Dendrobium sect. Callista

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 : 20-22

Dendrobium sect. Callista

Dendrobium densiflorum Lindl. in Wallich (1830: 34), Holttum (1964: 282), Seidenfaden (1972a: 119, 1975a: 44, 1985: 23), Bose & Bhattacharjee (1980: 210), Banerji (1996: 59), Chen et al. (1999: 161, 2009: 376), Pearce & Cribb (2002: 403), Raskoti (2009: 94), Xu et al. (2010: 326), Rokaya et al. (2013: 524), Zhou et al. (2016: 47), Aung et al. (2020: 78), Ormerod et al. (2021: 99), Teoh (2021: 359), Jin et al. (2023: 337), Phonepaseuth et al. (2023: 32), non Gagnepain in Gagnepain & Guillaumin (1934: 214).

( Fig. 10B–D )

Type: — NEPAL. Sine loc., Wallich Wall. Cat. 2000 (holotype K, possibly K 000639690, isotype K fide Pearce & Cribb 2002).

Habitat and phenology in Vietnam: —Clustering epiphyte. Primary and old secondary evergreen, broad-leaved and mixed humid forests on granite and karstic limestone at elevations of 1100–2000 m a.s.l. Not common. Flowers in May–July.

Distribution: — Vietnam: border area between provinces Lai Chau and Lao Cai (sine loc.), border area between provinces Ha Giang (Bac Me District) and Tuyen Quang (Na Hang District). Nepal, NE India , Bhutan, Bangladesh, S China, Myanmar, Thailand, Laos.

Conservation status in Vietnam: —Two localities of Dendrobium densiflorum have been documented in the country. According to our observations, the habitat conditions in both discovered localities are influenced by selective logging. In addition, the populations are likely to decrease due to collecting for horticulture. Based on these conditions, we preliminarily estimate the national conservation status of D. densiflorum as Near Threatened (NT). Jin et al. (2023) assessed the status of this species as Vulnerable (VU) but have not provided any details or reasons for their decision.

Notes: —Herbarium specimens of Dendrobium densiflorum can be easily misidentified as D. thyrsiflorum Williams (1852: 61) that is very common in Vietnam. These two species are almost indistinguishable in dried material. As a result, the earlier reports of D. densiflorum in Vietnam (e.g. Gagnepain & Guillaumin 1934) remain doubtful (see also Seidenfaden 1985, 1992); most of them are likely to belong to D. thyrsiflorum . The main diagnostic feature of these species is the flower coloration: fresh flowers of D. densiflorum are characterized by yellow sepals and petals, clearly differing from those of D. thyrsiflorum with their pure white sepals and petals. At the same time, in Laos and northern Vietnam, there is an area of introgression between D. densiflorum and D. thyrsiflorum , and plants of intermediate morphology occur. Our discoveries reported here, documented by the herbarium materials and colour photos of living plants, represent the first verified records of D. densiflorum in the flora of Vietnam. According to these new data, D. densiflorum is a very rare mountainous species in Vietnam occurring only in the north and northwest parts of the country.

Studied specimens:— VIETNAM. Border area between Phieng Luong Municipality (Ha Giang Province, Bac Me District) and Sinh Long Municipality (Tuyen Quang Province, Na Hang District), primary broad-leaved humid evergreen and mixed forest on very steep slopes and along rocky ridge composed with solid crystalline highly eroded limestone at elevation of 1100–1170 m a.s.l. around point 22°38’24.3’’N 105°20’21.3’’E, epiphyte on old mossy tree, not common, 14 November 2014, L. Averyanov et al., fl. in cult. on 16 July 2019, L. Averyanov, CPC 7431a TM1130/1, sepals and petals light yellow, lip rich yellow, column light yellow, anther almost white with light yellow tint (LE LE01057743 https://en.herbariumle.ru/?t=occ&id=7890, photos LE LE01088565 https://en.herbariumle. ru/?t=occ&id=47760). VIETNAM. Border area between the provinces Lao Cai and Lai Chau, wild collected plant originated from Hoang Lien Son Range at elevation of 1500–2000 m a.s.l., cultivated in the orchid garden of Hoang Lien National Park Headquarter in Sa Pa Town, sepals and petals pale yellow, lip bright yellow, common, photos made on 25 May 2022, L. Averyanov, Tran Huy Thai, Khang Sinh Nguyen, T. Maisak, VR1800 (photos LE LE01123368 https://herbariumle.ru/?t=occ&id=137156).

Figures

FIGURE 10. A. Dendrobium lampongense. Photo by L. Averyanov from the specimen L. Averyanov, T. Maisak, AL2814. B–D. Dendrobium densiflorum. Photos by L. Averyanov from the specimen L. Averyanov et al., VR1800. E, F. Dendrobium nobile var. luteoalbum. Photos by L. Averyanov from living plant prior to the preparation of the type herbarium specimen L. Averyanov et al., LX- VN2107. G–I. Dendrobium polyanthum. Photos by L. Averyanov from the specimen L. Averyanov, T. Maisak, AL2816. Photo correction and design by L. Averyanov.