Rhododendron chunii W.P.Fang subsp. vietnamense R.A.Baines & D.F.Chamb., 2021

Baines, R. A., Chamberlain, D. F., Nguyen, V. D. & Quang, B. H., 2021, TWO NEW TAXA OF RHODODENDRON (ERICACEAE) FROM VIETNAM, Edinburgh Journal of Botany 78 (363), pp. 1-8 : 4-7

Rhododendron chunii W.P.Fang subsp. vietnamense R.A.Baines & D.F.Chamb. , subsp. nov.

(subsect. Tsutsusi )

Rhododendron chunii subsp. chunii differs from the new subspecies in the young stems that bear appressed bristles that apparently lack the stipitate glands of subsp. vietnamense , and in the outer surface of the corolla tube that is glandular.

– Type: Cultivated at RBGE, Logan Botanic Garden (accession number 20150480), 23 iv 2019, Baines 73 (holotype HN, isotype E) . Figures 3 , 4 .

Small shrub, to 2 m; young shoots covered with erectopatent bristles, stipitate glands and flattened strigose red-brown hairs. Leaves monomorphic, coriaceous, persistent, elliptic to oblong-ovate, 1–2 × 0.5–0.9 cm, twice as long as broad, apex acuminate, base broadly cuneate, margin entire, upper surface strigose, lower surface paler, strigose, especially on midrib; petiole 2–3 mm, strigose. Inflorescence 2- to 3-flowered; pedicels 5–7 mm, densely brown-strigose. Calyx strigose; lobes 1–2 mm, oblanceolate. Corolla funnel-shaped, lilacpurple, upper lobes flecked, 9–10 mm; tube 6 × 3 mm, with 5 rows of glands on the outer surface, glandular within but glabrous outside. Stamens 5, subequal, filaments minutely hairy below. Ovary densely covered in fine brown hairs; style covered with fuscous setose hairs and glands in lower half. Capsule ovoid 5 × 4 mm, strigose.

Ecology. Temperate montane cloud forest, in wet thin soil with high humus content and high humidity. The surrounding vegetation is characterised by Enkianthus , Pieris and Rhododendron .

Phenology. The above description has been prepared from cultivated plants grown at Logan Botanic Garden from seeds collected in the wild in November 2014. The normal flowering time is mid to late April.

Conservation status. Data Deficient (DD) ( IUCN Standards and Petitions Subcommittee, 2019). At least four small populations are known on Phan Xi Păng Mountain, within the Hoang Lien National Park. We treat the conservation assessment of this subspecies as DD, awaiting more detailed fieldwork in northern Vietnam.

Cultivation. Rhododendron chunii subsp. vietnamense can tolerate full sun or partial shade and is hardy down to a minimum temperature of approximately –8°C. It requires damp, acidic soils that are freely draining but high in organic matter. When propagated from seed it can produce flowers in its third year and should reach a maximum height of 1 m.

Additional specimens examined. VIETNAM. Lao Cai Province: Sa Pa District, Phan Xi Păng Mountain, 2605 m, 22°19.208′N, 103°46.191′E [22°19′12.46′′N, 103°46′11.46′′E], 1 xi 2014, Baines et al. HNE 160 (source of seeds for RBGE accession 20150480) (E, HN, K). Sa Pa, Phan Xi Păng, Ton Station , 2605 m, 1 xi 2014, Hanoi, UBC, Logan, Longwood & Kew Expedition to Vietnam (2014) HNE 163 ( E [ E00787050 , E00787049 ]). Vietnam, screes on banks of a river above second camp and below Phan Xi Păng , 2300 m, 8 v 1992, K. Rushforth 2266 (E [E00039842]); ridge from Sin Chay village to first campsite, 2350 m, 3 v 1992, K. Rushforth 2242 (E [E00039840]); Camp 2 to the summit, narrow belt above first rock outcrop, 2550 m, 27 x 1994, K. Rushforth & D. Chamberlain, Rushforth 3011 (E [E00073374]).

Nguyen & Nguyen (2012) reported the existence of Rhododendron chunii in Vietnam, we assume based on the Rushforth specimens cited above. We are now aware of several collections of subsp. vietnamense that are consistent in the diagnostic morphological characters that distinguish this taxon from subsp. chunii . However, these are relatively trivial compared with the obvious similarities between the two subspecies. Furthermore, there are very few specimens available to us of subsp. chunii . We therefore cannot comment on the range of variation in the Chinese populations.

Subspecies chunii occurs at an altitude of 1100–1800 m in forested mountains in northern Guangdong Province, South China.

Figures

Figure 3. Rhododendron chunii subsp. vietnamense R.A.Baines & D.F.Chamb., subsp. nov. HNE 160, RBGE accession no. 20150480, flowering at Logan Botanic Garden. Photographs: R. A. Baines.

Figure 4. Rhododendron chunii subsp. vietnamense R.A.Baines & D.F.Chamb., subsp. nov. A, Floral parts highlighting tubular corolla, stigma and style (i), floral arrangement in terminal cluster (ii), and seed capsules (iii); B, flowering stem in cultivation; C, young stems with erectopatent bristles. Photographs: L. Wilson.