded a valid publication of a new species (Art. 40.7 of ICN; Turland et al. 2018). We found a single duplicate of the type gathering in each of these Herbaria; these duplicates are to be treated as syntypes (Art. 9.6 of ICN). We selected the AAU specimen as the lectotype following Arts. 9.3 and 9.11 of ICN as it represents best the species.

Dendrobium deltatum is reported here as a new record for the flora of Vietnam. As outlined in the protologue, this species is very close to D. oligophyllum Gagnepain (1950: 743) widely distributed in Thailand, Laos, Cambodia and Vietnam ( Seidenfaden 1985, Averyanov 2013, Schuiteman et al. 2016, Averyanov et al. 2018a, Phonepaseuth et al. 2023), but differs from the latter in forward directed, triangular, acute side lobes of the lip. The new discoveries of D. deltatum in Vietnam result in very similar known distribution of these two species, supporting the idea that they are likely to represent marginal forms of a single species with a highly variable shape of the lip.

Studied specimens:— VIETNAM. Wild collected plant originated from Quang Ngai Province, evergreen broad-leaved forest, about 500 m a.s.l., epiphyte, common, flowered and collected under cultivation on 13 October 2018 in garden of Nguyen Van Canh in Buon Ma Thuot City, Nguyen Van Canh, AL 445 (LE LE01169574 https://herbariumle. ru/?t=occ&id=144142). VIETNAM. Wild collected plant originated from Dak Lak Province area and cultivated in garden of Nguyen Van Canh in Buon Ma Thuot City, photos made on 13 October 2018, L. Averyanov, T. Maisak, s.n. (photos LE LE01122967 https://herbariumle.ru/?t=occ&id=108767). VIETNAM. Wild collected plant obtained at Khanh Hoa street market and cultivated in Hanoi in garden of N. Phong, photos made on 17 December 2015, L. Averyanov, T. Maisak s.n. (photos LE LE01088780 https://herbariumle.ru/?t=occ&id=65288).

Figures

FIGURE 12. A–C. Dendrobium deltatum. Photos by L.Averyanov from the specimen L. Averyanov, T. Maisak, AL2825. D–F. Oberonia maxima. Photos by Truong Ba Vuong from the specimen Truong Ba Vuong, Ngo Quang Dang, BV889. Photo correction and design by L. Averyanov.